They showed many similarities, he said, including the spherules, calcium sulphate veins and fine-grained structure.

BBC: Opportunity and Curiosity find similar rocks on Mars

The rocks contain very fine-grained sediments but are cut through with pale veins of what could be calcium sulphate.

BBC: Curiosity Mars rover takes historic drill sample

The John Klein slabs contain very fine-grained sediments but are cut through with pale veins of what could be calcium sulphate.

BBC: Curiosity Mars rover spins its rock drill

Then a solution of calcium and water is applied by a modified winter gritting machine with a very fine sprinkler-like system attached.

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