In this Series, 30 recently polished stones from Gemstone Beach/Te Waewae Bay are described. They illustrate the great diversity and beauty of stones that can be found on this beach, as well as some of the challenges a tumble polisher faces to obtain a completely smooth and well-polished stone (if that’s their aim). These 30 stones were selected from the smaller stones from batches tumbled in two 3lb barrels. Initially I thought all the stones in these two batches ended up nice and smooth. However, looking at their photos, I noticed tiny holes, bruises, scratches and rough patches on many of them. I need to pay more attention to my use of cushioning filler in the latter stages of the tumbling process. Part 1 in this Series of Posts described Stones 1 to 5 and Part 2 dealt with Stones 6 to 10. The five stones featured here are slightly smaller than the first ten.
Stone 11 is a small grey stone with a faint hint of blue.
When I saw it on the beach, the thin dark veins stood out. Later, while turning the stone for photographs, sunlight glinted off a couple of small areas, probably mica crystals. Some can be seen at the bottom right in the close-up of Side A above.
Stone 12 is a variation of spotted argillite, as is Stone 3 (see Part 1) and Stone 14 (below).
Stone 12 is darker in colour than Stone 3, and its “spots” are slightly more clearly defined. There is quite a range of spotted argillites on Gemstone Beach.
Stone 13 is an astonishing cluster of small white spots. They are packed tightly together.
This is likely to be a volcanic stone, originally full of tiny gas bubbles. Those bubble holes (“vesicles”) were infilled slowly by a white mineral as hot water flowed into them. These white “spots” are called “amygdales” (or “amygdules”), from the Latin and Greek words for almond, reflecting the almond-shape of many such spots. Stones W30 to W33 in this Post are other examples of amygdaloidal stones from Gemstone Beach, and a more detailed explanation of their formation follows them.
Stone 14 has some similarities to Stone 3 – a dark green fine-grained sedimentary stone with seemingly out-of-focus light-coloured spot-like patches.
They are both most likely to be types of spotted argillite (along with Stone 12). Stone 14 also has some very fine veins in it, some dark and some light. At first sight, it is tempting to think Stone 14 could be a “variolite”, because of its appearance. Variolites contain small spherical or globular structures, called varioles, in a fine-grained matrix. Varioles are lighter coloured than the host rock and the photo of a specimen on Wikipedia looks very similar to Stone 14. However, variolites are volcanic in origin, usually basaltic. Mindat notes that varioles have quite a different origin than spherulites, which are also small rounded bodies that commonly occur in igneous rocks (such as spherulitic rhyolite, as can be found at Slope Point – see, for example, the second stone in this Post).
Stone 15, like Stone 4 and Stone 9, is volcanic in origin with light-coloured crystals in it. Unlike Stone 4, the crystals are densely packed and in contrast to Stone 9, the surrounding rock material is not as dark.
The tiny often oblong crystals in the stone are fascinating, and scattered amongst them are some black and some silver (mica?) crystals:
The next Post in this Series examines Stones 16 to 20.
TumbleStone 
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