How to identify Sodalite

To correctly identify Sodalite (Na4Al3Si3O12Cl), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   Typically deep blue, often with white streaks or patches of calcite. Can also be grey, green, pink, or white.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to greasy.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Massive, granular, or as disseminated grains. Crystals are rare but can be dodecahedral.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Isometric system, typically dodecahedral crystals, but more commonly found in massive or granular aggregates.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Poor to distinct on {110}.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Alkaline igneous rocks (nepheline syenites, phonolites), metasomatic rocks, and contact metamorphic limestones.

Key Facts

Hardness

5.5-6 on the Mohs scale.

Specific Gravity

2.13-2.30 g/cm³.

Crystal System

Isometric (Cubic).

Color

Typically deep blue, but can be grey, green, pink, or white. Often mottled with white calcite.

Luster

Vitreous to greasy.

Transparency

Transparent to opaque.

Fracture

Conchoidal to uneven.

Cleavage

Poor to distinct on {110} (dodecahedral).

Composition

Sodium aluminum silicate with chloride.

Physical characteristics

• Crystal Habit: Massive, granular, disseminated grains; rarely as dodecahedral crystals.
• Cleavage Type: Poor to distinct dodecahedral.
• Fracture Type: Conchoidal to uneven.
• Tenacity: Brittle.
• Luster Type: Vitreous to greasy.

Explore Sodalite