How to identify Sodalite

To correctly identify Sodalite (Sodalite), 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 a rich, royal blue to violet-blue, but can also be gray, green, yellow, or pink (hackmanite). Often exhibits white streaks or veins.

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 or cubic.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Typically massive or granular. When euhedral, it forms dodecahedral or cubic crystals, though these are uncommon.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Distinct dodecahedral cleavage in three directions (110), but often difficult to observe in massive material.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in silica-undersaturated, alkali-rich igneous rocks such as nepheline syenites, phonolites, and related pegmatites. Also occurs in metasomatic deposits.

Key Facts

Hardness

5.5-6 on the Mohs scale

Specific Gravity

2.13-2.33 g/cm³

Crystal System

Cubic (isometric)

Color

Blue, gray, green, yellow, pink (hackmanite)

Luster

Vitreous to greasy

Transparency

Transparent to translucent to opaque

Fracture

Conchoidal to uneven

Cleavage

Distinct dodecahedral (110) in three directions

Composition

Sodium aluminum silicate with chloride: Na8(Al6Si6O24)Cl2

Physical characteristics

• Crystal Habit: Massive, granular, disseminated grains; rarely euhedral dodecahedral or cubic crystals.
• Cleavage Type: Distinct dodecahedral (110) in three directions, often imperfect or difficult to observe in massive material.
• Fracture Type: Conchoidal to uneven.
• Tenacity: Brittle.
• Luster Type: Vitreous to greasy.

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