How to identify Sodalite

To correctly identify Sodalite (Na8(Al6Si6O24)Cl2), 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 royal blue, but can also be gray, green, yellow, pink, or white. Often mottled with white streaks or patches of calcite.

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 within host rock. Crystals are rare but can be dodecahedral.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Cubic system, typically forming dodecahedra, but more commonly found as massive aggregates or disseminated grains.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Poor to distinct in three directions (dodecahedral), but often difficult to observe in massive material.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in silica-undersaturated igneous rocks (e.g., nepheline syenites, phonolites) and associated metasomatic rocks (e.g., fenites). It is an indicator mineral for alkaline igneous activity.

Key Facts

Hardness

5.5-6 (Mohs scale)

Specific Gravity

2.13-2.29 g/cm³

Crystal System

Cubic

Color

Deep royal blue (most common), also gray, green, yellow, pink, white

Luster

Vitreous to greasy

Transparency

Transparent to opaque

Fracture

Conchoidal to uneven

Cleavage

Poor to distinct dodecahedral {110}

Composition

Sodium aluminum silicate with chlorine

Physical characteristics

• Crystal Habit: Massive, granular, disseminated grains; rarely as dodecahedral crystals
• Cleavage Type: Poor to distinct dodecahedral {110}
• Fracture Type: Conchoidal to uneven
• Tenacity: Brittle
• Luster Type: Vitreous to greasy

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