Mariposite

Mariposite is not a recognized mineral but a chrome-rich varioety of phengite, which is a silica-rich variety of muscovite, a mica.

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Mariposit mariposite
Mariposite from Eureka District, Trigo Mountains, La Paz County, Arizona

Origin of name: named by American chemist and geologist Benjamin Silliman it´s type location: Mariposa County, California

Synonyms and trade names: chromphengite

Localities: mostly in the USA. Other locations are Canada, Venezuela, China, Japan, Egypt, Ireland, France and Spain.In Austria one deposit is known on the north slope of Brennkogel mountain in the High Tauern range.

Handling: due to the very low hardness and it´s perfect cleavage mariposite is not suited for use in jewellery

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Gemmological Properties of Mariposite

Formula:
K(Al,Cr)2(Al,Si)4O10(OH)2
Crystal system:
monoclinic
Mohs hardness:
2.5
Specific gravity:
2.77 - 2.88
Refractive index:
1.552 – 1.616
Max. Birefringence:
0.0340 – 0.0420
Dispersion:
weak to distinct
Pleochroism:
weak
Luminiscence:
none
Lustre:
vitreous, silky, pearly
Cleavage:
vollkommen
Fracture:
micaceous
Colour:
light to dark green