Triphylite is a lithium iron(II)

phosphate mineral Phosphate minerals contain the tetrahedrally coordinated phosphate (PO43−) anion along sometimes with arsenate (AsO43−) and vanadate (VO43−) substitutions, and chloride (Cl−), fluoride (F−), and hydroxide (OH−) anions that also fit ...

with the chemical formula LiFePO₄.IMA-CNMNC List of Mineral Names
(May 2015),

International Mineralogical Association Founded in 1958, the International Mineralogical Association (IMA) is an international group of 40 national societies. The goal is to promote the science of mineralogy and to standardize the nomenclature of the 5000 plus known mineral species. Th ...

It is a member of the

triphylite group Triphylite is a lithium iron(II) phosphate mineral with the chemical formula LiFePO4.IMA-CNMNC List of Miner ...

and forms a complete

solid solution A solid solution, a term popularly used for metals, is a homogenous mixture of two different kinds of atoms in solid state and have a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The wor ...

series with the lithium manganese(II) phosphate,

lithiophilite Lithiophilite is a mineral containing the element lithium. It is lithium manganese(II) phosphate with chemical formula . It occurs in pegmatites often associated with triphylite, the iron end member in a solid solution series. The mineral with in ...

. Triphylite crystallizes in the

orthorhombic crystal system In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a ...

. 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.

Etymology and history

The mineral was first discovered and examined in 1834 by German mineralogist Johann Nepomuk von Fuchs at Hennenkobel Mine in the

Bavarian Forest The village of Zell in the Bavarian Forest The Bavarian Forest ( German: ' or ''Bayerwald''; bar, Boarischa Woid) is a wooded, low-mountain region in Bavaria, Germany that is about 100 kilometres long. It runs along the Czech border and is ...

... The name derives from the Greek words ''tri'' ("three") and ''phulon'' ("family"), referring to the three cations found in natural samples of triphylite (Li⁺, Fe²⁺, Mn²⁺).

Crystal Structure

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.

Properties

Triphylite is soluble in hydrochloric and sulfuric acid. Under a blowpipe, it melts to form a dark gray, magnetic ball. Over time, the mineral undergoes alteration by oxidation, increasing the oxidation state of iron from +2 to +3 and allowing the lithium to escape, forming heterosite, FePO₄. 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 to

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers qui ...

-type silicates.

References

Lithium minerals Iron(II) minerals Phosphate minerals Orthorhombic minerals Minerals in space group 62 {{phosphate-mineral-stub