A Review of the “Geological Digressions” Website

This Review originally appeared in the June 2026 edition of “StoneSpeak”, the Newsletter of the Southland Geological and Lapidary Club. Below is a slightly expanded version. An Index to this Series of Reviews is here. The Southland Club’s website is here and its Facebook Page is here.

When I was looking for good introductory material about trace fossils three years ago, I came across an excellent article “Someone passed this way: Tracks, trails, impressions, and footprints” on the “Geological Digressions” website. I liked the turn of phrase used there: “Trace fossils are what is left of the activity of some ancient critter”. It turned out that the site is produced by a retired New Zealand geologist, Brian Ricketts.  

Home Page of “Geological Digressions” http://www.geological-digressions.com.
Trace Fossils article on “Geological Digressions” http://www.geological-digressions.com/someone-passed-this-way-tracks-trails-impressions-and-footprints
From Trace Fossils article on “Geological Digressions” http://www.geological-digressions.com/someone-passed-this-way-tracks-trails-impressions-and-footprints

Ricketts first studied geology at the University of Auckland in the early 1970s and did his doctoral degree in the Canadian Arctic. He then worked for the Geological Survey of Canada (GSC) for a few years. “I quit the GSC in 1997 and moved with my Canadian family back to Aotearoa–New Zealand to work a 4-year teaching stint at the University of Waikato.” But “with an evolving disenchantment of academia, I decided to form my own consulting company in 2005 – a company of one – and never looked back!” (quotes taken from “A Geological Life” on the website). During his time as a geologist, he also worked in Hungary, Chile, Australia, USA, the United Kingdom and the Netherlands. Retired now, Ricketts spends time on his Waikato organic kiwifruit orchard but also continues the development of “Geological Digressions”. More details on his background can be found in “A Geological Life”.

Ricketts started his website in December 2015. He states there that “I do this for the love of it. I do not receive any remuneration for the site (and I don’t advertise). The website is not attached or beholden to any organization.” The main part of the site is a “Virtual Classroom” containing material on sedimentology, stratigraphy, volcanology, geological structure, sedimentary basins, petrography and petrology – this is aimed primarily at university undergraduate students. There is a lot of material here – 23 Main Sections, each with numerous articles – and often useful links are made to other sources as well as related pages in “Geological Digressions”.  

“Virtual Classroom” Page http://www.geological-digressions.com/how-to-do-field-tasks.
“Bivalve morphology for sedimentologists” http://www.geological-digressions.com/bivalve-morphology-for-sedimentologists
“Ripple Lithofacies – Ubiquitous Bedforms” http://www.geological-digressions.com/ripple-lithofacies-ubiquitous-bedforms.

For example, in the Virtual Classroom Main Section “Minerology of Sandstones”, there are 20 articles, one of which is on “Bivalve morphology for sedimentologists”. It looks at bivalve fossils in detail, including their external and internal morphology, and shell orientation, with well-labelled illustrations. One of the other Main Sections is “Lithofacies”. Lithofacies refers to the physical and compositional characteristics of a sedimentary rock unit or sediment layer. There are 41 articles in the Section, one of them being “Ripple Lithofacies – Ubiquitous Bedforms”. It describes how ripples are formed on sedimentary surfaces and their different characteristics.   

This “Virtual Classroom” is an excellent resource for people who have not formally studied geology – here you can get access to some of the material that is presented to university students. Yes, it can be technical, but it is well presented and a treasure for the keen learner.

Other articles in “Geological Digressions” are written with non-specialist or non-technical people in mind. Across the top of the site’s pages are links to four groups of articles: Glossary, Atlas of Sediments, Ancient Earth, and More. There are 11 glossaries (alphabetical lists of technical terms with their meanings), on topics including Stratigraphy, Sedimentary Structures, Volcanics, and Palaeontology. Alongside the explanations of key terms are links to any website articles relevant to them. “Atlas of Sediments” is a collection of photos that Ricketts has accumulated. There are 24 groupings here. One of them, for example, is “Atlas of Trace Fossils” which has 33 photos of different trace fossils, some from New Zealand.

One of the Glossaries http://www.geological-digressions.com/glossary-paleontology.
“Ancient earth. 2 How old is it?” http://www.geological-digressions.com/ancient-earth-how-old-is-it.
Sandstone formation http://www.geological-digressions.com/from-sand-to-stone-sandstone-a-remarkable-transformation.

