Triphylite

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Triphylite crystal in matrix, collected from Smith Quarry (Chandler Mills Quarry), Newport, New Hampshire 43°21′28″N 72°15′8″W / 43.35778°N 72.25222°W / 43.35778; -72.25222[1]
General
Category	Phosphate minerals
Formula (repeating unit)	LiFePO4
IMA symbol	Trp[2]
Strunz classification	8.AB.10
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pmnb
Unit cell	a = 6.0285(6) Å, b = 10.3586(9) Å, c = 4.7031(3) Å, Z = 4
Identification
Color	Green–blue gray, brown–black
Crystal habit	Massive, granular, prismatic
Cleavage	{100} perfect, {010} imperfect, {011} poor
Fracture	Uneven–subconchoidal
Mohs scale hardness	4–5
Luster	Vitreous–subresinous
Streak	White–grayish white
Diaphaneity	Transparent–translucent
Optical properties	Biaxial (+), 2V = 0°–65°
Refractive index	nα=1.675–1.694, nβ=1.684–1.695, nγ=1.685–1.700
Birefringence	δ = 0.0060–0.0080
References	[3][4][5]

Triphylite is a lithium iron(II) phosphate mineral with the chemical formula LiFePO₄.^[6] It is a member of the triphylite group and forms a complete solid solution series with the lithium manganese(II) phosphate, lithiophilite. Triphylite crystallizes in the orthorhombic crystal system. It rarely forms prismatic crystals and is more frequently found in hypidiomorphic rock. It is bluish- to greenish-gray in color, but upon alteration becomes brown to black.