What is "roscoelite"

Roscoelite \Ros"coe*lite\, n. [From an English chemist, H.E. Roscoe + -lite.] (Min.) A green micaceous mineral occurring in minute scales. It is essentially a silicate of aluminia and potash containing vanadium.

n. (context mineralogy English) A monoclinic-prismatic mineral containing aluminum, hydrogen, magnesium, oxygen, potassium, silicon, and vanadium.

Roscoelite is a green mineral from the mica group that contains vanadium. The chemical formula is K( V, Al, Mg) Al Si O(O H). Crystals of roscoelite take on the monoclinic form, and are from the 2/m point group. The appearance is semi transparent to translucent coloured olive brown to green brown. The lustre is pearly. The mineral shows pleochroism with X showing green-brown, and Y and Z axes showing olive-green colour. The mineral was named after Henry Enfield Roscoe who first produced vanadium metal.