Mineral - Neptunite
Neptunite
Chemical Properties
Mineral Class
Silicates
Toxicity
none
Formula
KNa₂Li(Fe²⁺)₂Ti₂Si₈O₂₄
Unit Cell
a=16.43 b=12.48 c=9.98 β=116° Z=4
Physical Properties
Hardness
5 - 6
Streak
brownredred brown
Density
Normal (2-3,5)
Cleavage
Perfect after {110}
Fracture
conchoidal
Tenacity
Brittle
Optical Properties
Color
blackbrown
Birefringence
0.045
Luster
Vitreous
Transparency
opaque
Pleochroism
Geomineralogical Properties
Crystal System
monoclinic
Point Group
monoclinic-domatic - m
Space Group
Cc (9)
Habit
prismatic, tabular
Formation
(1) Primary magmatic, as a late-stage crystallization in alkaline pegmatites and hydrothermal veins, associated with peralkaline syenites.
(2) Hydrothermal, as a fracture-filling mineral in the blue schist facies under high-pressure, low-temperature conditions, often associated with sodium-rich metasomatites and serpentinites.
Paragenesis
Twinning
Contact twin after {001}
Rarity
Rarely
Synonyms
Neptunite
Composition
Elements
Mass
SiO₂
52.29
TiO₂
17.35
FeO
11.92
MnO
2.27
MgO
1.55
CaO
0.62
Li₂O
1.63
Na₂O
6.81
K₂O
5.58
California (Dana 1895)
Groups and Members
Neptunite-Group