Category: Beach Stones

The Fossilised Worm Cast Stones of Gemstone Beach and Riverton – Part One: Initial Identification

Large fossil worm cast stone, near McCracken’s Rest, Orepuki. It was too large to tumble polish so I did not take it home with me.
Other side of large fossil worm cast stone, near McCracken’s Rest, Orepuki
Fossil worm cast stone on Gemstone Beach
Fossil worm cast stones found on Gemstone Beach, May 2019

The tourist information on Gemstone Beach near Orepuki, 29 kilometres west of Riverton, sometimes mentions that fossil worm cast stones can be found there. For example: “A few hours beachcombing could easily yield gems such as hydrogrossular, jasper, fossil worm casts and the elusive sapphire” (Heritage Trail website). The Heritage Trail sign that used to stand at Gemstone Beach also mentions fossil worm casts.

Gemstone Beach Heritage Trail
Source: https://talltales.me/2013/02/24/the-south-of-the-south/photo-2-01-13-10-30-21-am

Over the past couple of years, I have believed that the sort of stones being referred to here would have within them, or on them, the fossilised remains left by worms at the bottom of the sea, these remains being the castings excreted by them as they fed. This series of Posts reports on the research I have done to check out this belief.

The photos below show what I have come to think of as fossil worm cast stones. They have all been collected by myself mostly from Gemstone Beach but some also from Riverton beaches:

Polished fossil worm cast stones from Gemstone Beach.
Fossil worm cast stone 1
Fossil worm cast stone 2
Fossil worm cast stone 3
Fossil worm cast stone 4
Fossil worm cast stone 5
Fossil worm cast stone 6
Fossil worm cast stone 7
Fossil worm cast stone 8
Fossil worm cast stone 9

In a small entry on types of fossils written by Hamish Campbell in 2006 in Te Ara The Encyclopedia of New Zealand, the example of a fossilised worm burrow is very similar to the stone in the photo centre right above. Campbell writes: “The worm-like impression is called a trace fossil, as it shows traces left by a worm burrowing through mud.” 

Te Ara fossil types
Top left is a rock with a fossilised worm burrow. Source: https://teara.govt.nz/en/photograph/9020/three-types-of-fossil

Note that Campbell mentions “burrows”, not “casts”. Maybe the distinction is important – we will return to this in a later Post.

Furthermore, the Riverton Museum Te Hikoi includes two “worm trace fossil” stones in one of it rock drawers (see photo below). They look similar to some of the ones I have collected on Gemstone Beach and Riverton.

Te Hikoi wc
Riverton Museum Te Hikoi display. Photo taken with permission.

Jocelyn Thornton’s (1985) book, “Gemstones”, has a page on “Orepuki Beach Pebbles” (page 36). She refers to a group of stones (number “5” in her diagram) as follows: “Those at the top of this group clearly show layers of mud, worm trails and wave ripples…” (see photos below). She uses the term “trail” and not “cast”. None of these stones really look like the fossil worm cast stones I have found.

Page 36 of Jocelyn Thornton’s (1985) “Gemstones”. Source: https://www.onnaturesedge.co.nz/downloads/nzgemstones.pdf
Detail of page 36 of Jocelyn Thornton’s (1985) “Gemstones”. Source: https://www.onnaturesedge.co.nz/downloads/nzgemstones.pdf

The next Post in this series will look more closely at what a “trace” fossil is. Part Three (July 2019) looks in detail at the trace shapes found in the stones. After writing Part Three, I conducted research into the origin and age of these trace fossils. Part Four, written in September 2019, reports on information from someone in the Department of Geology at the University of Otago who knows something about trace fossils. Part Five was not published until July 2024 and describes my research on a number of topics, mainly the role of the Brook Street Terrane in the formation of the trace fossils along the south coast.   

16 Gems – Stones for Poetry

In People and Places, Poems and Stones: Kay McKenzie Cooke and Orepuki, I introduced the poet, Kay McKenzie Cooke, and discussed her links to her childhood home, Orepuki. I noted how stones from Gemstone Beach have figured in her life and poems. I thoroughly enjoyed reading her latest book of poems, Born To A Red-Headed Woman, so much so that I offered Kay some polished Gemstone Beach stones to acknowledge my enjoyment. And because I knew she would really appreciate and value them. 

16 polished stones from Gemstone Beach
Kay reading poetry at the Orepuki Beach Cafe, 2015. Source: http://whistlestoptours.blogspot.com/2015/06/early-march-2015-saw-j-and-k-rolling.html

I wanted to include a fossil worm cast stone and a hydrogrossular garnet and a banded rhyolite. I picked out a few more recently polished ones for consideration as well. In preparation for sending the stones in the mail to Kay, I photographed them and started to number them so I could include a description of them, outlining what kind of stone each one is (if I know).  I then thought about a more creative way of identifying each stone – why not link them to the lines of the poems in her book? This process resulted in 16 stones being chosen and named. As I said to Kay in an email at the time, “The stones I had polished and the poems you had written proved a very fertile ground for linkages. I really enjoyed working through the ideas, it was not at all a hard thing to do. It was interesting how much colours are used in your poems. And the colours often carry the emotional dimensions which are deep.”

The following is what I sent to Kay – lines from her poems in Born To A Red-Headed Woman are in green, with page numbers. Her poems are autobiographical and chronological, starting with her birth, going through her childhood, high school, and on into adulthood, motherhood, and being a grandmother. The sequence of stones follow the sequence of this life journey. Each poem is named after a song or lyric associated with that time or relevant to its theme.

Sometimes, below, the meaning of just a couple of lines from a poem may not be clear – you’ll have to buy the book! 

