I sometimes get requests from people wanting to know if I can identify a stone for them. For a range of reasons, it can be difficult to be helpful. For example, photos sent with messages or emails are often not clear enough, and I sometimes need to handle a stone personally to get a good sense of it. Often a number of possible identifications can exist. And I may not be familiar with the area that a stone has come from. My own “expertise” is limited, specific to a handful of beaches. I sometimes share photos of my finds to the Facebook Group “New Zealand Lapidary, Rocks, Minerals, Fossils”. Recently I posted photos of a stone I had found on Kakanui’s Seadown Beach (see photos below), which I called a quartzite. Conor, a Group member from Hawke’s Bay, commented on it, raising the issue of identification in general.
Colourful Kakanui quartzite.
Conor stated: “I am struggling with terminology around rocks. So much confusion around quartz, chalcedony, agate, chert, jasper and flint. U showed a rock and said it was a quartzite. It’s very pretty, I was wandering how to ID a rock as quartzite. I have some similar from the Elsthorpe region in Hawkes Bay but often just called it jasper. I am still learning and it’s very confusing.” For a rockhound, the difficulty with terminology is real, confusion is very common, and it takes time and effort to get past these. And I suspect that, even for the long-time stone collector, there are always stones that resist identification.
I have made the following statement in my recent Series of Posts “Gemstone Beach and Its Stones: An Introduction For The Passing Motorist”, trying to explain the basis on which I have identified many of the stones in that Series: “Over the past six years I have visited Gemstone Beach more than 150 times, also walking further along the Te Waewae Bay coast. But I am not a geologist – I am an amateur beach stone collector and polisher. I have done some reading and research about different types of stones, but my knowledge is limited and often open to correction. There is an amazing diversity of stones on that beach, each unique in some way. In these Posts, I am sharing what I know – it is not expert knowledge and it is not comprehensive.” I further wrote in Part Four of that Series: “To identify for certain what kind of rock a stone is, a mineralogical analysis is needed, a technical and expensive process. The person who picks up a stone on the beach must guess its identification by its appearance, an often imprecise process highly dependent on the person’s previous experience and knowledge. An experienced rockhound learns from published and online sources, other rockhounds, members of Rock and Mineral Clubs and Facebook Rockhound Groups, and specimens viewed in museums and private collections. That is how I learned to identify certain types of stones on Gemstone Beach. But this knowledge tends not to reflect reliable technical scientific analysis of the stone but “local knowledge”, informed as best it can be by a range of sources, but ultimately tentative and fallible. There are also many stones that will not be able to be identified easily, if at all.”
Different types of rockhounds and stone collectors have different purposes, and these influence the significance of identification to them. I am a tumble polisher and collect stones that attract my attention visually. What I see when looking at them is of the most importance. Knowing their identification is not very important at all, except maybe in informing me of how hard the stone is and therefore how well it might suit tumble polishing. However, having said that, there is always a curiosity about what kind of stone I have found, and making an identification just seems to settle something inside me. So I have ended up doing a number of things, as noted above, to identify my finds. Other stone collectors, of course, are interested in developing a collection covering a particular type of stone, or maybe a number of types, or a representative sample for a region or country. For them, identification is much more important and they will expend more time and energy on it than I will.
So, in my view, the keys to developing an ability to identify at least some stones include the following:
1) Spending time getting to know an area (or small number of areas) well. Stones are particular to an area – a beach, a river, a region – and each area has its own distinctive stones and geology. I well remember having to learn the difference between rhyolite and petrified wood at Slope Point – a lot of the banded rhyolite there looked like petrified wood to me, and I had to get used to the fact that a lot of Slope Point petrified wood is black (this Post from 2021 reflects an early stage in my understanding of these distinctions). I learned a lot from a local rockhound who patiently spent time with me there. I usually visit four beaches on my fossicking trips to the South Island – Ward Beach in Marlborough, Kakanui’s Seadown Beach in North Otago, and Southland’s Slope Point and Gemstone Beach. These are beaches with lots of interesting stones but also each of them is very different, with a distinctive bunch of stone types which I am still developing an appreciation for and understanding of. The variations within each stone type continue to amaze me, and I am far from being able to identify more than a few of the stone types there. If you show me a stone from one of those four beaches, there is a chance I might be able to identify it. If you show me a stone from a beach I have never visited, I am likely to flounder, unless it is clearly a common kind like quartz and jasper.
