I found this small stone on a beach on the east cost of the North Island in New Zealand. It's red/brown and has almost gray spots, but also has lots of white crystals coming out of it. It has a dull shine to the whole thing but the white crystals sparkle. For it's size (I'd estimate about 3-4 cm) it seems quite heavy.

polka dot stone

polka dot stone2

Also does anyone have any quick tips for me to help clean it up a bit?


closed as off-topic by Leukocyte, Fred, daniel.neumann, trond hansen, arkaia Aug 28 at 17:24

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This is most likely a piece of greywacke with some pieces of quartz. It's been rounded by wave action (or also river action, since it may have been carried to the sea from where it's exposed in the mountains). Greywacke is New Zealand's most common basement rock ; it was deposited in a giant fan off a continental shelf and then scraped up onto the Australian Plate by convergence with the Pacific Plate. Person27 is probably right to suggest that the red color is from staining.

Te Ara website: https://teara.govt.nz/en/map/9063/greywacke-in-new-zealand


I think the white is probably quartz, which is common on many beaches, though someone can correct me if they know about New Zealand geology. The faint red lines are probably staining from weathering and the rock itself could be igneous. The rest is probably granite or other common rock, and it may look darker than a non-weathered sample would.


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