How to identify Dumortierite

To correctly identify Dumortierite (Dumortierite), 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, violet-blue, reddish-brown, or pink. The blue and violet hues are most characteristic.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to dull, sometimes silky in fibrous varieties.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Often fibrous, columnar, or massive. Can be granular or compact.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Usually occurs as aggregates of prismatic or fibrous crystals, often radiating or parallel. Individual crystals are rare and typically small, forming elongated prisms.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Distinct on {100}, but rarely observed due to its fibrous habit and common occurrence in massive forms.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Metamorphic rocks (gneisses, schists, quartzites), pegmatites, aplites, and hydrothermal veins, particularly in aluminum-rich and boron-bearing environments.

Key Facts

Hardness

7-8 on the Mohs scale

Specific Gravity

3.26-3.41

Crystal System

Orthorhombic

Color

Blue, violet-blue, reddish-brown, pink

Luster

Vitreous to dull, silky

Transparency

Transparent to opaque

Fracture

Uneven to splintery

Cleavage

Distinct on {100}, but rarely observed

Composition

Al7(BO3)(SiO4)3O3

Physical characteristics

• Crystal Habit: Prismatic, fibrous, columnar, radiating aggregates, massive
• Cleavage Type: Distinct on {100}, but often obscured by fibrous habit
• Fracture Type: Uneven to splintery
• Tenacity: Brittle
• Luster Type: Vitreous to dull, silky

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