The “Ancient Earth” heading takes you to 13 articles. The second one asks how old the Earth is. Here, Ricketts looks at a number of people in history who have attempted answers. He then refers to the search for the oldest rocks on Earth and what they imply. Another “Ancient Earth” article is on stromatolites, the earliest physical life form on Earth. Under the “More” heading are 14 other topics, some of which contain a lot of different articles. For example, “Interpreting Earth” has 28 articles, ranging from how sand gets turned into stone to understanding how a fossil forest in the Arctic has survived.

As you can see, “Geological Digressions” is large, detailed, diverse and wide-ranging, containing both technical and non-technical geology-related information broadly defined. The Home Page refers to “436 articles” being there. In general, these are well-written and have lots of interesting detail and illustrations. You can use the “Search” function to look for something specific. Or you can take a stroll along its many corridors, exploring whatever takes your fancy.

The next Review in this Series is of the “Geology.com” website. The Series Index is here. 

Fifty Polished Kai Iwi Beach Stones for the Book Man: Part Two, Stones 11 to 20

I gifted 50 polished stones found on Kai Iwi Beach, near Whanganui, to Cam who sold me some books at a good price. Many of the stones I gave to Cam are some variety of quartz, the predominant type of stone on Kai Iwi Beach. Part One describes the background and the first ten stones.  This Post describes another ten of these stones.

Stone 11  again consists primarily of quartz, with only a light sprinking of iron oxide in it. You can’t see many quartz crystals in it due to their tiny size and tight compaction:

Stone 11.
Other side of Stone 11.

By contrast, Stone 12, another quartz, has hardly any iron oxide in it and some small clear quartz crystals are much more obvious in it:

Stone 12.
Other side of Stone 12.

In Stone 13, the iron oxide is laid down across only part of the stone so that where it is absent appears as white bands of varying width:    

Stone 13.
Other side of Stone 13.

Stone 14 is what I call a “two-sider” – the two sides differ enough from each other that you could be forgiven for thinking they might belong to two different stones. The main difference is the absence or presence of yellow:   

Stone 14.
Other side of Stone 14.

I am not sure what type of stone is Stone 15. It’s not the usual iron oxide-stained quartz. It contains a mineral that gives it a green hue, and the rectangular-like crystals in it are probably not quartz but are more likely plagioclase feldspar, another very common rock-forming mineral:

Stone 15.
Other side of Stone 15.

Stone 16 is a small dark red jasper. Jasper is a type of chalcedony or microcrystalline quartz, a dense aggregate of microscopic quartz crystals too small to be seen with the naked eye. It is opaque due to the presence of minerals which give it colour, with the red of iron oxide being most common. Jasper is usually classified as sedimentary, precipitating from solutions moving through the ground.   

Stone 16, jasper.
Other side of Stone 16.

The stone could be called a “brecciated” jasper, having been fragmented to some extent by tectonic stress. The small areas between the fragments have become veins as they have been filled by mineral. The larger veins contain some white quartz, stained yellow/orange. The many fine veins in the stone have been filled with a clear mineral which could, again, be quartz. “Brecciation” has previously been explained in relation to Stone 2 (see Part One).

Stone 17 is a white quartz – you can see tiny clear crystals in the close-up photos which are embedded in a “frothy” white quartz mix, likely to contain water and/or air: 

Stone 17, quartz.
Other side of Stone 17.

It is similar to Stone 12 (above, earlier in this Post) but the shape and distribution of the tiny clear crystals is a bit different.   

Stone 18 has some similarities to Stones 4 and 9 (see Part One), consisting of white, yellow, brown and black crystals:

Stone 18.
Other side of Stone 18.

The white is quartz, the yellow and brown is iron oxide, and the black (sometimes sparkly) will be mica.

 Stone 19 has an unusual black patterning on it, one that caught my eye on the beach:    

Stone 19.
Other side of Stone 19.

Again the stone is quartz with some yellow/orange iron oxide, but I am unsure what the black mineral is.

Stone 20 is completely black:

Stone 20.
Other side of Stone 20.

There are a few tiny light areas on each side of the stone, hinting that it is quartz that has been flooded by a black mineral. I used photo software (Picasa 3) to lighten the close-up images to reveal some of the subtle patterns on the stone’s surface – on the left are the original images, on the right are the lightened ones:

Part Three, Stones 21 to 30, is not yet available.  

