Triploidite is an uncommon manganese

Manganese

Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...

 iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 phosphate mineral with formula

Chemical formula

A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

: . It crystallizes in the monoclinic crystal system

Crystal system

In crystallography, the terms crystal system, crystal family, and lattice system each refer to one of several classes of space groups, lattices, point groups, or crystals...

 and typically occurs as elongated and striated slender prisms which may be columnar to fibrous. Its crystals may be pinkish to yellowish brown or red-orange.

It was first described in 1878 for an occurrence in the Branchville Quarry, Branchville

Branchville, Connecticut

Branchville is a section of the southeast corner of the Town of Ridgefield, Connecticut, and is also the name of a Metro North railroad station .- History :...

, Fairfield County, Connecticut. The name is derived from its resemblance to triplite

Triplite

Triplite is a rare phosphate mineral with formula: . 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. The name is from the Greek triplos for triple, in reference to...

.

It typically occurs as hydrothermal alteration of primary phosphate minerals in granite

Granite

Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...

 pegmatite

Pegmatite

A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....

s. It occurs with triplite

Triplite

Triplite is a rare phosphate mineral with formula: . 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. The name is from the Greek triplos for triple, in reference to...

, lithiophilite

Lithiophilite

Lithiophilite is a mineral containing the element lithium. It is lithium manganese phosphate with formula: LiMnPO4. It occurs in pegmatites often associated with triphylite, the iron end member in a solid solution series...

, triphylite, eosphorite

Eosphorite

Eosphorite is a pink manganese phosphate mineral with chemical formula: MnAl2·H2O.Eosphorite crystallizes in the monoclinic crystal system. It forms prismatic crystals which often form radiating or spherical clusters...

, dickinsonite and rhodochrosite

Rhodochrosite

Rhodochrosite is a manganese carbonate mineral with chemical composition MnCO3. In its pure form, it is typically a rose-red color, but impure specimens can be shades of pink to pale brown. The streak is white. Its Mohs hardness varies between 3.5 and 4. Its specific gravity is 3.5 to 3.7. It...

.

It forms a solid solution

Solid solution

A solid solution is a solid-state solution of one or more solutes in a solvent. Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase...

 series with the iron rich wolfeite.