**********

TumbleStone Reflections on “Born to a Red-Headed Woman: Poems by Kay McKenzie Cooke” (Otago University Press, 2014)

Sixteen Polished Stones from Gemstone Beach

Stone 1, “Moonlight”: Whiteish-yellowish-orangeish quartz stone the size of a small walnut, brought down the Waiau River and cast upon the beach on the coast

don’t let the moon break your heart

I was born in winter
to a red-headed woman
who shivered on a hard bed
under one thin blanket
in a hospital by the Waiau River
making heavy work

of its final punch through
to the coast,
the thrum of its waters
underscoring our breathing,
the beating of my heart
the size of a walnut.
(page 12)

Stone 2, “Misty”: Translucent hydrogrossular garnet, like the mist made by fingertips

The teacher draws close,
her own fingers cool,

narrow, streamlined
dragonflies that touch down
briefly where my fingertips
have begun to make mist,
What lovely moons you have, she says.
(page 15)

Stone 3, “Near Light”: Dark and light banded mudstone, the night and the light

On the night of our send-off
oblivious to what I was leaving behind:
the near light of Te Waewae Bay
(page 18)

Stone 4, “White Dresses”: Dark red stone (jasper?) with a pattern of white speckles (quartz?)

At the Riversdale Girl Guides
we practised
Scottish Country Dancing…

…we rehearsed
reels in white dresses
with tartan sashes…
(page 22)

Stone 5, “Sago Pudding”: White quartz

…Dad singing, Pass the biscuits, Miranda
as all nine of us ate mashed spuds
and Mum’s mince stew with carrots,
followed by sago pudding
(page 23)

Stone 6, “Green Sea”: Green mudstone with dark green bands

…I dip below the ridge
to follow the crack of an old creek-bed
and all around nothing but green, green.
Green. A sea of green.
(page 24)

Stone 7, “Loneliness”: Grey marble-like stone, with dark staining on one side

Released the year and month my father died,
‘Wichita Lineman’ can still bring me the valley
where we lived,
still bring me grief, the sound

of wind through wire, the loneliness
of country verges
(page 32)

Stone 8, “Wild Green”: Green quartzite stone

We’d cut through the Gardens,
where the caged kea was kept…
its keening call sounding
as if it expressed the same ache
we felt
of sudden transplantation
from wild green.
(pages 36-37)

Stone 9, “Flat”: A flat stone, igneous porphyry with light-coloured crystals

Inside a stone flat in Dunedin…
is where I gave up butter
and coal-range heat…
(page 40)

Stone 10, “Sorrow’s Green Depths”: Blue-green stone with small pink spots

The sound of a snip.
And it is done.

and sometimes there will be sorrow

Sunday in Hedgehope
in a wooden house
with a front verandah,
in the depths
of Southland’s green.
(page 43)

Stone 11, “Ancestors”: Green argillaceous mudstone containing fossil worm casts

We saw Loch Ness and travelled in sunshine
up the Great Glen. That day we were riding
the land our ancestors walked.
(page 49)

Stone 12, “Worlds”: Small grainy white and black schist stone

We wore out what was left
before middle-age, being there
for both the fragile and the strong.
Every night remnants
from the sandpit, tiny grains of sand,
whole worlds,
carried home between our toes.
(page 51)

Stone 13, “Budgie”: Whitish greenish stone with clear patches, hints of yellow and black specks

Sometimes all it is
is being on holiday stuck in a car together…
Sometimes, it’s the wind slamming a door
shut. Sometimes it’s the day the budgie dies
or the way the passage smells when it rains.
(page 54)
 
Stone 14, “Lara’s Theme”: Small delicate quartzite stone, with clear silica bands

Before giving her up for adoption,
I’d called my baby daughter Lara…
…We love telling people
the surprise ending.
(page 56)

Stone 15, “Black-Faced”: Predominantly black crescent-shaped stone, with faint light patterning

Tomorrow
our son will take us into country so deep
we can only stand on the brink

looking up at that black-faced bluff
where the helicopter he was in crashed
and thank God that he survived.
(page 61)

Stone 16, “Space”: Banded rhyolite

it feels new
(for my grandchildren)

I look hard into your eyes,
see earth around a seed,
sea around an island,
space around a star.
(page 70)

**********

Kay’s response can be found in a Post called “Gems” in her own blog “Cuttings”. I have also used Kay’s poetry in the Post Green and Black: Green Stones and Mary Black’s “The Moon and Saint Christopher”.

People and Places, Poems and Stones: Kay McKenzie Cooke and Orepuki

Kay reading poetry at the Orepuki Beach Cafe, 2015. Source: http://whistlestoptours.blogspot.com/2015/06/early-march-2015-saw-j-and-k-rolling.html
Kay’s photo of Taunoa Stream, Gemstone Beach. Source: https://kaymckenziecooke.com/2019/05/09/charmed-place

A few weeks ago, on an aeroplane, I read Kay McKenzie Cooke’s book of autobiographical poems, Born To A Red-Headed Woman (2014). I was flying south, on my way via Invercargill, Gore and Riverton to Orepuki, the place where she grew up. I read all the poems at one sitting, and was transported in space and time beyond that morning’s plane journey to my own past and to the places that we unknowingly shared many years ago – the beaches of the southern coast, parts of rural Southland, the town of Gore and its high school, the big city of Dunedin. Kay lived in Orepuki for only ten years, but I understand the deep feelings she has for that place and how it remains strongly influential in her life and poetry. I grew up on “The Mains”, a farm just outside of Waikaka, leaving there when I went to university. I still think of it as “home”, and many parts of that farm are clear images in my head and still have strong emotional meanings for me. I have come to know Orepuki as the town near to Gemstone Beach, a place where I collect magnificent little stones, but seeing it through Kay’s eyes adds significant depth and meaning. 

I used to write a column for “The Smallfarmer” magazine, about 17 or 18 years ago. One of my articles was titled “The Passions and Emotions of Smallfarming: Place, Experience and Meaning”. I started it with this comment: “Geographers have argued for some time that a place is not simply the sum of its physical and biological components. Rather, places are peopled, and have significance to people in a wide variety of ways. Places are centres of meaning constructed by experience… They have emotional value and meaning to us.” I argued that different parts of a smallfarm (or of any place, in fact) can have different emotional meanings at different times to people, and these intensify or even change as the years pass. Lived-in places have “emotional micro-regions”, small areas charged with emotions based on the experiences we have there. 

