Mariposite is a chromium-rich variety of Phengite which is a discredited name for a mineral series between Muscovite and Celadonite.  In other words, Mariposite is a chromium-rich variety of Muscovite. Mariposite is very similar to Fuchsite which is also a chromium-rich variety of Muscovite. Neither Mariposite or Fuchsite is valid minerals, just varieties of Muscovite. Mariposite is colored a distinctive green by the presence of chromium and is often found mixed with white dolomitic marble and Quartz. This combination of deep green and bright white makes for an attractive cabochon (see picture above). Mariposite was named for Mariposa County, California, USA, where it was originally found, though it can be found in several locations in the Sierra Nevada mountains of California. It has also been found in a few locations in Newfoundland, Canada, where it is locally called Virginite.

Chemical Formula: K(Al,Cr)2(Al,Si)4O10(OH)2
Potassium Aluminum Chromium Silicate Hydroxide
Molecular Weight: 521.21 gm
Composition: Calcium 23.07 % Ca 32.28 % CaO
Boron 12.44 % B 40.07 % B2O3
Hydrogen 3.09 % H 27.65 % H2O
Oxygen 61.39 % O
  100.00 % 100.00 % = TOTAL OXIDE


Crystallography: Monoclinic – Prismatic
Crystal Habit: Crystals tabular to columnar || [001], striated || {001}, pseudohexagonal or diamond-shaped. As stellate aggregates, plumose, globular; scaly, granular, compact massive.
Twinning: Composition plane {001}, twin axis [310], forming six-pointed stars.


Cleavage: Perfect on {001}, partings on {110}, {010}
Fracture: Micaceous
Tenacity: Laminae flexible and elastic; tough.
Moh’s Hardness: 2.5 
Density: 2.77 – 2.88 (g/cm3)
Luminescence: None
Radioactivity: Barely Detectable; GRapi = 140.52 (Gamma Ray American Petroleum Institute Units)


Color: Light to dark Green
Transparency: Opaque
Luster: Vitreous to Pearly or Silky
Refractive Index: 1.552 – 1.616  Biaxial ( ? ) 
Birefringence: 0.0340 – 0.0420
Dispersion: Weak to Distinct; r > v
Pleochroism: Weak