Umbite

Formula: K₂ZrSi₃O₉.H₂O

Origin of name: after locality Lake Umbozero (Umba), Kola Peninsula, Russia

Crystal system: Orthorhombic

Crystal class: 222

Twinning:

Unit cell: a = 10.208, b = 13.241, c = 7.174

Colour: Colourless to yellowish white

Diaphaneity: Transparent to semitransparent

Luster: Vitreous

Habit: Crystals platy

Hardness: 4.5

Specific gravity: 2.79

Cleavage: 2; {010} perfect, micaceous, {100} good

Tenacity: 

Streak: White

Synonyms/varieties:

Comments: dimorphous with kostylevite