Terskite

Formula: Na₄ZrSi₆O₁₅(OH)₂.H₂O

Origin of name: after locality Tersk shore of the Kola Peninsula, Russia

Crystal system: Orthorhombic, pseudotetragonal

Crystal class: mm2

Twinning:

Unit cell: a = 14.195, b = 14.75, c = 7.511

Colour: Colourless to pale lilac

Diaphaneity: Translucent

Luster: Vitreous

Habit: plates 1 to 3.5 mm

Hardness: 5

Specific gravity: 2.71

Cleavage: None

Tenacity: 

Streak: White

Synonyms/varieties:

Comments:  Fluorescent bright green or very pale yellow under SW-UV