In that article, I explored different types of “emotional micro-regions”. There are areas associated with delight, with stimulation, or with joy, which are keenly felt positive emotions. Gemstone Beach, for example, is full of those experiences for me, where the discovery of a colourful or rare stone brings a surge of emotion. Such emotions have come to be associated with the preparations for any visit to that beach. Then there are regions of comfort, security, and relaxation, positive but more passive emotions. Sitting on the high bank of stones half-way through a stone collection expedition, eating a refreshing mandarin or bar of chocolate, or finally reaching the carpark and warmth of the car after nearly three hours on a cold and windy beach – these constitute such micro-regions. 

Gemstone Beach, a region of delight
The delight of a gorgeous Gemstone Beach stone, found by Sam, my great-nephew
The surprise and delight of finding a sought-after stone
A refreshing stop on the stone bank, safe from the waves
The view of Gemstone Beach while taking a refreshing break. This part of the beach becomes associated with this emotional experience.

Negative passive place emotions include boredom, dissatisfaction, and tedium. Gemstone Beach does not hold such areas for me. But I can imagine that someone accompanying me, who has no interest in stones and really wants to be somewhere else, would come to have that kind of emotional experience of that place. Finally, there are the places that may be associated with stress, anxiety, tension, and frustration, even sadness, fear and anger, the more keenly felt negative emotions. Crossing the swift-flowing Taunoa Stream, or walking eyes-down along the edge of the waves, have sometimes resulted in the discomfort of cold water in the gumboots. And the pounding of powerful waves on a stormy day, when I have a high bank of stones restricting my ability to elude a wave stronger than the previous one, can be an anxious experience. 

Drying out my gumboots on Gemstone Beach on a cold June day, 2019.
The discomfort of the wave washing in over your gumboots.
The anxiety of being so close to powerful waves breaking on Gemstone Beach.
The anxiety of being so close to a crumbling stone bank as the Waimeamea River seeps out through the stones

Emotional micro-regions are not fixed – they may last for only a short time, though the memory and subsequent association remains. And they often overlap – the same place can have both positive and negative associations related to a number of different events or visits that have occurred over the years. Gemstone Beach is an amalgam of emotional micro-regions built up from the experiences I have had there. 

Kay McKenzie Cooke was born in Tuatapere and grew up in Orepuki, a stone’s throw from Gemstone Beach. She was the oldest of the seven children in her family. Through her mother’s line, she is tangata whenua and of Scottish and English descent. Through her father’s line, she is of Scottish and Irish descent. She writes: “My maunga/mountain, the Takitimu range, my awa/river is the Waiau, Southland, my ancestor is Moitoitoi, the maraes I affiliate to are Waihopai, Aparima and Hokonui. My iwi is Kai Tahu, my hapu is Kati Mamoe.”

Kay McKenzie Cooke. Source: https://bellamysatfive.wordpress.com/the-poets/kay-mckenzie-cooke
The McKenzie farm at Orepuki, Princess Range in the background, Te Waewae Bay to the left. Source: https://bellamysatfive.wordpress.com/the-poets/kay-mckenzie-cooke
The view at Orepuki from where Kay used to live. Source: http://andbottlewasher.blogspot.com/2014/04/theres-life-in-old-girl-yet-orepuki.html
Otama Valley. Source: https://kaymckenziecooke.com/2018/08/05/waikaka-visit

When she was ten years old, Kay’s family moved to the Otama Valley, further north in Southland, 20 miles from Gore, where her father continued to work in farming. Five years later, Kay’s father died suddenly and unexpectedly of a heart attack. Her mother took Kay and her siblings to live in Gore. After four years as a pupil at the small, two-roomed, country school of Wendon, Kay attended Gore High School, probably just a year ahead of myself, although I did not know her. In the early 1970s, both of us went to Dunedin for further study,  Kay to attend Teacher’s College. She became an early childhood teacher, got married, and had children. In the early 1990s, she decided to take up writing seriously. Her poems have since been published in a number of journals and magazines. Her first book of poetry, Feeding the Dogs, was published by Otago University Press in 2002 and won the Jessie McKay Prize for Best First Book of Poetry. Her second book of poetry was Made For Weather (2007) and her third was Born To A Red-Headed Woman (2014).

A description of Feeding the Dogs from the publisher: “This bumper collection of 60 poems is autobiographical and in it Cooke writes about town, landscape, family and everyday life. ‘Feeding the Dogs’ is one of the poems in this book. There are other rural poems, such as ‘I love this farm so much I could pat it’, but Kay Cooke is equally at home writing a well-made poem about lawn bowlers in Queenstown, a family reunion, global warming or biotechnology. Cooke’s work is strong and confident. On top of that, she has a particular southern sensibility that is very appealing and recognizable. Cooke writes that her poems come from the ‘sense of isolation that I felt living on a farm in Otama Valley, with tussock-covered hills and no shops and bus trips to school’.”

One description of Made For Weather includes the following: “The poems contain an array of striking images, developed from Cooke’s exposure as a child and adolescent to the wind-whipped coastline of Orepuki, now a ghost town on the eastern fringe of Te WaewaeBay, near Fiordland. The passing of seasons features in the background of scenes which are dominated by ostensibly contemporary concerns such as a wild and woolly boyfriend, or collecting Toheroa. The poet has a gift for capturing people in day-to-day, incidental situations.”

The following comments by the publisher on Born To A Red-Headed Woman are an accurate description of that book: “Laconic, wry, subtly philosophical, Kay McKenzie Cooke’s new collection carries us from her rural Southland girlhood in the 1950s and 60s to the bitter pressures of adopting out her baby as a teenager in the 1970s, and to her present as grandmother, mother, wife and author. A plain-spoken honesty, a sensitivity to the natural world, a gentle humour, a deep sense of how the richness of our relationships lodges in ordinary rituals and routines: all combine in a quietly moving autobiography.” 

Kay’s first two books are out of print, but can sometimes be discovered in second-hand bookstores. You can buy Born To A Red-Headed Woman here.

