igneous
Blue-gray feldspar-rich rock, likely sodalite-bearing syenite
Sodalite-bearing nepheline syenite; sodalite Na₈(Al₆Si₆O₂₄)Cl₂, with feldspar and minor dark minerals
AI-generated identification · may be incorrectHardness about 5.5–6 (sodalite) and 6–6.5 (feldspar); coarse-grained, blue-gray with white mineral patches and dull to glassy luster. Crystals are interlocking, with feldspar cleavage; exact identification requires testing.
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Physical properties
Hardness about 5.5–6 (sodalite) and 6–6.5 (feldspar); coarse-grained, blue-gray with white mineral patches and dull to glassy luster. Crystals are interlocking, with feldspar cleavage; exact identification requires testing.
Formation & geological history
Likely formed by slow cooling of an alkaline, silica-poor magma, producing coarse crystals; typically Mesozoic to Precambrian in age depending on locality. Common in alkaline igneous complexes.
Uses & applications
Used primarily as a decorative stone, lapidary material, and collector specimen; sodalite-rich varieties may be polished for ornaments and jewelry. Not generally a major construction stone in small specimens.
Geological facts
The blue color commonly comes from sodalite, while white patches are usually nepheline or feldspar; dark grains may be aegirine or amphibole. Lazurite-rich rock can look similar but commonly has pyrite flecks.
Field identification & locations
Look for a blue-gray coarse texture, white feldspar/nepheline patches, and no obvious glassy conchoidal fracture; a streak, hardness, and acid test help distinguish it from lapis lazuli and slag. Occurs in Canada, Brazil, Russia, Greenland, and other alkaline complexes.
