A Blog About Stone Gathering, Tumbling and Polishing, and Rocks and Landscapes, from New Zealand – With Musical Interludes (john.tumblestone@gmail.com)
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:
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
For a number of years before I retired from the University of Waikato, I assisted with the supervision of Gemma Piercy-Cameron’s PhD thesis. Gemma was finally successful in completing her grand project, Baristas: The Artisan Precariat, a few months ago. Currently, Gemma is a Lecturer in Sociology and Social Policy at the University of Waikato (see her Staff Profile). I presented her with nine milestones to mark her accomplishment.
The following letter accompanied Gemma’s milestones (photos added here):
Why Nine Stones? Nine is seen to have philosophical significance, due to its unique numerical attributes. In the Hebrew tradition, for instance, Nine represents truth, since it reproduces itself when multiplied. Multiply any number by 9, then add the resulting digits and reduce them to a single digit, it always becomes a 9 again, e.g., 6 x 9 = 54, 5 + 4 = 9; 23 x 9 = 207, 2 + 0 + 7 = 9. Another attribute of Nine is that when added to any other number and then that number is reduced to a single digit, it always comes back to itself, as if nothing was added at all. For example, 5 + 9 = 14, 1 + 4 = 5; 7 + 9 = 16, 1 + 6 = 7. Nine is the Triple Triad, consisting of three times three, and so is seen as symbolic of completion, fulfillment, attainment, the beginning and the end, the ultimate whole number. Appropriate to recognise the completion of a PhD!
Stone #1 “Coffee”
Stone 1 “Coffee”
Other side of Stone 1 “Coffee”
Unknown type, collected at Riverton (Southland) July 2017, polishing completed September 2017. Polishing brought out the creamy swirl that reminded me so strongly of coffee and latte art that I knew it was destined for you.
Back Beach, Riverton, Stewart Island in background (left)
Western end of Back Beach, Riverton
Gull and stones, Back Beach, Riverton
Stone #2 “Positioned Sparkle”
Stone 2 “Positioned Sparkle”, full of quartz and large mica crystals
Same face of Stone 2 “Positioned Sparkle”
Reverse face of Stone 2 “Positioned Sparkle”
Detail of some of Stone 2’s large mica crystals
Mica-rich pegmatite rock, collected at Joyce Bay (near Charleston, Buller District) March 2017, unpolished. Your thesis reflects who you are, and sparkles as it is turned to be viewed from different positions. Different things will be seen in it depending on who views it from which position.
Joyce Bay on left – from a postcard
Source: Google Maps
Northern end of beach at Joyce Bay, where Stone 2 was found
Joyce Bay rock, full of quartz and mica
Joyce Bay, near Charleston, West Coast
Stone #3 “Effort”
Stone 3 “Effort”
Stone 3 “Effort”
Detail of Stone 3 “Effort”
Mudstone, collected at Riverton July 2017, polishing completed September 2017. This stone started millions of years ago as a number of sediment layers, being compressed by weight and heat. Your thesis consists of layers of effort and activity, building on each other, one layer being the foundation for the other. Over time, effort becomes more focused, refined, productive, until completion is reached.
Henderson Bay, Riverton
Stone #4 “Complexity”
Stone 4 “Complexity”
Detail of Stone 4 “Complexity”
Detail of Stone 4 “Complexity”
Stone 4 “Complexity”
Jasper, with silica, collected at Riverton February 2018, polishing completed August 2018. Reality is complex and resists analysis. Analysis is hard labour.
Stone #5 “Depth”
Stone 5 “Depth”
Detail of Stone 5 “Depth”
Detail of Stone 5 “Depth”
Stone 5 “Depth”
Pale green Quartzite, collected at Orepuki (Southland), April 2016, polishing completed November 2017. Depth of understanding and insight is gained by multi-method qualitative research.
The beach near Orepuki
The beach near Orepuki
Stone #6 “Found Worthy”
Stone 6 “Found Worthy”
Stone 6 “Found Worthy”
Stone 6 “Found Worthy”
Stone 6 “Found Worthy”
Stone 6 “Found Worthy”
Detail of Stone 6 “Found Worthy”
Banded Agate, collected on Birdlings Flat (Canterbury) June 2016, polishing completed September 2016. Agate is formed from quartz crystals growing in layers so small they can barely be seen. The layers build up to fill cavities in sediments left by gas bubbles in volcanic rocks. This particular banded agate is very unusual (the only one of its kind I have found) – when held up to the light, it is apparent that the bands are not smooth but have intricate and delicate lace-like waves in them. This stone will have originated in the Alps, been washed down a Canterbury river, and swept along the coast to be deposited on Birdlings Flat which abuts Banks Peninsula. Your thesis has survived close examination in the light of others’ assessments, and has been found to be worthy of scholarly esteem.
