Gilsonite

Glisonite is a black, pitch-like substance which occurs in pure form in large veins in the Tertiary sediments of the Uinta Basin. It is a homogenous petroleum substance (technically it is a predominently aromatic asphaltite) which fuses relatively easily and burns like tar. Glisonite is brittle and has a distinctive conchoidal to hackly fracture. Fresh glisonite has a brilliant black luster, but weathered glisonite and some of the more refractory varieties have a dull, soot-black appearance. Glisonite has a specific gravity of 1.07, just slightly denser than water, and a hardness of 2 to 2.5 on Moh's Scale. Glisonite is soluable in asphalt-based petroleum, and is frequently employed to change the consistency of lighter petroleum products. Finely pulverized glisonite is chocolate brown in color and exceedingly penetrating to the skin and lungs.