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dancingfish
You should be able to make out the chunks of quartz embedded in the stone
Look closely at the stones and you will see how much quartz they are composed of.
Similar rock is found round the south of the island. Around 65 million years ago volcanic eruptions around Arran forced molten lava through fissures in the sandstone. The extreme heat metamorphosed the sandstone, baking it white and producing a quartzite rock.
It makes the stones sparkle really beautifully through the moss.