Fifty Polished Kai Iwi Beach Stones for the Book Man: Part One, Stones 1 to 10

Recently I was wanting to buy some books on Scottish Island knitting patterns on behalf of my wife. I inquired at my favourite local secondhand bookshop, Book Hunters on Ridgway Street in Whanganui. There I spoke to Cam who said they had none in stock but he would look out for them, and he wrote my contact details in his book. Not long afterwards, he rang to say he had found a bunch. They were just what I was after, and he gave me a good deal on them. I knew he lived at Kai Iwi Beach so I asked whether he would be interested in a gift of some tumble polished stones from there. He said yes, so I have picked out 50 to give to him. 

Kai Iwi Beach is my local beach and from time to time I walk Jasper the dog there. There are not many stones on that beach – in fact, the area is much better known for fossils, especially of moa. The nearby village is called Mowhanau and it is thought the name could have originally derived from “moa-whanau”. I automatically look for stones when I am on any beach. As a result, over the past few years I have collected quite a few from Kai Iwi Beach that I have gone on to tumble polish. Most of them are quartz that have been stained yellow-orange by iron oxide – see “The Iron-Stained Stones of Kai Iwi Beach”. A few other stone types occur, and I recently found a trace fossil in argillite and an orbicular jasper, both rare. With even ordinary appearing stones, however, when they are viewed up close, there is quite a variety of interesting colours and patterns in them.   

Jasper on Kai Iwi Beach.
Second hand books from Book Hunters.
Fifty polished Kai Iwi Beach stones.
Some of the stones.

 The 50 stones given to Cam are presented in this series of Posts in no particular order. The first ten are below.

 Stone 1 could be mistaken for a jasper, given its red hues. However, it is more likely to be quartz with its colour due to the presence of iron oxide:     

Stone 1, a type of iron oxide-stained quartz?
Other side of Stone 1.

Quartz is one of the most common minerals on Earth and is hard and glassy. Its purest form is rock crystal which is colourless and transparent. However, more often quartz stones incorporate other minerals which give them colour and make them opaque. Iron oxides include a number of chemical compounds such as hematite and limonite. They can colour stones a number of hues, from yellow to orange to red to brown and even black.

Stone 2 could be a mudstone because of its very fine grained and smooth character. Mudstone is a sedimentary rock, often laid down on the ocean bed. But what is most interesting about Stone 2 is that it has fragmented in places due to tectonic stress. Great weight of rock can move slightly and deform or break-up what lies beneath. The fragments in Stone 2 are angular which means the stone could be viewed as a kind of breccia – see “T is for a Type of Tiny Tectonic Breccia?”   

Stone 2, brecciated mudstone?
Other side of Stone 2.

Stone 3 is more typical than Stone 1 for the kind of iron oxide-stained quartz from Kai Iwi Beach, being more orange-yellow in colour. It is more spherical in shape than most of the stones on the beach which tend to have two distinct flat sides:    

Stone 3, typical Kai Iwi Beach iron-stained quartz.
Other side of Stone 3.

Stone 4 is made up of lots of tiny bits of quartz and other minerals. It could be a kind of sandstone, formed from the compaction of these tiny bits, though most sandstones have finer grains:     

Stone 4.
Other side of Stone 4.

Stone 5 is another iron oxide-stained quartz but the mineral is distributed within the stone quite differently from Stone 3, with the quartz itself sometimes showing white around the edges: 

Stone 5.
Other side of Stone 5.

Stone 6 appears in some ways to be a more compact version of Stone 4, made up of lots of tiny bits of quartz with iron oxide providing a yellow-orange colour: 

Stone 6.
Other side of Stone 6.

Stone 7 is again likely to be made up primarily of quartz but there is a black mineral in it providing a different character to the previous stones:

Stone 7.
Other side of Stone 7.

Some stones look different on different sides. Stone 8 is an example of this. Again, it is an iron oxide-stained quartz, similar in many ways to Stone 5, but the distribution and pattern of the colour-providing mineral varies a lot on the two different sides:    

Stone 8.
Other side of Stone 8.

Stone 9 has some similarities to Stone 4 but has more small dark mineral bits in amongst the tiny quartz crystals. I suspect some of the dark bits are biotite mica, which also sparkle when they catch the light just right:    

Stone 10, the final one in this Post, is again an iron oxide-stained quartz. Some areas of the stone have no colour-providing mineral in it and it seems as though you can see into the quartz to some extent:  

Stone 10.
Other side of Stone 10.

Stones 11 to 20 are described in Part Two.  

Tumbling an Orbicular Jasper Found on Kai Iwi Beach, Whanganui

Currently I am spending most of my time working on a photo book on Gemstone Beach stones. At this stage, I have collected together photos from the last four years and drafted text for entries on 20 diffferent stone types. I am just finishing writing six sections for the Introduction. I next need to edit some of the text I write earlier, to improve it. Chrissy is working on the layout, and we will eventually need to get together to finalise things.

