Triplite

Triplite is a rare phosphate mineral with formula: (Mn, Fe)₂PO₄(F, OH). It occurs in phosphate-rich granitic pegmatites typically as irregular brown opaque masses. Triplite was first described in 1813 for an occurrence in Chanteloube, Limousin, France.^[6] The name is from the Greek triplos for triple, in reference to the three cleavage directions.^[3] In color and appearance, it is very similar to rhodocrosite, another manganese bearing mineral. Chemically, it is also quite similar to triploidite the difference being that triplite is fluorine dominant while triploidite is hydroxide dominant.

Triplite
Triplite from Alchuri, Shigar Valley, Baltistan, Pakistan (1.2 × 1 × 0.9 cm)
General
Category	Phosphate minerals
Formula	(Mn,Fe)2(PO4)(F,OH)
IMA symbol	Trl[1]
Strunz classification	8.BB.10
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	I2/a (no. 15)
Unit cell	a = 11.97 Å, b = 6.52 Å c = 10.09 Å; β = 105.62°; Z = 8
Identification
Color	Chestnut to reddish brown, flesh-red, salmon-pink
Crystal habit	Prismatic, massive to nodular
Cleavage	Good on {001}, fair on {010}, poor on {100}
Fracture	Uneven to subconchoidal
Mohs scale hardness	5 to 5.5
Luster	Vitreous to resinous
Streak	White to brown
Diaphaneity	Translucent to opaque
Specific gravity	3.5 – 3.9
Optical properties	Biaxial (+)
Refractive index	nα=1.643–1.684, nβ=1.647–1.693, nγ=1.668–1.703
Pleochroism	Distinct; yellow-brown to reddish brown
2V angle	25 – 76°
Dispersion	r > v, moderate to strong
Alters to	Alters to brownish black
References	[2][3][4][5]

Occurrence

Triplite from Colorado

Triplite is a rare fluoro-hydroxide phosphate mineral that forms in phosphate rich granite pegmatites and high temperature hydrothermal veins. It has been found in the United States in California, Nevada, Arizona, Colorado, South Dakota, Virginia, Connecticut, and Maine. Other occurrences include the Shigar Valley, Pakistan; China; Bavaria, Germany; Kimito, Finland and Karibib, Namibia.^[3]