Nordite

Formula: (Ce,La)(Sr,Ca)Na₂(Na,Mn)(Zn,Mg)Si₆O₁₇

Origin of name: from Russian for north

Crystal system: orthorhombic

Crystal class: 2/m 2/m 2/m

Twinning: 

Unit cell: 

Colour: light brown to dark brown

Diaphaneity: translucent

Luster: vitreous, greasy on fracture

Habit: crystals tabular, to 1 cm, curved and lamellar in radial-fibrous aggregates

Hardness: 5

Specific gravity: 3.43 to 3.49

Cleavage: 1; {100} distinct

Tenacity: 

Streak: white

Synonyms/varieties:

Comments: two distinct species with the extensions -(Ce) and -(La) indicating the predominant rare earth cation in the formula