Birdlings Flat beach, the western part of Kaitorete Spit abutting Banks Peninsula
Kaitorete Spit, a 25 kms long gravel bank, looking towards Banks Peninsula, separating Lake Ellesmere from the Pacific Ocean
From the car park at Birdlings Flat
Birdlings Flat beach and Banks Peninsula
Stone #7 “Patterns”
Stone 7 “Patterns”
Detail of Stone 7 “Patterns”
Detail of Stone 7 “Patterns”
Stone 7 “Patterns”
Unknown type (possibly a type of schist?), collected at Riverton February 2018, polishing completed August 2018. Research identifies patterns and layers and makes sense of them for others.
Beach Past The Back Beach, Riverton
Beach Past The Back Beach, Riverton
Beach Past The Back Beach, Riverton
Beach Past The Back Beach, Riverton
Beach Past The Back Beach, Riverton
Beach Past The Back Beach, Riverton
Stone #8 “It takes time to construct an interesting story”
Stone 8 “It takes time to construct an interesting story”
The largest fossil worm cast in Stone 8 “It takes time to construct an interesting story”
A smaller fossil worm cast in Stone 8 “It takes time to construct an interesting story”
Detail of Stone 8 “It takes time to construct an interesting story”
Argillite, a hardened mudstone, with fossil worm casts, collected at Orepuki February 2018, polishing completed August 2018. This argillite started as mud under the sea 250-280 million years ago. The interesting linear features were left behind by ancient worms who had ingested lighter coloured mud. All pieces of scholarly writing, including your thesis, are like fossils of your thoughts at a particular period of time, persisting in existence even as you go on to other thoughts and activities.
Gemstone Beach, Orepuki
Gemstone Beach, Orepuki
Stone #9 “Well Travelled and Wide Ranging”
Stone 9 “Well Travelled and Wide Ranging”
Detail of Stone 9 “Well Travelled and Wide Ranging”
Detail of Stone 9 “Well Travelled and Wide Ranging”
Stone 9 “Well Travelled and Wide Ranging”
Quartzite, stained with iron, collected at Budleigh Salterton (Devon, England) May 2018, polishing completed August 2018. These Devon stones are identical to rocks found in Brittany in France. Some 200-250 million years ago, Brittany was mountainous and rivers drained from it northwards across the Triassic desert, across what was to become the English Channel. The quartzite rocks were tumbled into pebbles and eventually deposited as pebble beds outcropping on cliffs at the beach of Budleigh Salterton village. Good PhD research takes time, has gone places, and has a broad base of experience and reflective thought.
Just out of a 3lb borax burnishing tumble, 43 newly-polished stones from a Riverton beach.
I collected these stones at a beach I call the “Beach Past the Back Beach” at Howells Point, Riverton, in March 2019. When you reach the end of the road at Howells Point, there is a track up the sand dunes. Down the other side is this beach, which stretches for maybe 900 metres further westwards. Many of these stones were found at the far eastern corner, the area circled in this photo:
Riverton’s “Back Beach” is the stretch along the last part of the road that winds along the coast. If you walk over the dunes from there, you come to the “Beach Past the Back Beach”.
These are not particularly spectacular stones, though some are really interesting. Not all have polished perfectly, some have scratches and holes in them, but I polished them because of their intriguing colours and patterns.
Photos of a selection of these newly-polished stones:
This is the 13th Post in this series on the tumble-polishing of 40 Riverton stones, going through each Stage from stone collection on the beach through to the final polish and burnishing. The first Post in the series can be found here.
The previous Post examined how Stones 1 to 5 came through the tumble-polishing process. This Post looks at Stones 6 to 10, giving consideration to how well they have polished:
Stones 6 to 10, rough, as collectedStones 6 to 10, after polishing
STONE 6
Stone 6 is the type of stone that shows its character only upon tumbling. When rough and dry, it is unremarkable and inauspicious. Upon smoothing and polishing, its lovely patterns and grain become clearly apparent. There are some breaks in the surface of the polished stone, including chips at one end and on both edges. In all such instances, shiny mica crystals can be seen at the bottom of the chips. I had previously noted that one of these chips occurred during the Pre-Polish tumble, and the others would have been the result of the Pro-Polish and Borax tumbles. They would have been caused when other stones bumped into this one in the barrel, even though I used a lot of plastic beads at these Stages. Tumbling again in 100, 220 and 320 grit might erase these chips but might cause others. The stone has a slightly brittle character – maybe its metamorphism was too brief to bind all the constituents together tightly.
Stone 6 polished
Stone 6 polished
Close-up showing coarse grained foliation of Stone 6
At one end of Stone 6 is this chip
Under the chip in the previous photo is a cluster of small mica crystals
Another chip in the side of Stone 6
I have always felt that it is very difficult to guarantee a good smooth polish with this type of stone, though it is possible on very rare occasions and I have done it.
Stone 6 is a foliated metamorphic stone, somewhere along the schist-gneiss continuum. As a source on metamorphic rocks puts it: “Schist is a high degree of metamorphism, characterized by coarse grained foliation and/or lineation, with mica crystals large enough to be easily identified with the unaided eye. Gneiss is a medium to coarse-grained, irregularly banded rock with only poorly developed cleavage. The light and dark bands (gneissic banding) are alternations of felsic vs. mafic layers.” Based on grain size and type of banding, my guess is that Stone 6 is gneiss, while the stone below (which I recently collected on the Back Beach at Riverton and which has gone through a 320 grit tumble) is probably schist.