Kay has two blogs, Cuttings and Time & Place. You can listen to Kay reading “Sacred Days”, a poem of images of her life as a high school student at Gore High School, a poem published in “Born to a Red-Headed Woman”: “I wrote the poem as a sixty-year old looking back into my own adolescence and its callow bewilderment. My very normal teenage confusion was compounded by the recent loss of my father who had died very suddenly of a heart attack when I was fifteen. His sudden disappearance from our lives had necessitated, for my mother, my six siblings and myself, an immediate removal from the freedom and familiarity of a rural home [at Orepuki] to the weird constrictions of life in a small town, living in a wooden villa with a mailbox on a street next to a lot of other wooden villas with mailboxes.” (Click here for more of Kay’s comments on the poem and here for the full text of the poem.)

Kay has lived in Dunedin for many years now, has retired from teaching,  and participates in and helps to organise Dunedin poetry readings. With Jenny Powell, she forms the poetry performance duo, “J&K Rolling”, taking poetry readings to out-of-the-way places and rural areas in New Zealand. Kay is available to visit schools as part of the Writers in Schools programme. She visited Waikaka School in 2018 as part of this. In February this year (2019), she read and discussed her poem, “some time”, at Knox College Chapel’s opening service – an excerpt from this poem is featured on a sculpture in the College quadrangle: “But this is home./ This place,/ where every season counts/ and under our feet,/ safe ground”. I note this because I was a student resident at Knox College in the early 1970s. In March 2018, Kay and Jenny Powell had a poetry stall at the Owaka Cavalcade Market and Family Entertainment Day.

Kay and Jenny outside Orepuki Cafe. Source: http://whistlestoptours.blogspot.com/2015/06/early-march-2015-saw-j-and-k-rolling.html
Kay McKenzie Cooke and Jenny Powell. Source: https://www.jennypowell.co.nz
Kay’s car parked alongside the school fence when she visited Waikaka school. Source: https://kaymckenziecooke.com/2018/08/05/waikaka-visit/
Excerpt from Kay’s poem, Knox College sculpture. Source: https://kaymckenziecooke.com/2019/03/11/one-fine-fine-day
Kay and Jenny’s Owaka Poetry Stall. Source: https://kaymckenziecooke.com/blog-2/

Stones are part of Kay’s childhood memories of Orepuki, and she often visits the beach when she returns there. “I remember as a kid keeping on our bedroom window sill, jam jars full of water to keep my stash of gemstones bright and colourful – until an algae-green sludge smothered their attraction and I had to throw them out again, allowing the rain and air to keep them instead” (from a  2011 blog post).  Her father was born in Orepuki and “over his many years there – long before Gemstone Beach was famous or even called by that name – he, like all Orepuki kids, collected the coloured pebbles”. All of his stone collection then went into the wet cement of the concrete paths and steps he built around their house. Many years later, Kay managed to retrieve the two steps and take them to Dunedin. She comments in the same 2011 blog post:  “I love this tangible reminder I have of of my childhood home. I always feel close to my father (dead 43 years this Thursday) whenever I take time to sit on them and rub my palms over the smooth, rounded stones. To me they are gems not so much semi-precious, as fully-precious. Each one tells a story and recently I’ve been paying attention.” Her poem “living stone” contains the story of the steps, and three other poems were inspired by her father’s Orepuki stones, including “quiet life“. Other poems have been stone-fed, such as “a heart-shaped one“.

Orepuki beach stones in concrete steps, done by Kay’s father, rescued from her old Orepuki home. Source: http://andbottlewasher.blogspot.com/2011/10/stories-written-in-stone.html
Collected from Gemstone Beach by Kay and her son, April 2019. Source: http://andbottlewasher.blogspot.com/2019/04/now-that-family-have-left-our-shores-to.html
The wind-bent trees of Orepuki, another significant landscape feature. Source: https://kaymckenziecooke.com/2018/05/20/fine-balance/

It was a moving experience for me to read Kay’s poems, their power lying in our shared southern roots as well as her personal openness and perceptive insights about everyday life. The links to Orepuki and Gemstone Beach led me to offer Kay the gift of a few of my polished stones from Gemstone Beach, which she was delighted to receive. These stones are the subject of my next Post, 16 Gems – Stones for Poetry.

“Little Things” – The Value of Small Stones

In the sweetness of friendship let there be laughter and sharing of pleasures. For in the dew of little things the heart finds its morning and is refreshed (page 66 of Khalil Gibran, 1923, “The Prophet”).

The “treasure chest” is constructed from brown cardboard.
The 50 little stones in the treasure chest

I recently gave a small “treasure chest” of polished stones to a friend for her birthday. I filled it with 50 little stones, many of them not much larger than one of my fingernails. The stones are from the beaches of the south coast of Southland, mainly from Riverton and Gemstone Beach. Within these 50 are a wide range of the types of stones to be found on these beaches.

Walking along the beach, head down, alert for interesting stones, my eye is often caught by a flash of bright colour belonging to a small stone. At the beginning of my tumble-polishing passion, I collected a lot of such small stones but soon adjusted my eye to pay more attention to larger ones. The smaller ones get even smaller throughout the polishing process. The larger ones promise much more, can be tumbled longer, can be shaped more to remove imperfections and cracks and pits, and are more commanding with their polished presence. So, for a while, I disciplined myself NOT to pick up the smaller stones that caught my eye.

It is also the case, however, that a good mix of different sized stones in a tumble barrel is the ideal. The larger stones need smaller ones to make the process of wearing and shaping more effective. The small stones “carry” the grit or polish to the larger stones, fill up the spaces between them, and balance the load.

Contents of a 3lb barrel of polished stones collected on Riverton beaches
Stones of different sizes from Birdlings Flat
Batch of tumbled stones from Gemstone Beach

Furthermore, some small stones are striking in their pattern or colour or shape, and are valuable in their own right as interesting and beautiful stones. So, now, I allow myself to collect stones of many sizes and do not neglect the smaller ones.

I numbered each of the 50 stones in the birthday “treasure chest” (see photo below, left) and provided a list of the types of stones they were, if I knew.

