Atelestite

Formula:  Bi₂O(AsO₄)(OH)

Origin of name:  Probably from the Greek word ateles = imperfect or incomplete, as the composition was undetermined when the mineral was first described

Crystal system:  Monoclinic

Crystal class:  2/m

Twinning:

Unit cell: a = 10.831 Å, b = 7.430 Å, c = 7.000 Å, b = 107.08°

Colour:  Bright yellow to yellowish green or wax-yellow

Diaphaneity: Transparent to translucent

Luster:  Resinous to adamantine

Habit:  Crystals minute tabular to prismatic; mammillary or spherical crystalline aggregates

Hardness:  4.5 to 5

Specific gravity:  7.14

Cleavage:  1; {100} indistinct

Tenacity:

Streak: White

Synonyms/varieties:

Comments: Found as a rare secondary mineral in the oxidised zone of bismuth- and arsenic-bearing mineral deposits.