re: Closeup... sand all right... well...
Doesn't look too much like coal or solidified hydrocarbon, does it? On the other hand, it does strongly resemble miniture blueberries, down to the cleaving into neat halves and possibly quarters as we see in Meridiani.
And, like Meridiani, we see a slight admixture of lighter colored material, possibly sulfate/salts, such as make up the layered deposits at the Opportunity site.