Pectolite

Formula: NaCa₂Si₃O₈(OH)

Origin of name: from Greek for compact

Crystal system: triclinic

Crystal class: -1

Twinning: 

Unit cell: a = 8.00 Å, b = 7.03 Å, c = 7.03 Å, a = 90.5°, b = 95.2°, g = 102.5°

Colour: colourless, white

Diaphaneity: 

Luster: vitreous or silky

Habit: crystals tabular or acicular, elongated along b-axis, in radiating aggregates, globular

Hardness: 4.5 to 5

Specific gravity: 2.74 to 2.88

Cleavage: 2; {001} and {100} perfect

Tenacity: brittle

Streak: 

Synonyms/varieties: schizolite (Mn-rich variety)

Comments: series with serandite