Probably a schist stone, just out of 320 grit tumble
Detail of stone’s grain
STONE 7
This is a gorgeous green mudstone, probably argillite, that has polished without blemish. From the wearing away of the surface, a broad light-coloured stripe has been revealed. This is in fact what is commonly referred to as a “fossilised worm cast”, left behind millions of years ago as a worm-like animal maybe crawled through mud, ingested material and then excreted it. As sediment layers have piled on top over many many years, and weight and heat built up, the process has turned mud and worm cast into rock.
Stone 7 polished, fossil worm cast apparent
Stone 7 polished.
Detail of fossil worm cast
Detail of Stone 7
Fossil worm cast stones can readily be found on Riverton beaches though they are more often associated with Gemstone Beach, near Orepuki, 30 kilometres away. (See later Posts on these types of stones and trace fossils.)
STONE 8
This green stone has also polished well, with only one small area that is not completely smooth.
Stone 8 polished.
Stone 8 polished.
Close-up of Stone 8.
Close-up of Stone 8
There are a lot of green stones like this on southern beaches, some of them argillite (which I don’t think this one is), many with interesting patterns in them. They usually polish well.
STONE 9
After the initial tumble in 100 grit (Stage 2), I recorded that Stone 9 had a medium sized pit in its side. After the 220 grit tumble, the pit remained. I would normally have considered discarding the stone at this point, but for the sake of this series of Posts, following these 40 stones from rough to polish, I continued with it. After the 320 grit tumble, I noted there was some smoothing out of the pit, but it remained.
Stone 9 is a breccia, a type of stone where small angular fragments of (a diversity of) rocks are cemented together in a fine-grained matrix. As John Farndon puts it on page 95 of The Complete Illustrated Guide to Rocks of the World (2012), these sharp-edged fragments were caught up in the matrix before there was any time to round off the rough edges. The pit I had noted is in effect one of these fragments sunken below the surface of the stone, probably because it is softer and has worn away more quickly than the rest of the stone (similar to Stone 4, as noted in the previous Post). However, generally speaking, most of Stone 9 has polished well:
Stone 9 polished
Stone 9 polished
The main issue when polishing a breccia is whether all the various fragments will wear away at the same rate and whether they will all polish. The original pit is much shallower now but it is readily felt when a thumb is rubbed over it.
The side of Stone 9
The shallow pit on the side of Stone 9
In the course of polishing, two other fragments in the breccia have failed to polish as a result of their relative softness:
On the same side of Stone 9…
…two other fragments that have failed to polish
STONE 10
This is another breccia, and it has polished quite well.
Stone 10 polished
Stone 10 polished
Detail of Stone 10
From the outset of tumbling, however, it has had a small but relatively deep hole in it, where maybe a small fragment has become dislodged. When inspecting it after the 320 grit tumble, I noticed that a couple of small indentations had also become apparent, probably where softer stone fragments had worn away a bit more quickly than the rest of the stone.
The hole in Stone 10
Two softer parts of Stone 10 that have not polished
Breccia stones are always interesting, because of the diversity of colour and shape of the embedded fragments. Many of them can be found along the southern coast.
Stones 11 to 15 are dealt with in the next Post in this series.
Since I got back home from Southland at the end of March, I have been tumble-polishing stones collected from Gemstone Beach near Orepuki (see here for an account of their collection). On 28 April the polishing process finished for one 4lb barrel containing a mix of different types of interesting and colourful stones. These are the subject of this Post.
These stones are not “gems” in the sense of precious and sparkling jewel-like stones such as diamonds and sapphires. But I actually find them to be much more interesting and intriguing, many of them a mystery as to how they got the way they are. In this sense they are the true gems of Gemstone Beach.
This batch of 95 Gemstone Beach stones started their tumbling in 320 grit and then were tumbled in pre-polish and pro-polish tin oxide before a final week in a burnishing tumble with borax. This is how they ended up:
95 Gemstone Beach stones just out of the final Borax tumble
To look at some of these stones more closely…
One of them is a gorgeous quartzite (my identification of it as a quartzite is based on what I learned at Vince Burke’s Museum at Birdlings Flat):
Quartzites are not as common along the south coast as at Birdlings Flat in Canterbury, but I always find a couple of excellent ones at Riverton and Orepuki. They polish well, often have great colour, have interesting veins through them, and there’s a depth to them that makes them intriguing.
Two of the stones look like marble. Again, I can usually find one or two such stones on a collecting expedition, and I have started to keep an eye out specifically for them:
Marble-looking stone #1
Other side of marble-looking stone #2
Patterns in marble-looking stone #2
Marble is limestone subjected to heat and pressure. Veined and patterned marble is often created when a pure white original marble is cracked or shattered and the spaces between the fragments are filled with other materials. As I noted, I don’t know whether these stones are marble or not, but they certainly remind me of it. Note: April 2025 – These stones are indeed NOT marble but are iron-stained quartz. They tumble polish well and often have interesting patterns.
