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I don't know the particulars of that sample but the individual xtls are one thing. Often times the actual media is made up of xtls that are fused together to make the actual media so that clump you...

That is Chrome Oxide. Those particles are actually individual crystals. Hexoctahedral if I recall correctly for Chromite probably a variation for those in the picture.

The carbonate would also be way softer than the oxide so figure that into the mix too.