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PHYSICAL PROPERTIES:
Chemistry: Na4Al3(SiO4)3Cl,
Composition: Sodium Aluminum Silicate Chloride
Color: blue, white, gray, green, pink
Class: Silicates
Subclass: Tectosilicates
Group: Sodalite and feldspathoid
Crystal system: Isometric; bar 4 3/m
Crystal habit: Dodecahedral crystals
have been found, usually massive as
a rock forming mineral.
Fracture: uneven
Hardness: 5.5 - 6.0
Specific gravity: 2.1 - 2.3
Refractive Index: 1.483-1.487
Pleochroism: none
Luster: vitreous or greasy
Streak: white
Clevage: poor
Transparency: Crystals are transparent to translucent, massive specimens are opaque.
Associated Minerals: calcite, nepheline, cancrinite and other feldspathoids

COMPOSITION:
Sodium aluminum silicate with chlorine (25.6% Na20, 31.6% A1203, 37.2% Si02). 7.~% CI replaces some of the 0. Hackmanite contains sulphur in place of chlorine.

ENVIRONMENT:
A mineral of alkaline igneous and plutonic rocks. Sodalite is a member of the feldspathoid group of minerals. Minerals whose chemistries are close to that of the alkali feldspars but are poor in silica.

CRYSTAL DESCRIPTION:
Crystals small, in cavities in rock, usually in dodecahedrons. Usually massive, commonly in considerable concentrations.

DISTINGUISHING CHARACTERISTICS:
The color of blue is very typical and likely to be confused only with lapis and lazurite Blue grains in rock may not originally be fluorescent, but the pink variety, hackmanite, is brilliantly fluorescent and reversibly sensitive to light, fading to white in daylight and re- verting to pink on exposure to ultraviolet light.

USES:
It is used for s and some jewelry pieces. Sodalite is well known in the semi-precious stone trade. It is also used for carving, mineral specimens and ornamental stone. Mineral specimens are scarce.

LOCALITIES:
Rich blue masses are found near Bancroft, Ontario, and nearby along the York River there
are several massive oc- currences of hackmanite. Thinner veins of blue sodalite are found
in nepheline rocks on the Ice River, British Columbia. Litchfield, Maine, yields sodalite in smaller masses of moderate richness. Colorless crystals are found in the altered limestone blocks thrown out by the eruptions of Vesuvius. Brazil seems to be todays major producer.

TESTS:
Frequently fluorescent yellow to orange, in long- wave ultraviolet. It is the only feldspathoid
to give a positive chlorine test when dissolved in a HNO2 dilute solution. When heated it soon loses color and eventually fuses to a white glass with yellow flame coloration, After being
fired, heated specimen fluoresces brilliant orange in long-wave ultraviolet, and the fused
area fluoresces blue in short-wave ultraviolet.

FACTS & HISTORY
Sodalite is named in reference to its sodium content.

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