Over the last three years, I have found maybe half a dozen stones like this one:
I have always suspected that they are petrified wood. However, I am beginning to wonder whether they are in fact a type of jasper. I have always found them in association with dark red jasper stones, at Waikaka and on the south coast, and sometimes paler forms of jasper have been nearby. They don’t have the obvious characteristics of petrified wood, like wood grain, but it has been their light brown colour that seemed wood-like. And they have a brittleness like jasper has. Irrespective of what they are, I like them. Note: April 2025 – These stones are indeed jasper, not petrified wood.
This next stone has a very unusual set of linear features:
It could be quartz with inclusions of some other mineral. Another stone with a different kind of “inclusion” is this small green one which has specks of pink:
The next four stones have various kinds of fascinating patterns. The first stone has a breccia section at the top. The second stone is about three-quarters red with various small inclusions. The third has alternating light and dark layers plus a white halo. The fourth is actually one of my three or four favourites in this group of 95, due to its patterns of shades of grey (the last four photos below are of this stone, and they do not do it justice).
One of the most unusual stones I picked up off Gemstone Beach in March is this one:
I think these are coral fossils in this stone. I have not done much reading on fossils but I have been recently been going through a book which I found in my local library, “Rocks and Fossils” by Arthur Busbey, Robert Coenraads, David Roots and Paul Willis (2007). On page 211, the authors mention that “corals are among the most common fossils on Earth”. They refer to “rugose corals” whose characteristics could account for some features of the fossils in this stone. Rugose corals have the following structure:
A fossilised coral like this would leave circular impressions of different sizes in a stone, depending how far each individual coral is eroded away from its top. Something like this would account for the patterns on the stone (above) I found on Gemstone Beach. Note: April 2025 – I suspect this stone is not fossil coral but rather an orbicular variety of some rock.
Sometimes I come across stones with pink in them. It is thought that the presence of manganese or cobalt could cause this. For example, rhodochrosite and rhodonite owe their pink colour to manganese, and cobalt ore is often pink. Here are two pink stones found on Gemstone Beach in March: Note: April 2025 – These are thulite.
Finally, five other interesting and colourful stones:
All of these stones illustrate the wide range of stones that can be found on Gemstone Beach that tumble polish well.
DEVELOPMENTS IN MY STONE COLLECTING AND POLISHING STRATEGY
I have become aware that I have changed my approach to collecting and polishing stones over the past three years. Initially, I collected any stone that looked like it might be interesting. I often thought to myself, “Let’s see what happens to this one.” I then tried to produce a completely smooth polished stone, with no flaws. I put each stone through all the stages of tumbling, starting with 100 grade silicon carbide grit. This meant that the stones lost a lot of their material by the end of the process. Along the way, I also discarded stones that had pits or cracks that were not worn away – I was looking for a perfect polish.
More recently, over the past year or so, I have come to collect much more selectively, and I polish with more leniency. When picking up stones on the beach, I now discard many of them even though I know they will polish well. They include, for instance, white quartz and red jasper, excellent examples of which I already have. I aim to collect the most unusual and interesting ones, and the ones that have very few pits or cracks, if any. I then sort through these stones when I return to my accommodation at the beach, dry them and inspect them carefully – flaws show up much more clearly when the stone is dry. I tend to discard maybe one-quarter to one-third of the ones I have collected so the ones I bring home to polish are much more likely to be interesting and to polish successfully. And I can start tumbling most of these stones with 320 grade grit, skipping two stages and saving at least two weeks of total tumbling time.
I am also less severe in judging an acceptably polished stone. I will now be happy with a stone that still has some flaws, that is not completely smooth. This means that I am able to keep a wider range of stone types. Also, the end product will be a bit bigger as it has not been worn away as much. A stone is kept based on its interesting colour or pattern rather than its smoothness.
The purpose of this and the following Posts is to examine how the 40 Riverton stones have emerged from the polishing process and to compare them with how they looked before polishing. The Seven Stages that these 40 stones have gone through are: Stage One, Stone Collection; Stage Two, Silicon Carbide 100 Grit Tumble; Stage Three, 220 Grit Tumble; Stage Four, 320 Grit Tumble; Stage Five, Tin Oxide Pre-Polish; Stage Six, Pro-Polish; and Stage Seven, Borax Burnishing.
This is the 12th Post in this series – the first Post can be found here.
