Sodalite
Na₈(AlSiO₄)₆Cl₂ · Cubic
Sodalite is the affordable blue ornamental stone, widely sold in place of lapis lazuli. It is lighter, more uniformly blue, and lacks lapis's pyrite sparkle. The orange fluorescence is a striking confirmation when a UV lamp is available.
Properties
- Mohs hardness
- 5.5–6
- Streak
- white
- Lustre
- vitreous, greasy
- Colour
- Royal blue, usually mottled with white calcite veining.
- Cleavage
- Poor dodecahedral cleavage.
- Fracture
- Conchoidal to uneven
- Specific gravity
- 2.27–2.33 (water = 1)
- Magnetism
- Not magnetic
- Acid test
- No reaction
- UV
- Some specimens fluoresce
Tests that confirm sodalite
- Distinctly light in the hand for a blue stone — noticeably lighter than lapis lazuli.
- Often fluoresces bright orange under long-wave ultraviolet light.
- Lacks the golden pyrite flecks that characterise good lapis.
What sodalite gets confused with
Each of these is settled by one test. Run that test first.
Lapis lazuli
Lapis is heavier, deeper blue, and almost always carries brassy pyrite specks.
Azurite is softer, fizzes in acid, and leaves a light blue streak.
Where it is found
Alkaline igneous rocks; major sources in Brazil, Canada, and Namibia.
Is it worth anything?
Inexpensive and widely available as tumbled stones and carvings.