Strengite

Strengite is a relatively rare iron phosphate mineral with the formula: FePO₄·2H₂O.^[5] The mineral is named after the German mineralogist Johann August Streng [de] (1830–1897).^[6] Lavender, pink or purple in hue, it is similar to variscite^[7] and is partially soluble, particularly in conditions where there is a low pH and low oxidation-reduction potential.^[5] The color comes from ferric ion (Fe³⁺).^[8]

Strengite
A small crystal of Strengite
General
Category	Minerals
Formula	FePO4·2H2O
IMA symbol	Stg[1]
Strunz classification	8.CD.10
Dana classification	40.04.01.02
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M Symbol: (2/m 2/m 2/m)
Space group	Pcab
Identification
Formula mass	186.85 g/mol
Color	Colorless, pale violet, deep violet, red, carmine red, greenish white
Crystal habit	Botryoidal, radial, spherical
Cleavage	{010} Good, {001} Poor
Mohs scale hardness	3.5–4
Luster	Vitreous
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	2.84
Density	2.87 g/cm3
Optical properties	Biaxial (+)
2V angle	72° – 88°
Dispersion	r < v, relatively strong
References	[2][3][4]