2) Online sources. There are online sources that provide good information about types of stones, different areas, geology, and so on. Spending some time with Google or another search engine will put you onto these. At one end of the spectrum, for example, is Jocelyn Thornton’s “Gemstones”, originally published in booklet form, providing information about types of stones to be found in selected areas of New Zealand. Then there is the University of Auckland’s “Geology” site which provides overviews of different types of rocks and minerals from a geology point of view. And Geology.com, a United States based site providing well-illustrated information about a wide range of stones and rocks. Then at maybe the far end of the spectrum is Mindat which describes itself as “the world’s largest open database of minerals, rocks, meteorites and the localities they come from”. In general, there are very few online sources that identify specific stones from specific beaches.
3) Published sources. I am a book person, once having been a university academic, and I can afford to buy books from time to time. There are very few, if any, books that will quickly identify one of the stones you find, but they can help you with clues to identification and build up your general background knowledge. I mention four local books I have found useful towards the end of the TumbleStone Two home page. Parts of my home library are in the photos below:
4) Other rockhounds. I have been fortunate to meet and spend time with a number of people who share my interest in “pretty stones”. Many of these people have a depth of knowledge about a beach and its stones and have taught me about them. They in turn have often learned from other local rockhounds. This has two implications. First, they have a good understanding of local stones and the identification of many of them. Secondly, they are reliant on local knowledge that sometimes might use different terms than people in other areas. And some of those terms might be misleading. For example, I am not sure that what locals call “fossil worm casts” on Gemstone Beach are actually trace fossils of “worm casts”. My research into trace fossils suggests that a range of small animals can leave behind such traces. I’m still working on this. And that is the nature of identification skills – they are always a work in progress.
5) Members of Rock and Mineral Clubs and Facebook Rockhound Groups. There are a number of Clubs in New Zealand, in various stages of growth and activity – see the Otago Club’s listing of Other Clubs and the Affiliated Clubs of the National Association of New Zealand Rock and Mineral Clubs. Meeting other people with the same passion is great! And you can learn a lot. Clubs often have a programme of regular events, including field trips, and some have their own newsletter and website. Some have cutting and other lapidary machinery available for members to use as well. I am currently a member of the Southland Geological and Lapidary Club.
6) Specimens viewed in museums and private collections. I have been fortunate enough to visit a handful of impressive stone collections, including Vince Burke’s Birdling’s Flat Gem Museum, Jack Geerlings’ collection in Winton (see towards the end of this Post), and Malcolm Luxton’s Agate Orphanage in Ashburton. I have also viewed Museum collections especially in Southland, such as Te Hikoi in Riverton Aparima. Other stone collectors have also shared their stones and stories with me. I first learned about quartzites, for example, from Vince Burke’s display of these stones.
I sometimes get into a conversation with a fellow fossicker and tumble polisher along the following lines: “What do you think this is?” “It could be a hydrogrossular garnet, but I’m not sure.” “It kinda looks like it, but it doesn’t feel like it.” “It could be quartz.” “But quartz doesn’t usually have that colour in it.” “It feels cool like quartz often does.” “Do you think I should put it in my bag?” At that point, you have to come back to the point of the fossick. I tend to say: “If you’re simply collecting hydrogrossular garnets, then it’s probably not a good specimen if you’re unsure about its identification. But if you like how it looks and think it will tumble polish well, then by all means put it in your bag.”
