The sample is from the Stac Fada member, a suevite from the Stac Fada impact event, with hit somewhere in the region of NW scotland around 1.2 Billion years ago. The melt clasts in this sample are quite small, but you can see 1cm scale circular clasts called ‘accretionary lapilli’. These are formed when dust from the impact clumps together in the atmosphere, usually around moisture droplets, and rains-down like hailstones. If these fall into a density current, like has happened here, they are carried in the flow and spin, collecting more and more dust in the flow like a rolling snowball - these develop the concentric circular layers you can see here. The suevite also contains larger clasts of Lewisian gneiss, the target-rock.
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