But I am also finding the opportunity to tumble some stones, including this Kai Iwi Beach one. I found it about ten weeks ago and think it is probably an orbicular jasper – see this Post. I have recently tumbled it in 400 grit for 11 days and then in 600 grit for 10 days. It has come out nice and smooth, ready to go to a final polish stage. When found, the orbs in the stone were raised, suggesting they are harder than the rest of the material. I wasn’t sure if tumbling might not produce a completely smooth surface, but it has. Following are photos of the stone as found (below, left) followed by the stone after tumbling to date (on the right):

Stone when found.
Stone after 400 and 600 grit tumble.
Stone when found.
Stone after 400 and 600 grit tumble.
Stone when found.
Stone after 400 and 600 grit tumble.

The orbs have an interesting structure and are nicely defined. I am pleased with progress so far and look forward to seeing what it looks like when polished. 

A Review of Three Kiwi YouTube Rockhounds

This Review originally appeared in the April-May 2026 edition of “StoneSpeak”, the Newsletter of the Southland Geological and Lapidary Club. Below is a slightly expanded version. An Index to this Series of Reviews is here. The Southland Club’s website is here and its Facebook Page is here.

Anyone can used their phone camera to take photos and make video clips of their activities and post them on social media. Facebook, Instagram and YouTube are popular outlets and some rockhounds have not been reluctant to use them. They provide a great way to store images of a find or a fossick that you can go back to anytime to enjoy. And other people can enjoy and learn from them too. Here is a review of how three New Zealanders have used YouTube to store and share their videos of stones and fossils.

Nicola Gray, who lives in Hastings, Hawkes Bay, has a Facebook Page and YouTube channel, and she is active on a number of Facebook Rockhound Groups. Her YouTube channel “New Zealand Rockhound” documents many of the details of her fossicking and tumble-polishing, as well as stone cutting and craftwork. Introducing herself on YouTube, Nicola states: “I love rock hunting, and especially love sharing my finds with others. I really enjoy sharing my rock tumbler barrel washouts. I make beautiful pendants from my stones too.” For Nicola, making and editing and posting videos are a regular and natural part of being a rockhound.

Nicola Gray’s YouTube Channel http://www.youtube.com/channel/UCSQMZ5-H0nsBL_bM2BjNEHw/videos.
Nicola Gray’s videos.
More of Nicola Gray’s videos.

I first met Nicola when she travelled south with Angie Nicholas to visit Gemstone Beach in April 2023. At the time I was nearing the end of my “Southern Sojourn” on the south coast. Our first joint fossick there is described by me in this Post and this Post, with two further fossicks described here and here. Nicola’s own video of visiting Gemstone Beach can be found here – it is just over eight minutes long and has been viewed over 3,100 times.

At the time I wrote this Review, in early April 2026, Nicola’s channel contained 479 videos and had 1,130 subscribers. I went through her latest 50 videos to identify their content. I found that in 12 of them, Nicola was showing different types of stones, sometimes recently arrived in the mail from other people, sometimes recently tumbled/cut or about to be tumbled/cut. Another 12 of her latest 50 videos showed Nicola washing out a tumble barrel or vibratory tumbler. Nine showed her cutting stones, and eight recorded her looking for stones on a beach somewhere in New Zealand (such as in Hawkes Bay, on the south coast including Gemstone Beach, and the West Coast). The other nine videos were on topics such as loading a tumbler barrel, tumbling advice, and a microscopic view of a stone.

At the top of the list of videos on a YouTube channel, you can click on “Latest”, “Popular” and “Oldest” to help you move among them in different ways. Nicola’s most popular video, viewed 30,878 times, is a short 33 second clip posted in October 2020 recording her discovery of a storm jasper in the Tukituki River. Most of Nicola’s videos are between about three minutes and 12 minutes in length with only the odd one lasting more than 20 minutes. So, in many ways, they are snapshots into the daily life of a rockhound who cuts and polishes her finds.

Gordon Sherwood and his wife Beth have a crystal and wellness shop in Edgecumbe, Bay of Plenty, called Heaven’s Ascent. Gordon has a Facebook Page under the title of “New Zealand Rocks Downunder” which is also the name for his series of YouTube videos. He introduces himself as follows: “I live in the Eastern Bay of Plenty, and have to travel to other areas for older rocks that contain interesting specimens.  You can expect to accompany me as I find interesting rocks, fossils, and uncover some of the interesting insect life here in New Zealand. Look out for my attempts at cutting and carving the rocks that I have found as I get the gear together to do it… Our retail shop has a great selection of crystals and gemstones that fuels this passion to fossick, which is squeezed in whenever I can, going AWOL without getting in too much trouble with the Mrs.” In July 2025, Gordon and Beth featured in an Eastern Bay article celebrating National Tartan Day.

