English: Gilsonite from the Tertiary of Utah, USA. (~7.4 centimetres (2.9 in) across at its widest)

Gilsonite (a.k.a. uintaite) is a variety of asphaltite - it's a solid hydrocarbon - basically solidified oil. Gilsonite usually has the appearance of obsidian or anthracite coal. It is jet black in color, very lightweight, brittle, and has a conchoidal fracture. The largest “deposits” of gilsonite in the world are in the Uinta Basin of northeastern Utah, USA. Gilsonite occurs there as vertical NW-SE trending veins intruded within the Eocene-aged Uinta Formation. The source of the hydrocarbons is organic-rich beds in the underlying Green River Formation (Eocene) and Wasatch Formation (Paleocene).

Gilsonite is not readily combustible and is not a fuel, but it does have economic value. Gilsonite is mined in northeastern Utah and processed and is used in numerous products and applications (e.g., see: www.geospectra.net/kite/gilsonite/gilson.htm).

Seen here is a gilsonite sample from the Big Bonanza Vein (also known as the Independent Dike or the Independent Vein; other names for the same dike include East Bonanza Vein and Bonanza Vein; the latter designation has been applied to more than 1 gilsonite vein in the area). The dike ranges from about 5 to 14 feet wide and averages over 10 feet wide over a 3 mile stretch. It intrudes the Uinta Formation and was probably emplaced ~10 to 30 million years ago.

Locality: unrecorded/undisclosed locality along the Big Bonanza Vein (Independent Dike), near the town of Bonanza, eastern Uintah County, northeastern Utah, USA