The second revised edition of the photobook “The Trace Fossils of Gemstone Beach” includes two pages of photos of other stones that I have collected from Gemstone Beach. I will try to identify them for readers. Most of the types of stones mentioned are well covered by entries in the book “What’s This Stone? A Photographic Collection of Finds from Gemstone Beach”.
As a tumble polisher, I collect stones primarily for how they look. Stone identification is not always straightforward. Sometimes a stone will clearly fit into a particular type. I am very familiar with a few beaches in the South Island, having spent a lot of time on them and having spent time finding out about their stones – that helps a lot. But it is not unusual for me to come across a stone that defies easy identification. There is such a diversity on some beaches that identification can be a real challenge. It is a stone’s visual characteristics that attracts me, even if I don’t know what it is – but having an identification seems to settle my mind most fully about a stone.
On Page 22 of “The Trace Fossils of Gemstone Beach” (second edition) are these 11 stones, which I will comment on below. I will also note the Blog Post in which they previously appeared so you can look that up for more detail if you wish. Note that the stone numbers don’t appear in the book but will assist you to know which one I am discussing here:
#1 – Probably a mossy kind of jasper with some quartz in it and an interesting cream-coloured vein, found on Gemstone Beach in February 2023. It featured in the 2024 TumbleStone Calendar.
#2 – An opaque hydrogrossular garnet found in front of the carpark in September 2024.
#3 – Unusual spotted stone, probably igneous, similar in character to spotted argillite but likely not a mudstone. Found prior to August 2023 (which is when the photo was taken) but unable to locate just when. See close-up photo below, after the entry for #5.
#4 – A banded form of rhyolite, reasonably common along the south coast of the South Island. It is sometimes called a galaxy stone as it’s like looking into deep space. It was suggested to me that the origin of these stones was likely not to be lava flow but welded ignimbrite.
#5 – I’m not sure what this stone is. Up close, you can see tiny light and dark coloured fragments, which could make if a breccia. I found it in March 2026. Close-up photo below, right.
#6 – This pink stone could be thulite or rhodonite – see the pinks of March in the 2026 TumbleStone Calendar for background on these two types of stones. I found this particular one in March 2024 though it does not appear in the Blog Post for that day.
#7 – This speckled stone is amygdaloidal. The white and pink specks are zeolite minerals that have collected in tiny gas bubble holes in the igneous rock, which is most likely basalt. The resulting in-filled holes are called “amygdales” from the Latin and Greek words for almonds because of their often almond-like shape (see the section on amygdaloidal stones near the beginning of this Post). However, amygdales can also be round and some can be irregular shapes, as shown in this stone (see close-up photo after the entry for #8). I found it in April 2023 but again it does not appear in the Post for that day.
#8 – This is what is usually referred to as a poppy jasper, found in March 2024. It was one of four poppy jaspers that appeared in the month of April in the 2026 TumbleStone Calendar. Poppy jaspers are viewed as orbicular, the orbs forming in concentric layers around a nucleus or central point. But I have also seen them described as spherulitic, made up of small spheres with a thread-like radiating structure. Close-up below right:
#9 – This is an igneous stone, maybe dolerite, with white crystals of feldspar and some green staining likely to be from epidote. The size of the crystals make it a porphyry, meaning it has slowly cooled underground, forming the larger crystals, before coming to the surface to complete cooling more quickly. I found this stone in February 2022.
#10 – In February 2023, I found this breccia on Gemstone Beach. Dark-coloured angular fragments of various sizes have been cemented together in a fine-grained matrix. The fragments seem very fine-grained, maybe from a mudstone, but I am not sure.
#11 – The green in this stone is the typical pistachio green of the mineral epidote. In rocks like epidosite, epidote mixes with quartz and traces of other minerals. In this stone, found in March 2024, there are some tiny quartz pieces amongst the green but the bright white opaque mineral making up the larger pieces is unusual – I don’t know enough to guess at what it might be.
Page 23 features another 11 stones from Gemstone Beach.
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