To start with Stones 1 to 5 [Note: The second photo below does not do justice to the shine on the polished stones, due to the artificial lighting conditions under which the photo was taken]:
Stones 1 to 5, rough, as collectedStones 1 to 5, after polishing
STONE 1
Before polishing, Stone 1 (far left) was about 8 cms long and about 5 cms wide at its widest point (using the graph paper under it) and after polishing it has lost perhaps only a few mms of size. I had noted in Post Two of this series that Stone 1 is most likely of volcanic origin, probably rhyolite, as it has small specks in it that would have originally be gaseous pockets. [Note: I have since decided that this stone is ignimbrite, not rhyolite.] After the 100 grit tumble, these small pits were obvious. I noted after both the 220 grit tumble and 320 grit tumble that further wearing away of the stone did not do away with these pits. They would prevent the stone from achieving a smooth polish over all its surface. Further tumbling in 320 grit would not have solved this problem. I have previously (and since) tumbled the same type of stone where the gaseous pockets appear to have been filled in with material and they have been very successfully polished over all their surface.
Stone 1 has polished well except for the many gaseous pits to be found across its surface. Close inspection with my magnifying glass also revealed some small cracks that had not been worn away and which I had not previously noticed:
Stone 1 polished
Stone 1 polished
Stone 1 is covered in small pits that have not polished.
Small pits on the surface of Stone 1
In the centre of this photo, a small crack is apparent
This stone is in contrast to other rhyolites [ignimbrites] I have tumbled, where the gaseous pits have not been void:
Stone 1 is well-patterned and a nice large size. Even though it has failed to polish completely, it remains a fine specimen. The tumbling has brought out its pattern clearly.
STONE 2
Stone 2 is similar to Stone 1 in that it is of volcanic origin [probably rhyolite] and also started out with noticeable gaseous pits the size of which was actually a little larger than Stone 1. However, most of these pits were filled with material which resisted crumbling and which polished quite well. In general, Stone 2 polished much better than Stone 1. However, there are a small number of pits which did not polish and two small cracks that are apparent.
Stone 2 after polishing
Stone 2 after polishing
A pit that crumbled and did not polish
Another pit
Two cracks that had not been removed by tumbling
When rubbing a thumb across one side, a couple of these indentations are noticeable and interrupt the smoothness. Another tumble in 220 grit would probably have removed most of the pits and cracks, although there is no guarantee that all of them would have disappeared.
STONE 3
Stone 3 looks like a mudstone that has undergone metamorphic pressure. It is fine-grained and has lovely green patches and swirls. From the beginning it seemed free of pits and cracks and had polished very well. The beautiful patterns discernible in the rough stone have been revealed and clarified.
Stone 3 after polishing
Stone 3 after polishing
Close-up of a polished Stone 3
Close up of a polished Stone 3
There is just a slight roughness along one edge, not very noticeable really, but otherwise it is excellent.
STONE 4
It was noted during the inspection of Stone 4 after the 100 grit tumble that it had a small indentation in it. I would normally have tumbled it again in 100 grit, although there is always the risk that this might reveal other soft spots. After the 320 grit tumble, I saw that the indentation had smoothed out a lot and thought that it might not affect the final polish. At the end of the polishing process, Stone 4 has turned out very well.
The polished Stone 4
Stone 4 after polishing
Detal of Stone 4 after polishing
Partially smoothed out indentation
Area of partially smoothed out indentation
This stone is a breccia, composed of broken angular fragments of rock cemented together in a fine-grained matrix. Sometimes indentations in such stones are caused by a softer fragment being worn away more quickly than the rest of the stone. This is not the case here – the indentation is maybe a less compressed part of the matrix. It has polished to a significant extent but can still be felt when a thumb is rubbed over the surface of the stone. The only other notable thing is that the very edge of the point half way down the stone is slightly rough – another 320 grit tumble would have smoothed this out.
STONE 5
This stone has polished very well. It feels smooth all over. The eye can vaguely discern a few very small pits along one side which can be confirmed with a 3x magnifying glass. But these do not detract from the overall smoothness.
Stone 5 after polishing
Stone 5 after polishing
Close-up detail of Stone 5
Stone 5 looks at first glance to be a metamorphic mudstone or sandstone but closer inspection shows it to include lots of small pieces of different things, including pits (filled in) that are normally found in a volcanic stone. Many of the stones I find cannot easily be identified by me.
I mentioned towards the end of a previous post that I had met Maike and Martin, a young couple from Germany, on Gemstone Beach in March. I agreed to tumble-polish some stones for them. Today I finished the process, and Petra my wife will take the stones to Germany when she travels there in a couple of days.
Altogether, Maike and Martin collected 83 stones on Gemstone Beach. The largest is 6 cms by 3 cms, the smallest being about half the size of my small finger-nail. All 83 fitted nicely into a 3lb tumbling barrel. I am very impressed with the resulting product, an excellent set of polished Gemstone Beach “gems”! Maike and Martin collected well.
The following are photos of the original stones, dry, then how they looked after their first tumble in 320 grit, and then how they looked after their final polish:
The 83 stones as found on the beach.
After the first tumble in 320 grit.
After the final polish.
