Lithiophilite

Lithiophilite is a mineral containing the element lithium. It is lithium manganese(II) phosphate with formula: LiMnPO₄. It occurs in pegmatites often associated with triphylite, the iron end member in a solid solution series. The mineral with intermediate composition is known as sicklerite (Li(Mn,Fe)PO₄). The name lithiophilite is derived from the Greek philos (φιλός) "friend," as lithiophilite is usually found with lithium.[2]

Lithiophilite
General
Category	Phosphate minerals
Formula (repeating unit)	LiMnPO4
Strunz classification	8.AB.10
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pmnb (if holohedral)
Identification
Color	Clove-brown, yellowish brown, honey-yellow, salmon-pink, blue-gray, gray
Crystal habit	Prismatic – crystals shaped like slender prisms, stout prismatic, large single crystals, massive, oriented overgrowths
Twinning	Rare contact twins on {130}
Cleavage	[100] perfect, [110] and [011] poor
Fracture	uneven to conchoidal
Mohs scale hardness	4–5
Luster	Vitreous to subresinous
Streak	White to grayish white
Diaphaneity	Transparent to translucent
Specific gravity	3.445–3.50
Optical properties	Biaxial (+), 2V = 65°
Refractive index	nα=1.669, nβ=1.673, nγ=1.682
Birefringence	δ =0.0130
Pleochroism	None to weak
References	[1][2][3]

Lithiophylite is a resinous reddish to yellowish brown mineral crystallizing in the orthorhombic system often as slender prisms. It is usually associated with lepidolite, beryl, quartz, albite, amblygonite, and spodumene of pegmatitic origin. It rather readily weathers to a variety of secondary manganese phosphates and oxides. It is a late-stage mineral in some complex granite pegmatites.[3] Members of the triphylite-lithiophilite series readily alter to secondary minerals.

The type locality is the Branchville Quarry, Branchville, Fairfield County, Connecticut where it was first reported in 1878.[2] The largest documented single crystal of lithiophilite was found in New Hampshire, US, measured 2.44×1.83×1.22 m³ and weighed ~20 tonnes.[4]

The synthetic form of triphylite, lithium iron phosphate, is a promising material for the production of lithium-ion batteries.