The 50 stones, numbered
Close-up of some of the little stones

Included were hydrogrossular stones (#8, #31 and possibly #46), stones with fossilised warm casts or traces (#17 and #49, also maybe #29), a pink rhodonite stone (#1), various quartzites (#18, #35, #38 and #45), smoky quartz (#28), a porpyry (#3), andesite (#13), banded rhyolite [now identified as ignimbrite](#22), other rhyolites (#5, #10, #12 and #23), pink granite (#26), jasper (#7, #9, #21, #30, #40 and #43), breccia (#32 and #39), quartz (#34) and argillite (#15, #20, #47 and #50).

Enjoy the little things, for one day you may look back and realize they were the big things (Robert Brault).

A Three Pound Barrel of Polished Stones from Riverton

Today a 3lb barrel of stones collected from Riverton beaches last year finished the tumble-polishing process. Altogether, 46 stones came out of the barrel, some with the odd blemish, but many in excellent order, well polished and free from chips and cracks.

Polished stones from Riverton
Riverton stones
Riverton stones polished
Stones from Riverton beaches

Some of these stones are impressive on both sides:

Some are colourful and bright:

Others are more muted, darker, but nonetheless fascinating:

Pre-Polished Batch of Gemstone Beach Stones – Comments on Pre-Polishing

This batch of 64 stones have just been tumbled in a 4lb barrel with tin oxide “pre-polish” powder. This type of tumble is sometimes seen to be optional, with many stone collectors/polishers simply moving straight to the final “pro-polish” tumble once the stones have been smoothed with a fine silicon carbide grit (e.g., 320 or 400 mesh). However, it has become more common for this stage to be included. [Up-Date 2021: My supplier no longer stocks Pre-Polish tin oxide so I am moving to a one-stage polish approach – see this Post for more information.] 

For the “pre-polish” stage, I use a tin oxide powder of 5 microns.  A “micron” is an abbreviation for a “micrometre”, or a millionth of a metre, that is, one-thousandth of a millimetre (about .00004 inches). A human hair is, on average, about 75 microns across. Other media can be used for pre-polishing. For example, Steve Hart in his “Modern Rock Tumbling” (2008), reports that he uses 1000 mesh silicon carbide grit which is 4.5 macrons in diameter (page 39). [320 mesh silicon carbide grit is about 29 microns, according to the Washington Mills website.]

The aim of the “pre-polish” stage is to produce a smoother stone than possible with coarser tumbling media. I follow the recommendations that came with the tumbling material I bought from the Rotorua Rock and Gemstone Shop. These are to tumble stones in “pre-polish” powder for between three and five days (note that this is for less than the one week or more recommended for all other stages). “Pre-polishing” assists with the final “pro-polish” stage. After “pre-polish”, the stone is not yet glossy and shiny but is very smooth.

Why are Hydrogrossular Garnets found in Nelson and Orepuki?

At the end of my first Post in this series, What are Hydrogrossular Garnets?, one of the questions I raised was why hydrogrossular stones are found in New Zealand primarily in two regions more than 400 kilometres apart, in the Nelson area as well as around Orepuki, at the top and bottom of the South Island. [Writing in May 2021: As explained at the end of this Post, it has been suggested that hydrogrossular garnet can also be found on the West Coast of the South Island, and maybe also in the North Island. July 2022: I have also seen a report of hydrogrossular garnet being found on a beach in Napier.]

I have come to associate hydrogrossular stones with Gemstone Beach at Orepuki because they are not found anywhere else on the southern coast. I have heard third or fourth hand of someone who found one on a Riverton beach but the point of that story was how unusual this was. I have spent more time on Riverton beaches than Gemstone Beach but have found hydrogrossulars only on Gemstone. [Writing in May 2021: Over the past couple of years I have found a couple of small hydrogrossular stones on the Back Beach at Riverton.] Sources of information such as Te Ara The Encyclopedia of New Zealand often mention only Gemstone Beach as where you can find them in New Zealand.

When I undertook more careful research on hydrogrossular garnets it came as a surprise that the area around Nelson was treated as a key source area.  In the entry on “Hydrogrossular” in “A Photographic Guide to Rocks and Minerals of New Zealand” by Nick Mortimer, Hamish Campbell and Margaret Low (2011), it is noted that the world’s first occurrence of the rock was described from the Nelson-Dun Mountain area by Colin Hutton in 1943 (more on this in a later Post). It does go on to note that hydrogrossular can be found on Gemstone Beach as well as in the streams and rivers east and south of Nelson city.

Photographic Guide p34 bottom [Note: May 2022 – This next paragraph often refers to “grossular” rather than “hydrogrossular” garnet, but the two are not the same. I am at present unsure whether Thornton’s comments refer only to “grossular”.] Jocelyn Thornton, in “The Field Guide to New Zealand Geology” (2003), reports that “grossular garnet” can be found in the Dun Mountain area, “found in translucent green masses that can be polished” (page 69), as well as in the Roding, Lee and Maitai Rivers in Nelson (see first photo below for Thornton’s geological map of Nelson area). She points out that rodingite, a rock named after the Roding River, a mixture of grossular and diopside or diallage, can also be found in Cascade Creek in the Eglinton Valley near Milford Sound (see the second photo below, from Te Ara The Encyclopeida of New Zealand). “From there the grossular garnet makes its way through the lakes and down the Waiau [River], being tumbled into the rounded pebbles that can be found with a little effort on Orepuki Beach” (page 70). A 1969 research paper by J. G. Williams at the Department of Geology at the University of Otago had identified hydrogrossular in rocks in the area around Cascade Creek in the Eglinton Valley. Thornton’s book includes a photo of hydrogrossular from the Nelson and Orepuki areas (Plate 1E, opposite page 136 – see third photo below). Riverton Museum has a sample of hydrogrossular from the Eglinton Valley (see fourth photo below). In a  2018 “Southland Times” column (second item), local journalist Lloyd Ester reports: Southland’s Gemstone Beach has the best assortment of unusual pebbles in New Zealand. A combination of ocean currents, shape of the coast and the proximity of the Waiau River – the source of many of the stones – means that the rarities are concentrated along a short strip of beach. The best known of the “gemstones” are grossular garnets which are distinguished by their gloss and weight.” Nevertheless, the Waiau River is relatively young, in geological time. For instance, Thornton presents a map of what the Western Southland-Fiordland area would have looked like about 50 million years ago, the Waiau Valley being under sea (see fifth photo below). It’s possible that some of the hydrogrossular rock that became pebbles on Gemstone Beach were swept there by ocean tides millions of years ago.  

