Usovite

Formula: Ba₂CaMgAl₂F₁₄

Origin of name: for Mikhail Antonovich Usov (1883-1939), Russian geologist

Crystal system: Monoclinic

Crystal class:  m or 2/m

Twinning:

Unit cell: a = 13.565, b = 5.2, c = 14.557, β = 91.35°

Colour: Brown to dark brown

Diaphaneity: Opaque to translucent in thin fragments

Luster: Vitreous to greasy

Habit: Indistinct, elongated plates to 1.5 cm, irregular grains 0.t to 3 mm

Hardness: 3.5

Specific gravity: 4.18

Cleavage: 1; perfect, another at 44 to the first noted under the microscope

Tenacity: Irregular fracture

Streak: White

Synonyms/varieties:

Comments:  Diamagnetic