I wrote this Review for the October 2025 edition of “StoneSpeak”, the Newsletter of the Southland Geological and Lapidary Club. The following is a slightly fuller version. My first Review of an online resource for “StoneSpeak” was of Peter Ballance’s e-book (2017) “New Zealand Geology: An Illustrated Guide”. The Southland Club’s website is here and its Facebook Page is here.
This website (https://rocksminerals.flexiblelearning.auckland.ac.nz) was produced by the University of Auckland’s Department of Geology in 2005. It provides very good introductory information about minerals and rocks in a New Zealand context. The language used manages to avoid over-simplification and usefully explains many key technical terms about geology and rocks. For example, on Clastic Sedimentary Rocks: “The fragments of pre-existing rocks or minerals that make up a sedimentary rock are called clasts. Sedimentary rocks made up of clasts are called clastic (clastic indicates that particles have been broken and transported). Clastic sedimentary rocks are primarily classified on the size of their clasts” (see first photo below). The website is illustrated with a number of photos of mineral and rock specimens from the University’s Geology Department collection.
When I find a stone on a beach, I often go to Jocelyn Thornton’s book “Gemstones” for help to identify it. Or I post a photo on a New Zealand rockhound Facebook Group, asking for an identification. Often I get a name for the stone, such as argillite or gabbro. I can then go to this University of Auckland website, a more geology-oriented source, to get some information on argillite or gabbro.
There are five sections in this website: Home, The Geology of Auckland, Minerals, Rocks, and Glossary. I have most often consulted the Minerals and Rocks sections to gain an understanding of the types of stones I find on the beach. The most useful parts of the Minerals section are Properties (eight are outlined) and Common Rock-Forming Minerals (21 are described). One of the limitations of the website can be seen here – it doesn’t always do a good job of dealing with the range of types of a mineral or rock (always a difficult task). So its photos of Garnet, for example, are all of one type and don’t include the likes of grossular and hydrogrossular.
The Rocks section includes important Features to look for when writing descriptions and identifying rocks. To take Texture as an example: “Texture refers to the shape, arrangement and distribution of minerals or grains / clasts within the rock – the texture in a geological sense does NOT refer to the roughness of the surface of the rock”. Then 12 igneous, eight sedimentary and seven metamorphic rocks are described. These entries include a basic description, photos of usually one to four specimens (up to seven in a couple of cases), and a list of basic properties. I especially like the chart that is a guide to the identification of igneous rocks based on their mineral composition.
I use this website whenever I want to check out a particular mineral or rock. Its New Zealand focus is its strength, along with its careful balance of technical detail and understandable explanation. I always want it to provide more information, and I wish it had more photos of specimens, but this doesn’t detract from its value.
The next Review in this Series is of Jocelyn Thornton’s (1985) “Gemstones”. An Index to this Series is here.
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