Gordon Sherwoods YouTube Channel http://www.youtube.com/@NewZealandRocksDownunder/videos.
Gordon Sherwood’s videos.
Source: https://easternbayapp.co.nz/news/articles/6865b5eb80a872f72cee39b5

Gordon has had some health issues which sometimes delays new postings. However, at the time I wrote this Review, his YouTube channel contained 138 videos and had 2,030 subscribers. His most popular video, “Uncovering the Secrets of Gemstone Beach” (33 minutes long), was posted in August 2023 and has been viewed 48,315 times. Gordon’s videos tend to be longer than Nicola’s, usually between 15 and 30 minutes. There is more of a narrative to each piece and they are often quite informative about a stone type or fossicking place. Some topics are: excavating microfossils at Matata Beach (a favourite destination), visiting the Tauranga Gem and Mineral Club 2024 Show, searching for pounamu greenstone at Jackson Bay, looking for pakohe (a traditional stone used for tool making and carving), fossicking at Birdlings Flat, and fossil hunting at Motunau Beach.

The third YouTube user is Morne of “Mamlambo Fossils” whose first video was posted in May 2019. He has become very well-known: Newsweek had an article on “Morne Mamlambo” in June 2021; TV1’s Seven Sharp had a five-minute feature on him, shot on Motunau Beach, in November 2024 , reporting that he had rented a hall at the old Waikuku School in Canterbury as a workshop, fossil museum and educational centre; and on 30 March this year RadioNZ interviewed him in their Monday Afternoon Expert segment.

Morne, who declines to give his surname, is a software engineer and grew up in South Africa. He introduces himself as follows: “I’m an amateur fossil hunter living on the South Island of New Zealand. I enjoy hunting the coastal cliffs for Miocene and Cretaceous era fossils and venturing further afield for the petrified wood and fossils that can be found there. I’m constantly learning about the fossils that can be found here in New Zealand. I also use a variety of tools and techniques to prepare the fossils I find which I then donate to New Zealand museums.” He has taken the name “Mamlambo” from a mythical South African creature which has the head of a horse, the lower body of a fish, short legs, and the neck of a snake. He started off by taking videos of his finds to show his family back in South Africa and attracted quite a bit of attention when he posted them on YouTube.

Morne Mamlambo’s Fossils Channel http://www.youtube.com/@MamlamboFossils/videos.
Morne Mamlambo’s Rocks Channel http://www.youtube.com/@mamlamborocks/videos.
Guided fossil walks offered https://mamlambofossils.com/fossiltours.

Morne has a number of online and social media outlets, including a website, and he posts videos on all of these. One of the things on his website is his offer of paid guided fossil walks. At the time I wrote this Review, his “Mamlambo Fossils” YouTube channel contained 370 videos and had 611,000 subscribers. His videos record his hunts for fossils, the many hours he spends preparing them (using a variety of tools to wear away the surrounding rock), and issues around their identification. One of his most popular videos from 2021 “MONSTER fossil crab prep – the 50lbs crab finally gets prepped… and it’s a beast!” is 13 minutes long, has been viewed 2,443,525 times, and uses speeded-up photography to show the 208 hours of work he spent revealing the fossil. He has made lots of fossil finds, many of them very significant, such as a new species of billfish, now officially named Zealandorhynchus fordycei, honouring the late Ewan Fordyce, an influential University of Otago vertebrate palaeontologist.

Morne also has a second but smaller YouTube channel called “Mamlambo Rocks”. It contains 50 videos and has just over 10,000 subscribers. The most popular of these videos are on agate hunting in Canterbury. There is also a 48 minute video of most of an August 2025 talk on agates by the late Malcolm Luxton. Other videos feature petrified wood and fossicking in such places as Birdlings Flat and the Conway River.

It takes time to view a video online – you can’t just glance at it like you can a still photograph. And you don’t know how interesting or useful it will be until you’ve seen it through. But a good video can take you right into a promising rockhunting area, and show you what to look for, much more effectively than just written text. Watching a couple of their homemade videos allows you to assess if the approach of a rockhound works well for you, providing enjoyment and learning and inspiration.

