Tainiolite

Formula: KLiMg₂Si₄O₁₀F₂

Origin of name: from Greek for band or strip, in allusion to the tabular habit of the crystals

Crystal system: Monoclinic

Crystal class: 2/m

Twinning: Penetration trillings rare

Unit cell: a = 5.231, b = 9.065, c = 10.14, β = 99.86°

Colour: Brownish, colourless, greenish brown, typically concentrically zones

Diaphaneity: Transparent

Luster: Vitreous, silky

Habit: Crystal tabular, micaceous, pseudohexagonal, to 3.5 cm, scales, cryptocrystalline aggregates

Hardness: 2.5 to 3

Specific gravity: 2.82 to 2.90

Cleavage: 1; {001} perfect, micaceous

Tenacity: Flexible foliae, somewhat elastic

Streak: White

Synonyms/varieties: taeniolite

Comments: member of mica group, -1M and -2M polytypes are known, fluorescent