vitrain
/ˈvaɪtreɪn/
noun
- A shiny, black, glassy type of coal that breaks into smooth, angular pieces.
- The miner held up a piece of vitrain, noting its bright, reflective surface.
- Vitrain is often the hardest and most lustrous component of bituminous coal.
- Under the microscope, vitrain shows a structure similar to charcoal.