What is Roscoelite?
Roscoelite is a vanadium-rich mica, usually green to olive-brown, valued as a collector mineral and as an indicator of vanadium-bearing hydrothermal systems.
Mineralogy and crystal structure
Reference formula: K(V,Al)2AlSi3O10(OH)2. Roscoelite is a variable mica-group mineral with no exact public COD model selected for this batch. Its composition and polytypism vary, so the guide intentionally does not display a fabricated single lattice. Roscoelite is classified with silicates and has a monoclinic crystal system. Typical hardness is 2–3 on the Mohs scale and specific gravity is approximately 2.6–2.9.
Colour, lustre and habit
Typical colours include green, olive-green, brown-green, black. The usual foliated, micaceous, massive habit and pearly, dull, earthy lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Roscoelite forms in or is associated with hydrothermal veins, vanadium-rich ores, sandstone-hosted uranium-vanadium deposits and altered rocks. Important documented localities include the United States, Mexico, Bolivia, Peru, South Africa and Australia.
Olive-green mica with an ore-deposit story
Roscoelite is commercially distinctive because its muted green colour is tied to vanadium chemistry rather than a simple decorative pigment. Foliation, matrix and locality are central to a good specimen.
Collecting and care
The mica is soft and cleavable. Keep dry, avoid abrasion and do not generate dust from vanadium-bearing material.