“Thank you!” to these three rockhounds for sharing their passion and knowledge with us.

The next Review in this Series is of the New Zealand-based “Geological Digressions” website. The Series Index is here. 

A Review of “AlexStrekeisen” Website

This Review originally appeared in the March 2026 edition of “StoneSpeak”, the Newsletter of the Southland Geological and Lapidary Club. Below is a slightly expanded version. An Index to this Series of Reviews is here. The Southland Club’s website is here and its Facebook Page is here.

When I’m doing some research on a rock or a mineral, I usually look at the relevant entry in the “AlexStrekeisen” website. Some of the information there is quite detailed and often accompanied by good photos of rocks.

Cover of “StoneSpeak” March 2026.
Page 7 of “StoneSpeak” March 2026.
Home page of http://www.alexstrekeisen.it/english/index.php
Alessandro Da Mommio. Source: http://www.alexstrekeisen.it/english/index.php

There are also microphotos of thin rock sections at the end of each entry – photos of what you’d see looking through a microscope. These are intriguing and can be quite spectacular:

Calcite and zeolite (grey) filling an amygdale. Field of view = 7mm. http://www.alexstrekeisen.it/english/vulc/amygdales.php
Fragments of various nature in a breccia, field of view = 7mm. http://www.alexstrekeisen.it/english/sedi/breccia.php
Olivine crystals in a dunite, field of view = 7mm. http://www.alexstrekeisen.it/english/pluto/dunite.php
Allanite crystals, biotite and microcline feldspar in a granite, field of view = 7mm. http://www.alexstrekeisen.it/english/pluto/allanite.php
Globigerinids Foraminifera in a Mudstone, field of view = 2mm. http://www.alexstrekeisen.it/english/sedi/mudstone.php
Hornblende, plagioclase and quartz in a type of gabbro, field of view = 7mm. http://www.alexstrekeisen.it/english/pluto/quartzgabbro.php

Alessandro Da Mommio is the Italian geologist behind this website (photo at top of Post, far right). He notes on the home page that his passion for optical petrography inspired him to create an online vehicle for “the recognition and identification of mineral phases in thin section”. The website is available in both Italian and English. If you find yourself on the Italian-language version of the site, click on the Union Jack flag just under the header to be taken to the English-language version.

The website is named after Albert Strekeisen (1901-1998), a pioneering Swiss petrologist who has been very influential in rock classification systems. The QAPF (Quartz – Alkali feldspar – Plagioclase – Feldspathoids) diagram for the classification of igneous rocks is known as the “Streckeisen diagram” in his honour (see image of diagram below, far left). Da Mommio is a geology lecturer at the University of Milan and a specialist in microphotography. Last year, with Victoria Pease he published the book “Atlas of Minerals and Igneous and Metamorphic Rocks in Thin-Section”.

“Streckeisen diagram”, the QAPF diagram for classification of igneous rocks. https://commons.wikimedia.org/wiki/File:Streckeisen_Plutonic_Rocks.svg
Rhodonite page. http://www.alexstrekeisen.it/english/meta/rhodonite.php
Rhodonite, Franklin Mine, New Jersey. http://www.alexstrekeisen.it/english/meta/rhodonite.php
Granular rhodonite crystals, field of view = 7mm. http://www.alexstrekeisen.it/english/meta/rhodonite.php

Da Mommio describes his website as follows: It is “designed for students of geology and petrography and geology enthusiasts… Each page consists of two parts, descriptive (an exhaustive explanation of the mineral phase) and visual (high-resolution photographs).” New pages on rocks and minerals are being added regularly – one of the most recent is Rhodonite which has especially colourful thin-section microphotos (see image above, far right).

The website has five main sections – on the four main types of rocks (plutonic, volcanic, metamorphic and sedimentary) and on the Italian magmatic provinces (areas of volcanic rocks). The rock sections have long lists of contents running down the left margins, arranged under a small number of headings. For example, for Metamorphic Rocks, the main headings are Metamorphic minerals, Texture and microstructure, and Metamorphic rocks. For Sedimentary Rocks, the main headings are Sedimentary rocks [main types], Turbidites, Fossils, Sedimentary minerals, Texture, and Rocks. For each entry under those headings, there is usually a description of the mineral, rock or item, often with technical detail.

