Ludlamite

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).

Ludlamite
General
Category	Phosphate mineral
Formula	(Fe,Mn,Mg)3(PO4)2·4H2O
IMA symbol	Lud[1]
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	[2][3][4]

Occurrence

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]