Ludlamite

Ludlamite
General
Category	Phosphate mineral
Formula	(Fe,Mn,Mg)3(PO4)2·4H2O
IMA symbol	Lud1
Strunz classification	8.CD.20
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/a
Unit cell	a = 10.541(5), b = 4.646(4) c = 9.324(5) [Å]; β = 100.52°; Z = 2
Identification
Color	Apple-green to bright green
Crystal habit	Tabular crystals; massive, granular
Cleavage	Cleavage: perfect on {001}, indistinct on {100}
Mohs scale hardness	3.5
Luster	Vitreous, pearly on cleavage
Streak	Pale greenish white
Diaphaneity	Translucent
Specific gravity	3.12–3.19
Optical properties	Biaxial (+)
Refractive index	nα = 1.650 - 1.653 nβ = 1.669 - 1.675 nγ = 1.688 - 1.697
Birefringence	δ = 0.038 - 0.044
2V angle	Measured: 82°
References	234

Ludlamite is a rare phosphate mineral with chemical formula (Fe,Mn,Mg)₃(PO₄)₂·4H₂O. It was first described in 1877 for an occurrence in Wheal Jane mine in Cornwall, England and named for English mineralogist Henry Ludlam (1824–1880).

It occurs in granite pegmatites and as a hydrothermal alteration product of earlier phosphate bearing minerals in a reducing environment.⁴ It occurs associated with whitlockite, vivianite, triploidite, triplite, triphylite, siderite, phosphoferrite, fairfieldite and apatite.²