A great diversity of interesting and beautiful stones can be found on the coastline that runs north from Gemstone Beach near Orepuki in Southland, New Zealand. In this Series, 30 recently polished stones from that beach are described. They also illustrate some of the challenges a tumble polisher faces to obtain a completely smooth and well-polished stone. These 30 stones were selected from the smaller stones in batches tumbled in two 3lb barrels. As a result of looking closely at these stones, I realise the need to pay more attention to my inspection of stones before they pass onto the next stage of tumbling. And I need to re-examine 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, Part 2 dealt with Stones 6 to 10, and Part 3 examined Stones 11 to 15. The five stones featured here are slightly smaller than the first 15.
Stone 16 is perhaps one of the most beautiful four stones of the 30, and in addition it is among the best polished. It is a hematite jasper with some white quartz in it.
I have noticed that the brightest of the red jaspers on Gemstone Beach tend to have hematite in them. The following is taken from a November 2023 TumbleStone Blog Post on a Gemstone Beach hematite jasper: As Britannica notes, hematite is a heavy and relatively hard oxide mineral, ferric oxide (Fe2O3). It makes up the most important iron ore because of its high iron content (70%) and its abundance. Its name is derived from the Greek word for “blood,” alluding to its red colour. I recently read the following comment made by Tim Weglarz on the “Great Lakes Rocks & Minerals” Facebook Group: “The grey metallic bands and red coloration… of jasper is from hematite. When hematite occurs as megascopic flakes, it is opaque and metallic. When it occurs as microscopic flakes dispersed in silica, it is translucent and blood red… The red jasper… has much smaller amounts of much finer grained hematite than the opaque metallic bands.” See “H is for Hematite Jasper” in this Post for a brief description of hematite jasper generally.
Stone 17 has some fascinating veins, white and green, which caught my eye on the beach. It is tempting to think it is jasper but not all dark red rock is. The dark red is due to the presence of iron oxide, and this can occur in a number of rock types. Stone 17 has lots of tiny quartz crystals in it, so it may be a form of quartzite.
Much of Stone 17 has not taken a good polish and it lacks shine but the veins are clear and detailed.
Stones 18 and 19 also did not tumble polish well. Stone 18 is very likely to be a jasper, and sometimes jaspers like this, with lighter coloured material, do not polish well.
An idea of varieties of jasper and difficulties in tumble polishing them can be found in “Diane’s Stone, and an Introduction to Jasper”.
Stone 19 has a variety of material in it, some of which appears crumbly and did not not take a shine.
It was the pink in the stone that caught my eye on the beach, but I have mixed success in polishing such stones. Usually I am able to cull crumbly stones at an early stage in the tumbling process through the inspection I undertake between stages. However, sometimes my optimism that a stone will turn out to be ok overrides my critical judgement.
Stone 20 is a gorgeous little jasper that I struggled to get good images of. Perhaps the sunlight was not bright enough, or maybe the slight roundness of the surfaces introduced subtle reflections. Unlike most of the other stones, which had two main faces, Stone 20 has three main faces.
Hematite is again present in the stone, and I suspect it contributes to the bright yellows, oranges and reds.
Part 5 in this Series examines Stones 21 to 25.
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