Another tumble-polished stone collected from Gemstone Beach during my “Southern Sojourn” at the start of this year. This one is light-coloured and I wasn’t sure it would polish well – I wondered if it might be too soft. However, it has turned out well, with just a couple of tiny rough areas.
The close-ups reveal fascinating tiny white crystals of a variety of shapes and sizes, along with very thin dark veins. A helpful member of the Facebook Group “New Zealand Lapidary, Rocks, Minerals, Fossils” suggested that this stone is dacite, and I suspect this is likely to be accurate.
Dacite is a fine-grained volcanic rock intermediate between andesite and rhyolite – it usually contains more quartz than andesite and more plagioclase feldspar than rhyolite. It is named after Dacia, a ancient Roman province in Transylvania, Romania. Dacite is lighter in colour than andesite, and contains phenocrysts (the small crystals – probably feldspar – apparent in Stone #4). More information on dacite can be found in Auckland University Geology, Geology.com and Alex Strekeisen.
Go to Stone of the Day #5.
Go to start of the Stone of the Day Series for November.
The FB group members are so helpful aren’t they – just like you!! Really love the pattern and colouring of this stone!
The FB group members are so helpful and knowledgeable- just like you! Love the pattern and colour of this stone!