Neptunite
Mineral KNa2Li(Fe,Mn)2Ti2Si8O24
About it
Black prisms with a square cross-section and red glints in thin edges, classic with blue benitoite on natrolite at California's Dallas Gem mine; also Mont Saint-Hilaire and Greenland.
- Type
- Mineral
- Group
- Silicate (phyllosilicate), neptunite group
- Formula
- KNa2Li(Fe,Mn)2Ti2Si8O24
- Hardness (Mohs)
- 5–6
- Specific gravity
- 3.19–3.23
- Streak
- reddish brown
- Lustre
- vitreous (glassy)
- Crystal system
- Monoclinic
- Colours
- black, dark red-brown in thin edges
- Transparency
- opaque
- Cleavage and fracture
- perfect in two directions
Typical values: real specimens vary. For more, see mindat.org.