Firstly, the stones were tumbled in 320 grade silicon carbide for seven days, then tumbled in Sunlight soap for six hours. Secondly, they were in a five-micron tin oxide “pre-polish” tumble for five days, then tumbled in Sunlight soap for 16 hours. Thirdly, a one-micron tin-oxide “pro-polish” stage took eight days, followed by 27 hours in borax soap. The whole process took 22 days. This is probably the shortest time I have ever polished stones, but the outcome was very good. Initially the stones weighed 780 grams, finishing up at 689 grams, thus losing 10% of their mass, most of it in the 320 tumble stage.
The following photographs provide comparisons of some of the polished stones with how they looked initially, when found on Gemstone Beach. To start off with, here are three of the larger ones:
Maybe a kind of argillite, a mudstone.
Banded rhyolite stone.
Further comparisons for larger stones:
As found on the beach.
Polished.
Different textures.
As found on the beach.
As found on the beach.
Polished.
Some of the medium-sized stones:
Two polished stones.
Before polishing.
Before polishing.
Before polishing.
Polished.
As found on the beach.
Polished.
Smaller stones:
White quartz stones as they were on the beach – practically polished already!
Some other small stones from the beach.
Some small green stones from the beach.
The polished stones.
One of the stones is a small jasper button:
Before polishing.
The polished jasper stone is at the right.
Finally, some of the smallest stones collected by Maike and Martin:
Before polishing.
After polishing.
When packaging the stones to send to Germany, to complete Maike and Martin’s set of outstanding Gemstone Beach stones, I added a hydrogrossular garnet and a stone with a fossil worm cast. These are iconic Gemstone Beach gems, with the hydrogrossular garnet especially sought after, and the fossil worm cast being reasonably distinctive to this coast. As they were absent from Maike and Martin’s haul, I took the liberty of adding them to the package heading overseas.
White hydrogrossular garnet (left) and what is probably an argillite stone with a fossil worm cast (right).
Part One of this Series, about 12 stones, can be found here. The four Posts in the Series each describe the characteristics and origins of three different stones. This Post describes Stones #10 (from Riverton), #11 (from Birdlings Flat) and #12 (from Hokitika).
10) Stone #10 Whitish Quartzite stone with Clear Silica Inclusions, found at Riverton.
I have explained the origins and characteristics of Quartzite in relation to Stone #7 and have provided photos of Quartzites from Birdlings Flat in relation to Stone #8, both in Post Three. Quartzite stones can be found in a number of locations in the South Island. They can have a wide range of colours. One of their frequent characteristics is the clear inclusions of silica running through the stone. Quartzites polish outstandingly, due to their hardness and colours.
For the location of Riverton, see the end of the section on Stone #2 in Part One.
11) Stone #11 Banded Agate, found at Birdlings Flat.
Malcolm Luxton is a collector of Agates. He lives in Ashburton, close to New Zealand’s greatest agate-bearing locality of mid-Canterbury. In his excellent book, “Agates of New Zealand” (2015), he provides hundreds of photos of cross-sections of Agate rocks and stones he has collected from throughout New Zealand.
Cover of Malcolm Luxton (2015) “Agates of New Zealand”, Agate Orphanage Press, Ashburton.
Moss agate, Woolshed Creek, Canterbury – Page 33 of Luxton’s (2015) “Agates of New Zealand”
Banded agate, Stew Point Station, Canterbury – Page 91 of Luxton’s (2015) “Agates of New Zealand”
Banded agate, Rakaia Gorge, Canterbury – Page 230 of Luxton’s (2015) “Agates of New Zealand”
Agate in dark rhyolite, Woolshed Creek, Canterbury – Page 192 of Luxton’s (2015) “Agates of New Zealand”
Coloured Canterbury beach agate – Page 254 of Luxton’s (2015) “Agates of New Zealand”
Luxton offers this explanation for the origin of Agate:
An agate…is a stone that formed as a secondary filling in the various shaped cavities generated or forged within…lava flows. Initially these cavities were created by trapped gases or liquids or by geological processes that produced cracks or ruptures. The secondary filling permeated the lava as a silica-rich solution, and…solidified inside these cavities, thus replicating the shape of its magmatic womb. If additional materials were present, either in the silica-rich solution or growing in the cavity prior to its introduction or introduced as by-products from the surrounding lava, those minerals may have been responsible for structures, assemblages and colours (page 16).
Luxton notes that much Agate material is discharged by Canterbury rivers into the sea and some of it is cast back onto more than 100 kms of Canterbury beaches. The movement of Agates by northerly coastal currents “accounts for the notoriety of Birdlings Flat as an agate-collecting destination” (Luxton, 2015, page 250). He then refers to Vince Burke’s collection in the Birdlings Flat Gemstone and Fossil Museum.
Wall display of rocks and their origins, including Agates,Birdlings Flat Gemstone and Fossil Museum
Agate shelf display, Birdlings Flat Gemstone and Fossil Museum
Coloured Agate cross-sections, Birdlings Flat Gemstone and Fossil Museum
Large Agate rock, Birdlings Flat Gemstone and Fossil Museum
Birdlings Flat Gemstone and Fossil Museum
Birdlings Flat Gemstone and Fossil Museum
Birdlings Flat Gemstone and Fossil Museum
Upon my visits to Birdlings Flat, I have collected a few Agates, mainly quite small ones, though my wife Petra is much better at spotting them than I am! Some of the Agates I have found are just plain cloudy silica, some are banded to some extent, some have a little colouring.