Reflecting such a conversation, I wrote the following on the TumbleStone Two page on hydrogrossular garnets: “Hydrogrossular garnets are probably the most sought after stones on Gemstone Beach. I often find it hard to walk past even the tiny ones, partly because they shine so brightly. To find a larger one is always a thrill. But I still have to check each possibility carefully, as some turn out to be quartz and others turn out to be argillite – the angle of the sun can make identification deceptive. Most hydrogrossular garnets have a waxy feel, and they lack the crystalline character of quartz – it takes a while to develop a feel for their subtle differences. I am grateful to those fossickers I have met on Gemstone Beach who have shared their knowledge with me, some of whom have even given me specimens they have just found. And seeing stones in museums and private collections has also been very important in helping me to spot stones on the beach.” Later on that page, in a section on “Identification”, I observed: “There seems to be some disagreement even amongst experts, over whether a stone is a hydrogrossular garnet or not. For example, in August 2020 I posted a photo of a Gemstone Beach stone online, suggesting it might be a hydrogrossular garnet but noting that I wasn’t sure. Someone in North America who had undertaken technical analysis of ‘hydrogrossular’ garnet stones from New Zealand stated that most of them were in fact ‘grossular’ and that my stone was most likely ‘grossular’. But in the same discussion thread, a geological research technician from a New Zealand university had no hesitation in stating “It’s a ‘hydrogrossular’ for sure”, as did a number of amateur rockhounds familiar with Gemstone Beach.” At the end of that section, I had to admit: “The information and stones presented here are basically reflective not of reliable technical scientific analysis but of ‘local knowledge’, informed as best it can be by a range of sources, but ultimately tentative and fallible.”
I write TumbleStone Blog mainly for myself. It provides an excellent record of stones that I find and polish. Even if I misplace or give away a stone, I still have its photos on the Blog. I also have a retrievable record of the research I do on different stones. It can be easy to forget something I’ve read – but if I put it in a Blog Post, I can always go back to it. The Blog contains identifications of many of the stones I have found, but I often state “probably” or “I guess” or “perhaps” because my identification is often uncertain. I sometimes provide the sources for an identification so that readers become aware of this, can check the sources and evaluate the ID for themselves. Earlier Posts in my Blog were written when the state of my knowledge was not well advanced – keep that in mind when reading them. I try to correct obvious errors. Current Posts reflect my current understandings, and these will change in the future.
Colourful Kakanui quartzite.
So, why is that red and yellow stone (see above) a quartzite? When I picked it up on the beach, I thought it might be a jasper, because of its colour. And there are some very nice jaspers on Seadown Beach. But it felt a little different, not as smooth as I expected. And there are in fact more quartzites than jaspers there. But it didn’t have the mineral “clouds” and clarity often found in quartzite. I decided it was a quartzite only after looking at a photo of it in detail – tiny clear bits of quartz can just be seen in it, and Seadown Beach quartzites (such as the yellow ones) often have tiny clear quartz crystals or fragments in them (see photos above).
Kakanui quartzite with tiny translucent bits of quartz in it.
Kakanui quartzite with tiny translucent bits of quartz in it.
But how do I know those yellow stones with tiny clear quartz in them are quartzites? And how do I know quartzites can come in red and yellow? Both bits of knowledge go back to what I learned from Vince Burke’s Birdling’s Flat collection, build up by him and his family over years of fossicking on Birdling’s Flat. He had a bunch of stones in his Museum that he labelled as “Quartzites”, including these distinctive yellow ones that I have now seen at various beaches along the Canterbury and Otago coast (and even the odd one in Southland), but I don’t know how he learned that identification of those stones. From fellow fossickers? From a geologist? From a book?
Conor, the person who sparked this Post (see the beginning, above), is correct when he refers to the confusing terminology around quartz, quartzite, chalcedony, agate, chert, jasper and flint. They are all varieties of quartz in different forms (see Geologyin), and there are often regional differences in terminology. Geology.com notes: “Flint, chert, and jasper are names commonly used by geologists and by the general public for opaque specimens of microcrystalline quartz. The same hand specimen might be called ‘chert’ by one person, ‘flint’ by another, and ‘jasper’ by a third.” Outside of New Zealand, “agate” refers to a type of chalcedony (microcrystalline quartz) which occurs in gas bubble spaces in volcanic rocks, growing inwards from the walls of the cavities and usually marked by concentric colour bands – but in New Zealand, plain stones of chalcedony are also often referred to as agates. “Quartzite” is a term that has been used for a very hard but unmetamorphosed sandstone that is composed of thoroughly cemented quartz grains. Such a sedimentary rock is sometimes called “orthoquartzite”. This distinguishes it from the type of rock that is more commonly called quartzite, a metamorphic rock in which the grains are not apparent at all, sometimes called “metaquartzite” to emphasize its metamorphic origins (see Wikipedia). There seems to be a wide variety of types of stones that I have learned to call quartzites and I am not at all sure what they really are.
Our stone identifications usually need to be seen as tentative and fallible, but we really do like to be able to put a name to a stone.