Jocelyn Thornton (2003), “The Field Guide to New Zealand Geology”, page 67
Jocelyn Thornton (2003), “The Field Guide to New Zealand Geology”, Plate 1E
Hydrogrossular garnet from the Eglinton Valley, Riverton Museum
Jocelyn Thornton (2003), “The Field Guide to New Zealand Geology”, page 155 – I have circled in red the approximate location of present-day Orepuki

To return to the question being examined in this Post: Why are hydrogrossular stones found in New Zealand primarily in two regions more than 400 kilometres apart, at different ends of the South Island? This distribution is not random but is in fact part of a much larger pattern. The first map below, found in a Google image search, shows that the sequence of terranes in Fiordland, Southland and Otago is repeated in Nelson and Marlborough. A “terrane” is a floating bit of the earth’s crust that butts up against a continent (New Zealand is part of the Zealandia continent, much of which is under water – see second map below). This disjunction in the terranes leads to the idea of there being western and eastern geological provinces making up the South Island (see third map below, from a 2013 article in “Gondwana Research”).  New Zealand consists of at least 10 terranes (see pages 41-42 of Peter Ballance’s, 2017, “New Zealand Geology: An Illustrated Guide”  for a list and description). But these have been partially rotated and then split by the Alpine Fault. As shown in the map by Jocelyn Thornton (fourth map below), the rocks (terranes) demonstrate that Northwest Nelson and Fiordland were once together. The two sources of hydrogrossular garnets may be 400 kilometres apart now but they are in the same terrane and 25 million years ago were in the same locality.  

Terranes of the South Island. Source: http://cires1.colorado.edu/people/jones.craig/NewZealand/NewZealandFigs.html
Continent of Zealandia. Source: https://teara.govt.nz/en/map/8282/the-new-zealand-continent
Western and Eastern Geological Provinces of the South Island. Source: https://www.researchgate.net/figure/Map-of-New-Zealand-showing-Western-and-Eastern-Provinces-separated-by-the-Median_fig1_259521484
Jocelyn Thornton (2003), “The Field Guide to New Zealand Geology”, page 34

The Alpine Fault runs for about 600 kilometres along almost the entire length of the South Island. It is a segment of the boundary between the Pacific Plate and the Australian Plate (see map below, from Wikimedia). The Southern Alps have been uplifted on the fault over the last 12 million years in a series of earthquakes. However, most of the motion on the fault is sideways, with the Tasman district and West Coast moving north and Canterbury and Otago moving south. Horizontal movement of the Alpine Fault is about 30 metres every 1,000 years, which is very fast by global standards. Each time it has ruptured, it has also moved vertically, lifting the Southern Alps in the process. GNS Science estimates that in the last 12 million years the Southern Alps have been uplifted by  20 kilometres, and it is only the fast pace of erosion that has kept their highest point below 4,000 metres. Glaciers and rivers have removed the rest of the material and spread it out across the lowland plains or onto the sea floor (and beaches!). The Alpine Fault was not recognised until 1941 because the area was rugged and isolated, and earlier generations of geologists did not have the advantage of having an aerial view.

Source: https://commons.wikimedia.org/wiki/File:NZ_faults.png
Source: https://visibleearth.nasa.gov/view.php?id=67355
Source: https://teara.govt.nz/en/photograph/8204/the-alpine-fault

In conclusion, hydrogrossular garnets are found primarily in two regions in the South Island more than 400 kilometres apart because of the way that the Alpine Fault has split whole terranes of rocks and moved them sideways, south to north. [Writing in May 2021: A reader of this Blog has told me he has found what he thinks is a hydrogrossular stone in a West Coast river. This is the first time I have heard of a West Coast location, but it makes sense if hydrogrossular rock “travelled” north along with the Alpine Fault. On the way, rivers could certainly have moved stones away from the fault. The reader also suggested that hydrogrossular garnet can be found in the North Island.]

The next Post in this series looks at how hydrogrossular garnet is one of 13 minerals that were first described in New Zealand. 

Information on the four photos at the top of this Post:

First photo: A sample of hydrogrossular garnet from the Eglinton Valley, in a drawer of rock samples in the Riverton Museum, Te Hikoi.
Second photo: A compartment of hydrogrossular stones and at least one quartz stone, from my own collection of polished stones.
Third photo: Handful of hydrogrossular garnets from Gemstone Beach, on page 155 of “The Story of Murihiku/Southland – A synopsis: An overview of Southland’s Heritage” by Russell Beck, Cathy Macfie and Lloyd Esler, April 2007 https://docplayer.net/57903929-The-story-of-murihiku-southland.html
Fourth photo: Rodingite rock sample, from Te Ara The Encyclopedia of New Zealand https://teara.govt.nz/en/photograph/9077/rodingite

Why are Hydrogrossular Stones Called Garnets?

These four photos are of hydrogrossular garnets discovered on Gemstone Beach, near Orepuki (the last two photos are of the two sides of the same stone). They don’t look like garnets, do they? We are used seeing garnets like this:

natural-red-garnet-stone-drop-earrings
Source: https://www.aliexpress.com/item/natural-red-garnet-stone-drop-earrings-925-silver-Natural-gemstone-earring-women-generous-fashion-drop-Earrings/32789404123.html

The word “garnet” comes from the 14th‑century Middle English word “gernet”, meaning “dark red”. It is thought to be derived from the Latin “granatus”, from “granum” (meaning “grain, seed”), and possibly a reference to “pomum granatum”, the pomegranate, a plant whose fruits contain abundant and vivid red seed covers which are similar in shape, size, and colour to some garnet crystals. In fact, garnets can be found in a wide range of colours, although red is the most common.

