Vitrain

Vitrain is a lithotype of coal formed from the bark of large plants. Known for its glossy appearance, vitrain typically occurs in thin bands, between 3 and 10 millimeters in width.^[1][2] It has a brittle texture and typically forms cubical pieces when broken.^[3] Chemically, vitrain stands out among coal lithotypes by hosting large concentrations of germanium.^[4] Combustion of vitrain proves a vital source of germanium production, where the element can be extracted from the leftover ash.

The surface of a vitrain fragment isolated from low-carbon coal viewed under a microscope (x2000 magnification)