Radiating
fibrous crystals of Natrolite in a basalt vug from the Horseshoe Dam area of
Arizona.
This close up view shows the delicate fibrous crystals of Natrolite radiating
outward from its point of origin on the wall of the basalt vug. Note the
zoning of the radiating mass exposed in the broken cluster on the bottom of the
photo.
Another cluster of Natrolite in a vug
of basalt showing concentric zoning. Locality is Horseshoe Dam, AZ.
CHEMISTRY Na2Al2Si3O10 .2H2O
CRYSTALLOGRAPHY Orthorhombic (pseudo tetragonal)
CRYSTAL GROWTH AND HABITS Natrolite crystals are normally long prismatic or sometimes tabular. They are usually in divergent groups or radiating fibrous masses. Natrolite can also be granular or massive.
COLOR AND OTHER OPTICAL PROPERTIES Natrolite can be colorless, white, gray and even bluish to yellowish or pink. It is transparent to translucent.
HARDNESS 5 - 5.5
SPECIFIC GRAVITY 2.2
LUSTER Vitreous to pearly
STREAK White
BREAKABILITY Good prismatic cleavage, brittle
OCCURRENCE Natrolite is a zeolite that forms in vugs or cavities in basaltic rocks.
ASSOCIATED MINERALS Other Zeolites, Calcite, Nepheline, Sodalite, Quartz