Page on Metamorphic Rocks. http://www.alexstrekeisen.it/english/meta/index.php
Page on Sedimentary Rocks. http://www.alexstrekeisen.it/english/sedi/index.php
Page on Plutonic Rocks. http://www.alexstrekeisen.it/english/pluto/index.php

However, the entries vary in length and usefulness, some being quite detailed but others being quite short. A few of the entries rely heavily on Mindat.org, but most go beyond that. Unfortunately, the list of references for minerals and rocks seem to be mainly textbooks, not online sources that you can follow up. For that, you then need to go to such websites as Geology.com and Wikipedia.

The next Review in this Series is of three New Zealand YouTube rockhounds. The Series Index is here. 

March 2026 Stone Collecting Trip – Part 17, Low Tide at Ward Beach, Thursday 2 April

I have a booking on a Cook Strait ferry for tomorrow but the ship has been out of action for a couple of weeks. It was supposed to have started sailing yesterday but cancelled again. Today it looks like it is due to start up again and, if so, I should be lucky tomorrow. I had managed to book an alternative with another ferry company for Sunday and the Flaxbourne Motel owners at Ward, Ronnie and Ian, have very kindly made allowances for me to stay until then if need be. So today’s trip to Ward Beach may be my last fossick for this trip, or it may not.

I arrived at Ward Beach at 12.30 pm at low tide. It was sunny, 18 degrees, with only a light breeze. More than a dozen camper vans and cars were there. However, during the nearly two hours I was there, no one else was on the beach in front of the carpark or to the south, just over the Flaxbourne River, where I walked.

Looking south from in front of the Ward Beach carpark.
Looking notth from in front of the Ward Beach carpark.
At low tides, these rocks to the south are exposed.
The Flaxbourne River flows as a shallow stream here (top right). The mouth is a great fossicking area.
Looking back towards the carpark and camping area.

It was a typical Ward Beach fossick though I was surprised not to spot more trace fossil limestone pebbles. This Series of Posts features the kind of stones I have found most often on this beach. Here are 15 of my finds from this afternoon.

This first one is my favourite – a small stone but with really interesting features and colours:

Samll but busy colourful find.
Other side of stone.

Occasional jaspers can be found on Ward Beach. Many are plain and uninteresting to me, but now and again a fascinating one appears:

This jasper has a bright white vein which may be chalcedony (agate):

Jasper with white vein.

I keep a look out for limestone stones with white veins, and found these three:

This one has dendrites in it (see the second half of this Post for other Ward Beach examples):

Limestone with dendrites.
Other side of stone.

I also look for brecciated limetone (complex veins) and sometimes these might have some flint in them (the clearer brown patches in this case):

Brecciated limestone? Plus some flint?
Other side of stone.

More examples of this can be seen in this Post.

Some limestone along this coast can be yellow and/or blue. This one appears to be brecciated, has a thin black vein and an intriguing white feature:

A dark red stone that I initially thought could be a jasper but I think it is probably some kind of igneous stone – the tiny crystals and patches of mineral in it are interesting:

Igneous stone?
Other side of stone.

Another igneous stone, a type quite common on New Zealand beaches, probably a porphyritic basalt with plagioclase feldspar phenocrysts – the different crystal shapes always fascinate me:

This stone is predominantly light in colour (probably quartz) with black crystals:

Finally, three specimens of trace fossils in limestone:

That night, I met up with Katinka, Guy and their daughter, all keen rockhounds and occasional readers of this blog. They were staying two doors along from me at the motel. On my way to catch the ferry the next day, I stopped off briefly at Ward Beach again and was soon joined by them for about 20 minutes. The tide was not good for finding wet stones however and little eventuated from that fossick. I made it safely home to Whanganui that night.

The Index to this Series can be found here.

Three 2026 Calendars For Sale, Reduced Price

Details about the 2026 TumbleStone Calendar can be found here. I sold the last one in stock a couple of weeks ago, even though it is now well into 2026.

Calendar Cover, 2026.
July.
August.
September.

I have ordered three more copies in case I get another late order or three. The photos themselves can be cut out and put on the wall, if you are so inclined. April’s stones are poppy jaspers, with May’s stones being Kakanui quartzites and April feature black and white igneous stones.

April’s poppy jaspers.
May’s Kakanui quartzites.
The black and white igneous stones of June.

The price these days is 20% off the original price, with postage within New Zealand included, coming now to $28 non-rural, $32 rural. Email john.tumblestone@gmail.com.

