Due to its high carbon content, jet is classified as a type of coal. It is a compact substance found in bituminous shales, and it produces a brown streak. Jet has a conchoidal fracture, and it is hard enough to take a good polish, a characteristic that has been exploited for making jewelry and ornaments. It rarely forms in geographically extensive seams.

TEXTURE When examined in close detail, jet shows woody tissue structures.

ORIGIN The formation of jet has been open to debate. It is generally believed that this black, coal-like rock developed in marine strata from logs and other drifting plant material, which then became waterlogged and sank into the mud on the seabed. It is found in rocks of marine origin, unlike other forms of coal, which form from plant matter accumulated on the land surface.

Grain size: Medium, Fine

Classification: Organic

Fossils: Plants

Grain shape: None