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NATROLITE:

PHYSICAL CHARACTERISTICS:

Color is clear or white; also tinted yellow and brown.

Luster is vitreous to dull on some compact masses.

Transparency: crystals are transparent to translucent.

Crystal System is orthorhombic; mm2

Crystal Habits include sprays of needle thin acicular crystals with a pyramidal termination. Also nodules, fiberous and massive crusts.

Cleavage is perfect in two directions, prismatic. Cleavage is rarely seen due to small crystal size.

Fracture is conchoidal.

Hardness is 5 - 5.5.

Specific Gravity is approximately 2.2 (very light)

Streak is white

. Associated Minerals are quartz, apophyllite, benitoite, heulandite, stilbite and other zeolites.

Notable Occurrences include Poona, India; San Benito, California; New Jersey and Nova Scotia.

Best Field Indicators are crystal habit, density and associations.

Natrolite is a common and popular zeolite mineral. Its radiating sprays of ice clear acicular crystals are not exclusive to natrolite but they are a hallmark of this mineral. Natrolite can make a fine specimen in itself but it often is an accessory to other minerals and can enhance the beauty of associated minerals such as apophyllite, heulandite, benitoite and others.

Natrolite's structure has a typical zeolite openness about it that allows large ions and molecules to reside and actually move around inside the overall framework. The structure contains open channels that allow water and large ions to travel into and out of the crystal structure. The size of these channels controls the size of the molecules or ions, and therefore zeolites like natrolite can act as a chemical sieve. Natrolite's structure contains chains of silicate tetrahedrons aligned in one direction; this produces the needle-like crystals. Its cleavage results from the weaker bonds between the chains.

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