Benitoite with Neptunite and Natrolite

Benitoite
Barium Titanium Silicate, BaTiSi3O9
Crystal System: Trigonal
Hardness: 6.2-6.5
Density: 3.65

Benitoite occurs as stubby, prismatic, dipyramidal crystals in various shades of translucent to transparent blue with a vitreous to subadamantine luster. It exhibits pleochroism; a crystal appears blue when viewed through the acute faces and colorless when viewed through the obtuse faces of a crystal. Benitoite fluoresces in ultraviolet light. It is associated with neptunite, natrolite, crossite and albite.

Neptunite
Sodium Potassium Iron Titanium Silicate, Na2KLi(Fe,Mn)2Ti2Si8O24
Crystal System: Monoclinic
Hardness: 5.0-6.0
Density: 3.23

Neptunite occurs in nepheline syenites and in cavities in nepheline pegmatites. It is associated with benitoite and natrolite. Neptunite exhibits elongated, prismatic, black to dark brown crystals which may be opaque or translucent.

Natrolite
Sodium Aluminum Silicate Hydrate, Na2Al2Si3O10.2H2O
Crystal System: Orthorhombic
Hardness: 5.0-5.5
Density: 2.20-2.26

Natrolite is a member of the zeolite group. It occurs as slender, prismatic crystals with vertical striations, usually as globular aggregates of fibrous, radiating needles. It ranges in color from white, pink, or yellowish to transparent. It is found lining cavities in basalts and other lavas and is associated with calcite and zeolites. Natrolite sometimes fluoresces orange in ultraviolet light.


Rocks from Martin Friedlander's Collection

Index of Specimen Images

Table of Contents

bkeller@rockhounds.com 8/8/95