March 2026 Stone Collecting Trip – Part 16, An Introduction to St Andrew’s Beach, South Canterbury, Tuesday 31 March

A member of the Facebook Group “New Zealand Lapidary, Rocks, Minerals, Fossils” mentioned to me three weeks ago that the beach near Pareora in South Canterbury was worth a look. Pareora is about seven kilometres south of Timaru South, a beach I often visit. I had a look at the area on Google Maps and decided to drop in on a beach just south of Pareora, a couple of kilometres north of the small town of St Andrew’s. I turned off the main highway onto Galletly’s Road – it’s a very short drive down that road to a freedom camping area right next to the beach. When I arrived at 11.15 am, there were a small number of buses and campervans making use of it, some of them sporting Gypsy Fair signs. A sign warns that an old landfill used to be located at the back of part of the beach. And there are some railway iron posts sticking out of the stones in front of the beach entrance.

Parked at the entrance to St Andrew’s Beach.
Sign at St Andrew’s Beach.

I spent an hour on St Andrew’s Beach. The wind was cool, the temperature about 12 degrees, and it was mainly cloudy. There are a lot of grey stones on the beach. Initially I didn’t spot much else as I walked south along the waves’ edge. I turned back north and shortly thereafter found a small piece of petrified wood. I slowed down and began to look more carefully, soon spotting a few scattered stones worth examination. I ended up spending an hour doing this. As expected, there are a lot of similarities to the stones at Timaru South – some very interesting quartzites and jaspers with the odd unusual stone.

Looking south on St Andrew’s Beach.
Looking north on St Andrew’s Beach.
St Andrew’s Beach stones.
St Andrew’s Beach stones.

Nine of my finds are presented below. The first is the piece of petrified wood I picked up:

Petrified wood from St Andrew’s Beach.
Other side of petrified wood.

This next one is my favourite find, due to its colour and texture – I think it is most likely a quartzite:

Quartzite?
Other side of possible quartzite.

I picked up this small dark stone because I thought I could see spots in it. The close-up photos suggest the “spots” could be spherulites, and maybe the stone is rhyolite – but this is speculation based on my experience with Slope Point spherulitic rhyolite. The photos are not clear enough to confirm my thoughts:

Spherulites?

This small stone has a dark brown mineral through part of it and some brecciation in another area:

Interesting brecciation.
Other side of stone.

Maybe a quartzite, also with some mineral patches and brecciation:

“Top” view.
“bottom” view.
“Side” view.

Some fine mineral lines in this find which look like epidote green:

Fine traces of epidote in this stone?
Other side of stone.

A smaller stone with a little more of the mineral through it:

I think this one could be jasper but I am not sure:

Jasper?
Other side of stone.

Finally, a dark green quartzite of a type that I have found before along the southeastern coast of the South Island:

Quartzite.

Part 17 reports on finds from Ward Beach, the day before I arrived back home in Whanganui. An Index to this Series is here.

March 2026 Stone Collecting Trip – Part 15, Finding Patches of Stones on Seadown Beach, Kakanui, Monday 30 March

I arrived at  Seadown Beach at 3pm, just after high tide. Compared to yesterday, there were fewer stones at the south end of the beach. I decided to walk north to try to find some stone patches and eventually did so, just as I was about to turn around. It was maybe 600 metres from the roadside carpark that four or five large areas of stones appeared. These provided some interesting finds.

Looking south along Seadown Beach.
Looking north along Seadown Beach.
About 500 metres north along the beach, I spotted some stones ahead.
The patches of stones.
The stones were being wet by the waves, assisting fossicking.

It was 19 degrees, partly cloudy, with a light breeze so I didn’t need my hat and scarf. I left the beach two hours after arriving.

I picked up a number of brown stones, looking for those which contain tiny bryozoan fossils. This one turns out to be the most intriguing, looking as if it does have some tiny fossils of some kind:

One side of stone with tiny fossils.
Other side of stone.

This one also seems to have some tiny fossils in it:

Another interesting brown stone.

A small highly brecciated brown stone:

Brecciated brown stone.

A fourth stone I collected because it is brown – it has quite a different texture:

Another interesting brown stone.
Other side of stone.

Four interesting quartzites from this afternoon, all of different character:

Small colourful quartzite,
Yellow hues in quartzite.
Quartzite #3.
Different kind of quartzite, with green vein.

A brecciated white quartz:

Brecciated quartz.

Finally, I think this stone is an agate (chalcedony) but it’s not like any other agates I have found on this beach. It is opaque and contains inclusions that look like the yellow/orange iron oxide that colours many of the quartzites:

One side of agate(?), wet.
The same side dry.
Other side, wet.
Other side, dry.
Opaque when held up to light.

In Part 16, I continue my way north, stopping off at a beach near St Andrew’s in South Canterbury. An Index to this Series is here.