Strengite

Formula: FePO₄.2H₂O

Origin of name: for J. Streng, German mineralogist

Crystal system: orthorhombic

Crystal class: 2/m 2/m 2/m

Twinning: uncommon on {201}

Unit cell: a = 10.12 Å, b = 9.886 Å, c = 8.723 Å

Colour: colourless, pale to deep violet, red

Diaphaneity: 

Luster: vitreous

Habit: crystals pseudo-octahedral, tabular, stout prismatic, spherical aggregates, crusts

Hardness: 3.5 to 4.5

Specific gravity: 2.87

Cleavage: 2; {010} good, {001} poor

Tenacity: conchoidal, brittle

Streak: white

Synonyms/varieties: barrandite (Al-rich variety)

Comments: dimorphous with phosphosiderite, series with variscite