Brannockite

Formula:  KSn₂Li₃Si₁₂O₃₀

Origin of name:  For Kent Combs Brannock (1923-1973), American chemist and mineral collector, Kingsport, Tennessee, U.S.A.

Crystal system:  Hexagonal

Crystal class:  6/m 2/m 2/m

Twinning:  Universal about axis perpendicular to [0001]

Unit cell: a = 10.002 Ǻ, c = 14.263 Ǻ

Colour:  Colourless

Diaphaneity: Semitransparent

Luster:  Vitreous

Habit:  Crystals microscopic thin plates

Hardness:

Specific gravity:  2.980

Cleavage:  None

Tenacity:  Brittle

Streak:

Synonyms/varieties:

Comments:  Fluoresces bright blue-white under SW-UV. Member of the milarite group. Found in late hydrothermal portions of Li-Sn-rich pegmatite, in vugs and on flat fracture surfaces.