vitrain

noun

1. (countable, uncountable)A constituent of banded bituminous coal consisting of a horizontal glossy band of friable material.

   “The caking behaviour of vitrain and clarain could be improved after the coal has been picked out.”

   “In order to measure relatively accurately the activation energy of coal, and to exclude the disturbance from coal samples, the hand-picked banded vitrains in bright coal are adopted as experimental samples (Table 1).”

   “Thus, it may be concluded that a lower viscosity of plastic vitrain grains facilitates pores to grow and coalesce and grains to stick to one another to create intergrain pores.”