In a previous Post, What are Hydrogrossular Garnets?, it was noted that the chemical composition of hydrogrossular garnets is hydrous calcium aluminium silicate and that hydrogrossular garnets hardly ever occur as good crystals but rather as dense masses. This Post aims to explain why hydrogrossular garnets are called garnets and why they are not crystals.

Stones are made up of at least one mineral, often more. A mineral is a solid chemical compound that occurs naturally in pure form. These ideas have led to the view that rocks are to be officially named and identified by means of a scientific description of, among other things, the chemical make-up of their constituent minerals. (Other things that help to identify minerals include hardness, “specific gravity” meaning density, “lustre” or how it reflects the light, “cleavage” meaning its tendency or not to break along smooth planes parallel to zones of weak bonding, and colour.) So what is a “garnet” or not depends on its chemical make-up. I am not a chemist so my understanding, as presented here, is based on what sense I can make of a range of material, some of it quite technical.

In the section on “Garnet” in Geology.com, it is noted that Garnet is the name used for a large group of rock-forming minerals: These minerals share a common crystal structure and a generalized chemical composition of X3Y2(SiO4)3. In that composition, “X” can be Ca, Mg, Fe2+ or Mn2+, and “Y” can be Al, Fe3+, Mn3+, V3+ or Cr3+.

Click on the Table below to see how different types of garnets have different chemical compositions in which the X and Y position for chemical elements vary: 

The Note on this Table (above) points out that “the compositions listed…are for end members of several solid solution series”. In other words, there are gradations in the series of stones we call garnets and when we group them we are breaking up a continuum, creating “end members” at the start and end of each group. “Garnets are a related group of minerals whose chemical compositions can vary continuously from one to the other” (p. 160 in Busbey et al., 2013, “Rocks & Fossils“). There is actually a wide range of types of garnets that are grouped in various ways. Wikigempedia reports that the garnet family is divided into two sub-groups, Pyralspite which is Calcium-free garnet and Ugrandite which is Calcium-rich garnet. Almandine (iron-aluminium silicate), Pyrope (magnesium-aluminium silicate), and Spessartine (manganese-aluminium silicate) are the main members of Pyralspite sub-group, and Grossular (Calcium-aluminium silicate), Andradite (calcium-iron silicate) and Uvarovite (calcium-chromium silicate) are the members of Ugrandite sub-group.

The excellent article on Garnet in Wikigempedia presents a table which summarises the common properties of all garnets as well as the variations in chemical formulae for three types of garnets: 

We are now able to make a little more sense of the Wikipedia entry on hydrogrossular, mentioned in the previous Post, where it states:

Hydrogrossular is a calcium aluminium garnet series (formula: Ca3Al2(SiO4)3−x(OH)4x, with hydroxide (OH) partially replacing silica (SiO4)). The endmembers of the hydrogarnet family (grossular, hibschite, and katoite) depend on the degree of substitution (x):
grossular: x = 0
hibschite: 0.2 < x < 1.5
katoite: 1.5 < x < 3.

The latter part of this statement is in effect saying that there are slightly different types of hydrogrossular caused by varying degrees of replacement of silica by hydroxide in the stone.  

The Geology.com article points out that garnets in general have a “vitreous [glassy] luster, a transparent-to-translucent diaphaneity [transparency], a brittle tenacity, and a lack of cleavage.” Furthermore, they can be found as individual crystals, stream-worn or beach-worn pebbles, granular aggregates, and/or massive occurrences (“massive” meaning lacking internal crystalline structure).

Wikipedia explains that hydrogrossular is “found in massive crystal habit, sometimes grown in with idocrase [another mineral]”. In terms of its transparency, hydrogrossular is “translucent to opaque”, and can be found in the colours of green to bluish green, pink, white, and gray. The cause of the green color is chromium, and possibly iron. Pink hydrogrossular is caused by the presence of manganese. Hydrogrossular may also have dark gray to black small inclusions.

Wikipedia mentions that hydrogrossular garnet has similarities to jade. This can perhaps be seen in the way in which it can be carved – see Russell Beck’s carvings in Te Ara The Encyclopedia of New Zealand.

I am unsure why hydrogrossular garnets are not clear translucent crystals like other garnets can be. I have not found any explanation for that. My suspicion is that it has to do with their water content, the “hydroxide” component. This might “cloud” the stones in their composition.

The next Post in this series, Why are Hydrogrossular Garnets found in Nelson and Orepuki?, will consider why hydrogrossular garnets can primarily be found in two main regions in New Zealand, the Nelson area and the south-west of the South Island, some hundreds of kilometres apart.

What are Hydrogrossular Garnets?

I first came across reference to hydrogrossular garnets when gathering information online about the stones that could be found on Gemstone Beach, Orepuki, on the south coast of New Zealand’s South Island. Some brief descriptions of Gemstone Beach include comments along the following lines:  “Semi-precious gems such as garnet, jasper, quartz and nephrite can often be found on the beach. A few hours beachcombing could easily yield gems such as hydrogrossular, jasper, fossil worm casts and the elusive sapphire” (quoted from information about the Riverton–Aparima South Coast Heritage Trail. See also Nature’s Edge: Tuatapere and the mindat.org entry on Gemstone Beach.) The source of this description could be a Heritage Trail sign that, to my knowledge, is no longer at Gemstone Beach (I don’t recall having seen it on any of my visits).

Gemstone Beach Heritage Trail
Source: https://talltales.me/2013/02/24/the-south-of-the-south/photo-2-01-13-10-30-21-am

The Encyclopedia of New Zealand mentions hydrogrossular garnets in the following terms:

Calcium-rich garnet is called grossular. A red form, found in South Westland, is known as hessonite. Another variety, containing some water, is called hydrogrossular and was first identified at the Roding River near Nelson. It is also found on the beach near Orepuki in Southland. Rounded lumps of pale green hydrogrossular take a good polish and have been used for jewellery.   Hydrogrossular pebbles, being heavy and exceptionally hard, were used by Southland Māori as hammer stones for the making of stone implements

In many ways, all this information raised more questions for me than it answered. What does a hydrogrossular garnet look like? Is it a valuable gemstone, like other garnets? Why is it a garnet? How often can these stones be found on Gemstone Beach?