Some of the Agates I have collected at Birdlings Flat
Most of the Agates collected are small, with only the occasional larger one
A “blue” Agate stone
A nice moss Agate stone from Birdlings Flat
The only Agate with bright colour that I have found
Some Agates have a whitish tinge on the outside
Banded Agate
Nice little banded Agate from Birdlings Flat
For the location of Birdlings Flat, see the end of the section on Stone #8 in Part Three.
12) Stone #12 White Quartz, found at Hokitika.
Quartz is originally a clear crystal. When subject to heat and pressure, and when water is introduced into it, it becomes white in colour, the colour of the common white “Quartz” stone found plentifully on beaches in New Zealand. However, strictly speaking, this is “Quartzite” rather than “Quartz”, though the latter term is the most common for this white stone. For that reason, and in order to distinguish it from Stones #8 and #10, I will call it “Quartz”.
Southland Museum display on Quartz. Top centre is a clear piece of Quartz
The clear Quartz in the Museum display
When walking beaches, it is the bright white Quartz stones that seem to claim the first attention of the collector’s eye. I have collected and polished many white Quartz stones from the beaches of Southland, Canterbury and the West Coast. And it is the West Coast where perhaps the best examples can be found, perhaps due to the closeness to the Quartz source, in the Southern Alps.
Dinner plate full of polished white Quartz stones
Part of a batch of Hokitika stones in the process of being polished
Held up to the light, some white Quartz stones are semi-translucent
Stone #12 was found on the beach just on the south side of the Hokitika River, less than five kms from Hokitika town. I visited there on a dull, cold, rainy day in June 2016. The beach was quite sandy but receding waves revealed drifts of stones. There were signs of coastal erosion, with flax plants being undermined and uprooted, and the end of the gravel road had been washed away.
Hokitika on the West Coast of the South Island
Signs of coastal erosion near Hokitika. June 2016.
Driftwood on the beach.
Stones being revealed by the receding waves.
Drifts of stones on the beach near Hokitika.
Mouth of the Hokitika River, looking north at Hokitika on the far shore.
A large white Quartz stone found at Rapahoe Beach, just north of Greymouth, on the same trip. I had to leave this there as I was travelling home by plane and taking other stones with me.
What Hokitika is most famous for – its greenstone carvers.
Location of Hokitika (click on image below, left), and location of beach near Hokitika where Stone #12 was collected (below, right) (source: Google Maps):
This brings us to the end of this series of Posts.
This Post describes Stones #7 to #9 of the 12 (Part One dealt with Stones #1 to #3 and Part Two with Stones #4 to #6):
7) Stone #7 Red-Stained Quartzite, found near Budleigh Salterton, England.
On two recent visits to England, in 2017 and 2018, I went to a coastal village of about 5,000 inhabitants called Budleigh Salterton in Devon, not far from Exeter. The Doomsday Book records that salt panning was of great importance here, and it may have been as far back as Roman or even Iron Age times, hence the origin of the name “Salterton”. The beach, three miles (nearly five kilometres) in length, has a distinctive mix of stones, many deriving from the Budleigh Salterton Pebble Bed which outcrops in the cliffs there.
Looking south-west towards the village of Budleigh Salterton
Looking north-east along the beach at Budleigh Salterton
Budleigh Salterton beach huts
Beach huts and red cliffs at Budleigh Salterton
The layers of pebbles found in the cliffs at Budleigh Salterton originated over 400 million years ago when sandstones formed under desert conditions in the place in France we now call Brittany. During the Triassic period, these rocks were eroded and transported by vast rivers across what later became the English Channel to form the Budleigh Salterton Pebble Beds. The pebbles then fell onto the beach and have been transported eastwards by the sea, well beyond Budleigh Salterton.
The East Devon and Dorset Coast, known as the Jurassic Coast, has become a World Heritage Site due to the geology of the area. In 95 miles (150 kms), 185 million years of earth history are on display in the coastal cliffs. Older Triassic rocks (between 251 million and 200 million years old) give way to Jurassic rocks (200 million to 145 million years old) and younger Cretaceous rocks (145 million to 66 million years old).
Part of an Information Panel in Budleigh Salterton
Information Panel section on the pebble beds
Red pebble cliffs
Dry stones on Budleigh Salterton beach
When the stones are wet, their colours become apparent. In the middle is a stone with dark red speckles, just like Stone #7
Stone #7 is at bottom centre, just off the beach
The British geologist Ian West has a very interesting web page on Budleigh Salterton and the surrounding area (even though it can be difficult to read in places). There he states that the dominant pebbles in the Budleigh Salterton Pebble Bed are quartzite (if you go to this link, click again on it to enlarge the writing at the bottom of the photo). Quartzite is a very hard durablemetamorphic rock composed almost entirely of quartz. It forms when a quartz-rich sandstone is altered by the heat, pressure, and chemical activity of metamorphism. These conditions recrystallize the sand grains and the silica cement that binds them together. The result is a network of interlocking quartz grains of incredible strength. Impurities in Quartzite can cause it to be yellow, orange, brown, green, or blue. The presence of iron results in pink, purple or (as with Stone #7) red.
