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 Triphylite crystal in matrix, collected from Smith Quarry (Chandler Mills Quarry),Newport, New Hampshire43°21′28″N72°15′8″W / 43.35778°N 72.25222°W /43.35778; -72.25222[1] | |
| General | |
|---|---|
| Category | Phosphate minerals |
| Formula | 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 thetriphylite group and forms a completesolid solution series with the lithium manganese(II) phosphate,lithiophilite. Triphylite crystallizes in theorthorhombic crystal system. It rarely forms prismatic crystals and is more frequently found inhypidiomorphic rock. It is bluish- to greenish-gray in color, but uponalteration becomes brown to black.
The mineral was first discovered and examined in 1834 by German mineralogistJohann Nepomuk von Fuchs atHennenkobel Mine in theBavarian Forest.[7][8] The name derives from the Greek wordstri ("three") andphulon ("family"), referring to the three cations found in natural samples of triphylite (Li+, Fe2+, Mn2+).[5]
Triphylite crystallizes in an orthorhombic crystal system. The lithium coordinates to six oxygen atoms in a distorted octahedron. Likewise, the iron centers are octahedrally coordinated. The structure contains isolated phosphate tetrahedra.[9]
Triphylite is soluble inhydrochloric andsulfuric acid. Under ablowpipe, it melts to form a dark gray, magnetic ball.[7] Over time, the mineral undergoes alteration by oxidation, increasing the oxidation state of iron from +2 to +3 and allowing the lithium to escape, formingheterosite, FePO4.[8]
Triphylite forms a complex solution series with lithiophilite, LiMnPO4, so that natural sources of triphylite usually contain manganese. The structures of members within this series are similar toolivine-type silicates.[10]
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