For a while, I mistakenly referred to them as “hydroglossular” (“…gloss…” not “…gross…”), thinking that because they were likely to be shiny they would be glossy. On my first few trips to Gemstone Beach, I decided that there was a particular stone that was probably a “hydroglossular”, even thought it seemed quite dull. It was a grey stone that was kind of a dull quartz-like thing, looking like there was water within its fabric (the “hydro” part).

For a brief time, I thought this sort of stone could be a hydrogrossular

I collected some and tried polishing them but they were very unremarkable stones.

So what does “hydrogrossular” mean? Wikipedia gives an answer that refers to the physical-chemical make-up of the stone: 

Hydrogrossular is a calcium aluminium garnet series (formula: Ca3Al2(SiO4)3−x(OH)4x, with hydroxide (OH) partially replacing silica (SiO4)). The endmembers of the hydrogarnet family (grossular, hibschite, and katoite) depend on the degree of substitution (x):
grossular: x = 0
hibschite: 0.2 < x < 1.5
katoite: 1.5 < x < 3.
Hydrogrossular is a garnet variety in which a Si4+ is missing from a tetrahedral site. Charge balance is maintained by bonding a H+ to each of the four oxygens surrounding the vacant site.

So the “hydro” refers to “hydroxide”. Consulting Wikipedia again, hydroxide consists of an oxygen and hydrogen atom held together by a covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. (I will comment on other aspects of the above physical-chemical description in the next Post in this series.) 

If you look up “grossular” in Wikipedia, you discover that “the name grossular is derived from the botanical name for the gooseberry, grossularia, in reference to the green garnet of this composition that is found in Siberia”. 

It wasn’t until someone I met on Gemstone Beach about a year ago showed me some hydrogrossular stones he had just picked up, and actually gave me a couple, that I realised what they looked like and, just as importantly, what they felt like. They feel waxy, not the same kind of smoothness as a quartz stone, which is cool to the touch in contrast to the more “warm” feel of a hydrogrossular.

The Riverton Museum, “Te Hikoi”, has a small room which displays stones from the area, linked to an exercise of stone collecting set up for children on holiday. It includes a few hyrdrogrossular stones. With the permission of Museum staff, I took some photos of the display and of the drawers of rock samples in this room.

Riverton Museum, children’s rock collection display
Riverton Museum, children’s rock collection display
Hydrogrossular garnet stones in Riverton Museum, children’s rock collection display
Riverton Museum, drawers of rock samples
In one of the drawers in the rock display room, Riverton Museum
Hydrogrossular garnet, Riverton Museum

The Southland Museum in Invercargill, now closed due to problems with Earthquake strengthening, had a Minerals display which included a non-smoothed rock of hydrogrossular garnet. 

Hydrogrossular garnet, Minerals display, Southland Museum, Invercargill
Minerals display, Southland Museum, Invercargill
Southland Museum, Invercargill. Source: https://www.stuff.co.nz/national/102942792/southland-museum-and-art-gallery-building-closed-because-of-earthquake-risk
Tuatara statue, with petrified wood in background, sited outside the entrance to the Southland Museum, Invercargill

On page 34 of the excellent “A Photographic Guide to Rocks and Minerals of New Zealand” by Nick Mortimer, Hamish Campbell and Margaret Low (2011) is an entry on “Hydrogrossular”: 

Five key points made in this entry are:

1) Its chemical composition is hydrous calcium aluminium silicate.  

2) Hydrogrossular garnet hardly ever occurs as good crystals but rather as dense masses.

3) It can be found in the Nelson area as well as around Orepuki.

4) It is one of 13 minerals first described in New Zealand. 

5) It was first identified by Colin Hutton in 1943.

In the next Post in this series, Why are Hydrogrossular Stones Called Garnets?, I will look at the first two points. Later Posts include Why are Hydrogrossular Garnets found in Nelson and Orepuki? and What is Hydrogrossular’s Place Among the Thirteen Minerals First Described From New Zealand?  Also see Hydrogrossular Garnet on TumbleStoneTwo. Three significant later Posts on hydrogrossular garnets are February-March 2022 Fossicking Trip: Stone of the Day #15, Hydrogrossular Garnet from Gemstone Beach and February-March 2022 Fossicking Trip: Stone of the Day #19, Big Gemstone Beach Hydrogrossular Garnet and January 2022, Stone of the Day #20 – Brown Hydrogrossular Garnet from Gemstone Beach.  

A Batch of Polished Stones from Riverton’s Back Beach

Panorama of Riverton’s Back Beach – Bluff Hill in the middle far distance, Stewart Island/Rakiura to the right, in the mist on the horizon, across Foveaux Strait
The 78 polished stones in a plastic storage container

These 78 stones were collected from the Back Beach in March 2019. They were initially tumbled in 320 grit as they were smooth beach pebbles. They were then tumbled in pre-polish and pro-polish tin oxide and burnished in borax. Altogether, these stones were processed  in a 4lb rubber barrel for four weeks. 

78 polished stones collected from Riverton’s Back Beach in March 2019, set out just having been dried from the opened barrel

Each stone has its own interest and attraction. The following are some of the most intriguing (Note: Some of the close-ups have been manipulated a bit to explore the patterns and colours):

 

 

The Back Beach at Riverton faces Stewart Island, some 40 kilometres away across Foveaux Strait, a rough and often treacherous stretch of water. The powerful waves are ideal for smoothing stones as they are tossed back and forth and up and down the beach. 

Back Beach, Riverton, from the hill separating it from the Beach Past the Back Beach
On the Back Beach, looking back to the hill from which the previous photo was taken
The incoming wave dislodges stones, tossing them in the air and pushing them up and down and along the beach
The amount of stones on the beach varies considerably – in March 2019, a high bank of stones had been cut into in scallop shapes by the waves
The stones here are generally much smaller than the ones to be found near McCracken’s Rest, closer to the Waiau River mouth. Further up the beach, larger stones the size of your palm, can be found
Birds on the Back Beach stones