I wrote this Review for the December 2025 edition of “StoneSpeak”, the Newsletter of the Southland Geological and Lapidary Club. The following is a slightly fuller version. The Southland Club’s website is here and its Facebook Page is here.
I was recently doing some research about breccia for a couple of blog posts I was writing (“TumbleStone Calendar 2026: November – Breccia” and “T is for a Type of Tiny Tectonic Breccia?”). By far the best piece I found on breccia was on a website called Sandatlas. The piece is well-written, comprehensive, nicely illustrated, is not shy about being a bit technical but is generally quite readable, and it covers a wide range of relevant issues. It is not a brief piece and it doesn’t oversimplify, but it was invaluable in helping me gain a detailed overview of breccia and its formation. The accompanying photographs and diagrams are outstanding. The rest of Sandatlas is similar.
Sandatlas is the project of Siim Sepp (above, left), an Estonian who describes himself as a software developer, author, geologist, and photographer. He started Sandatlas in 2012 as a website about sand. But what started with photographing sand samples from around the world grew into a broader guide to geology. The website’s home page now states: “Sandatlas is an educational website that aims to explain geological concepts in a clear and accessible way. The content is designed for students, educators, amateur geology enthusiasts, and anyone curious about the Earth’s materials and processes. The site features illustrated articles about rocks, minerals, sand types, and key geological terms – supported by original photographs to help readers better understand the subject matter.”
One of the great things about Sandatlas is Sepp’s high-resolution photos of rocks – he often provides a good range of examples of a rock type, and they tend to be handful size or just a bit bigger, the size you find on a beach or in a river. The majority of the photos featured on Sandatlas are from Sepp’s own rock and mineral collection, assembled from numerous geological expeditions to places including Estonia, the Nordic countries, the United States, Cyprus, Morocco, France, and Ireland.
One of the main pages on Sandatlas is “Complete Guide to Rock Types: Igneous, Sedimentary, Metamorphic”. Forty-six igneous rocks are listed, with brief descriptions, and 30 of them have links to their own page with a more detailed description and lots of interesting photos. Thirty sedimentary rocks are listed (19 having their own page), and 27 metamorphic rocks (16 with their own page). I assume Sepp intends eventually to provide pages for all the listed rock types. In general, the coverage is selective but is nevertheless impressive.
Another main page is “Rock Forming Minerals”. This is a very long page and is much more technical than the rock types section. It’s more like what you would find in a geology textbook, but in my view it is well organised, well explained and well illustrated. If you want to gain an understanding of the chemistry and character of something like framework silicates, or the garnet group, or corundum, this is a great place to go to. How and where minerals form is covered along with the general traits of hand specimens. Field tips, weathering and environmental notes are usually provided. These help to make the technical information more useful to the likes of you and me.
There’s a lot 0r interesting stuff on Sandatlas, although it’s not always easy to find. At the end of the home page is a list of articles that explain key geological concepts and natural processes. This includes such intriguing topics as “How Geologists Identify Rocks”, “What is Opaque Color”, and “Do Rocks Really Fit Into Three Categories?”. At the end of each article is a folder icon with one or two names of Sections in the website – if you click on these Section names, you will be taken to lists of other articles that are otherwise hard to identify.
“Rocks are not silent,” writes Sepp in the “About” page of Sandatlas. “They carry the memory of oceans long vanished, volcanoes that once shook the sky, continents that drifted across the planet. Learning to read them is a way of regaining closeness to the Earth. When we look at nature with understanding rather than indifference, we begin to value it – and we protect what we value.” He continues: “Sandatlas is a bridge between curiosity and knowledge, between observation and insight. It… exists for the broad community of curious minds – hikers who pause at a cliff face, photographers drawn to patterns in stone, collectors who turn over pebbles just to know what they are. It is here for anyone who suspects that the landscapes they walk through are more than just scenery.”
The next in this Series is “A Review of ‘New Zealand Geographic’ Magazine Online“. An Index to this Series is here.
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