Neptunite

Formula: KNa₂Li(Fe,Mn)₂Ti₂Si₈O₂₄

Origin of name: from Neptune, Roman god of the sea

Crystal system: monoclinic

Crystal class: m

Twinning: on {301} penetration

Unit cell: a = 16.46 Å, b = 12.50 Å, c = 10.01 Å, b = 115.4°

Colour: reddish-black

Diaphaneity: 

Luster: vitreous

Habit: crystals prismatic, square cross section

Hardness: 5 to 6

Specific gravity: 3.19 to 3.23

Cleavage: 1; {110} perfect

Tenacity: conchoidal, brittle

Streak: cinnamon brown

Synonyms/varieties:

Comments: series with mangan-neptunite