How to identify Amethyst and Sodalite

To correctly identify Amethyst and Sodalite (Quartz (Amethyst variety) and 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

   Amethyst: Purple, violet, lilac. Sodalite: Rich blue, often with white streaks or patches (calcite), sometimes grey, green, or pink.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Amethyst: Vitreous (glassy). Sodalite: Vitreous to greasy.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Amethyst: Crystalline, often forming prismatic crystals or druzy coatings. Sodalite: Granular, massive, or rarely as dodecahedral crystals.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Amethyst: Hexagonal prisms terminated by rhombohedra. Sodalite: Typically massive, granular, or as dodecahedral crystals (rare).

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Amethyst: None (conchoidal fracture). Sodalite: Distinct dodecahedral cleavage (three directions at 90 degrees).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Amethyst: Hydrothermal veins, geodes, vugs in igneous (basalt, granite) and metamorphic rocks. Sodalite: Alkaline igneous rocks (nepheline syenites), pegmatites, and metasomatic contact zones.

Key Facts

Hardness

Amethyst: 7 (Mohs); Sodalite: 5.5 - 6 (Mohs)

Specific Gravity

Amethyst: 2.65; Sodalite: 2.13 - 2.29

Crystal System

Amethyst: Trigonal; Sodalite: Isometric

Color

Amethyst: Purple, violet; Sodalite: Blue, grey, green, pink

Luster

Amethyst: Vitreous; Sodalite: Vitreous to greasy

Transparency

Amethyst: Transparent to translucent; Sodalite: Transparent to opaque

Fracture

Amethyst: Conchoidal; Sodalite: Uneven to conchoidal

Cleavage

Amethyst: None; Sodalite: Distinct dodecahedral (3 directions at 90 degrees)

Composition

Amethyst: Silicon dioxide (SiO2); Sodalite: Sodium aluminum silicate chloride (Na4Al3Si3O12Cl)

Physical characteristics

• Crystal Habit: Amethyst: Prismatic, often terminated, massive, druzy. Sodalite: Massive, granular, rarely dodecahedral crystals.
• Cleavage Type: Amethyst: None. Sodalite: Distinct dodecahedral (110) in three directions at 90 degrees.
• Fracture Type: Amethyst: Conchoidal. Sodalite: Uneven to conchoidal.
• Tenacity: Amethyst: Brittle. Sodalite: Brittle.
• Luster Type: Amethyst: Vitreous. Sodalite: Vitreous to greasy.

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