Location of Budleigh Salterton in south-west England (source: Google Maps):
8) Stone #8 White-Grey Quartzite.
I collected this stone at Birdlings Flat, Canterbury, a beach that I try to visit at least a couple of times each year because of the Quartzites, Jaspers and Agates (see Stone #11) to be found there. Birdlings Flat is the beach immediately south of Banks Peninsula, part of Kaitorete Spit, an enormous barrier gravel bank which lies between Lake Ellesmere and the sea. Stones washed down from the Alps by Canterbury rivers are swept northwards along the coast and deposited here.
Where Birdlings Flat beach meets with Banks Peninsula
Looking southwest along Birdlings Flat beach
The waves are powerful and unpredictable, especially at the Banks Peninsula end
The Birdlings Flat beach is part of the 25 km long Kaitorete Spit which consists entirely of stones
Looking for stones about eight kilometres along Kaitorete Spit
As mentioned in relation to Stone #7, Quartzite is a very hard durable metamorphic rock composed almost entirely of quartz. Many different coloured Quartzite stones can be found at Birdlings Flat, as attested by the collection to be found at the Birdlings Flat Gemstone and Fossil Museum, which I have visited a number of times.
Part of the Quartzite Collection at the Birdlings Flat Gemstone and Fossil Museum. At top right is a large white-grey stone, with a fault through it. Photos with permission
Some white-grey Quartzite stones similar to Stone #8 can be seen on the lower row
Another part of the Quartzite Collection at the Birdlings Flat Gemstone and Fossil Museum
More Quartzite stones, Birdlings Flat Gemstone and Fossil Museum
Stones in Birdlings Flat Gemstone and Fossil Museum, including Quartzites
Stone #8 is one of a number of white-grey Quartzites I have found at Birdlings Flat. The large bands of white and grey provide a striking contrast, making this stone particularly attractive.
Stones collected at Birdlings Flat, including some white-grey Quartzites
Two Quartzites from Birdlings Flat
Two good-sized tumble-polished Quartzites from Birdlings Flat
A darker white-grey Quartzite
Quartzite with more white than grey
A white-grey Quartzite found and polished by Petra
I picked up this interesting little stone at Henderson Bay, Riverton Rocks. I initially wondered if it might be a piece of petrified wood, given its pattern and texture. Some agatised wood (see photos below) that I have seen has some similar patterns. Petrified wood forms when wood is buried by sediment and protected from decay by oxygen and organisms. Groundwater rich in dissolved solids flows through the sediment, replacing the original wood material with, for example, silica, calcite, or pyrite. Agatised wood has been petrified by agate, a form of chalcedony or microcrystalline quartz. However, the agatised wood I have seen tends to be quite glassy when polished, something absent from this stone.
Agatised wood specimens at the Birdlings Flat Gemstone and Fossil Museum
Petrified wood bought at Hettie’s, Akaroa, March 2017
Hettie’s Rock and Crystal Shop, Akaroa
Another side of the same piece of petrified wood
I have also seen petrified wood at Curio Bay, about 130 kms east of Riverton.
Curio Bay, Catlins Coast, Southland
Information Plaque about Curio Bay
The steps down to Curio Bay
Looking down on Curio Bay from the top of the steps
Trunk of a petrified tree at Curio bay
Petrified wood in the rocks at Curio Bay
Petrified wood in the rocks at Curio Bay. My foot for scale
Petrified wood in the rocks at Curio Bay
On the basis of what I have seen, I am unsure whether Stone #9 is agatised wood or some other form of petrified wood, or something entirely different. I have more unidentified stones than identified ones in my collection. [Later I came to the view that this stone is much more likely to be a mix of quartz and a black mineral, not any type of petrified wood.]
I found Stone #9 at Henderson Bay, the last of the Bays that make up Riverton Rocks, the part of Riverton that is made up of holiday homes. My grandparents owned a “crib” (“bach” to North Islanders of New Zealand) at Henderson Bay, up on the hill overlooking the sea, and when I was a boy my family spent two weeks every summer on holiday there.
Henderson Bay, Riverton Rocks, September 2018 – the road continues on to the Back Beach
Henderson Bay, February 2016
Henderson Bay, looking back at the steps
Argillite rocks at Henderson Bay, stones above the high tide mark on the beach
Drift of stones, Henderson Bay
Henderson Bay stones
Henderson Bay stones
Location of Henderson Bay and Back Beach, Riverton (source: Google Maps):
Part Four is the final Post in this series, dealing with Stones #10, #11 and #12.
