Microscopic specks of covellite, just little sparkles really, but richly covering the nooks and crannies of this massive volcanic rock (pumice?). The really neat thing, honestly, is the label dating these to the famous 1760 eruption of mount vesuvius!!!! Two pieces, actually, come with the single label 4.7 x 2.5 x 2 and 7.2 x 6.7 x 3.5cm