Phosphosiderite

Phosphosiderite is a rare mineral named for its main components, phosphate and iron. The siderite at the end of phosphosiderite comes from the word "sideros", the Greek word for iron. It was published in 1890, and has been a valid species since pre-IMA. It is an IMA approved mineral which got grandfathered, meaning its name is still believed to refer to an existing species.

Phosphosiderite
Red phosphosiderite between violet strengite. Picture width 4 mm.
General
CategoryPhosphate minerals
Formula
(repeating unit)		Hydrated iron phosphate FePO4·2H2O
IMA symbolPhsd
Crystal systemMonoclinic
Crystal classPrismatic 2/m
Space groupP21/n (no. 14)
Unit cell454.76 ų
Identification
Formula mass186.85
ColorUsually red to pink to purple, sometimes green, usually yellow veined
Crystal habitTabular {010} or stout prismatic [001]
TwinningCommon on {101}, typically as interpenetration
Cleavage{010} Distinct, {001} Indistinct
FractureUneven
Mohs scale hardness3.5–4
LusterVitreous
StreakWhite
DiaphaneityTransparent, translucent
Specific gravity2.74–2.76
Density2.74 – 2.76 measured, 2.76 calculated
Optical propertiesBiaxial (−)
Refractive indexnα = 1.692
nβ = 1.725
nγ = 1.738
Birefringence0.046
PleochroismVisible
2V angleMeasured: 62°, Calculated: 62°
DispersionVery strong
r > v
SolubilityTotally soluble in hydrochloric acid, nearly insoluble in nitric acid
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