What are rock grains/the grains in rocks made out of?

Distance^2= yellow line ^2 (see picture) = 30^2 + 49^2so distance = squareroot of (300^2 +49^2)i dont know if this is how to solve it, but i cnt think of another way

Ireally don’t know

Answerapplying a direct current to a non magnetic material in order to create a electromagnetic field; plz check first good luck;

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