Mariposite (a variety of Muscovite)
Current inventory:  0 gems
 

  
Mariposite is named for Mariposa County, California, USA, where it was originally found.

Discovery date unknown;   IMA status:  Not Valid (a variety of Muscovite)

Chemistry

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

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/H.10-70

Nickel-Strunz 10th Ed. ID:

9.EC.15

9 : SILICATES (Germanates)
E : Phyllosilicates
C : Phyllosilicates with mica sheets, composed of tetrahedral and octahedral nets

Related to:

Chromian-rich variety of Phengite (Muscovite). Mica Group. Muscovite Subgroup.

Varieties:

None

Synonyms:

Chrome-Phengite, Chromphengite

Crystal Data

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.

Physical Properties

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)

Optical Properties

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

Occurances

Geological Setting:

A common rock-forming mineral, in phyllites, schists, and gneisses; in granites, granite pegmatites, and aplites. Formed from other minerals under hydrothermal conditions; may be detrital or authigenic.

Common Associations:

Quartz, Plagioclase, Potassic feldspar, Biotite, Tourmaline, Topaz

Common Impurities:

None

Type Locality:

Mariposa County, California, USA

Year Discovered:

Unknown

View mineral photos:

Mariposite Mineral Photos and Locations

More Information

Mindat.org (Mariposite)
Mindat.org (Phengite)
Mindat.org (Fuchsite)
Mindat.org (Muscovite)
Webmineral.com (Muscovite)

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 are 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.
 

  
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