Arseniosiderite

Formula:  Ca₂Fe₃(AsO₄)₃O₂^.3H₂O

Origin of name:  From composition arsenic and  the Greek word sideros for iron

Crystal system:  Monoclinic, pseudo-tetragonal

Crystal class:  2/m

Twinning:

Unit cell:   a = 17.76 Å, b = 19.53 Å, c = 11.30 Å, b = 96.0°

Colour:  Yellow to dark brown

Diaphaneity: Opaque, translucent through thin edges

Luster:  Submetallic to silky

Habit:  Massive radial-fibrous aggregates, felted to aggregates, euhedral crystals very rare

Hardness:  4.5

Specific gravity:  3.58 to 3.60

Cleavage:  1; {001} perfect

Tenacity:

Streak:  Ochre-yellow

Synonyms/varieties:

Comments: Found as a rare secondary mineral formed by the oxidation of earlier arsenic-bearing minerals, typically scorodite or arsenopyrite.