How to identify Tourmalinated Quartz

To correctly identify Tourmalinated Quartz (Quartz (SiO2) with Tourmaline (complex borosilicate)), 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

   Clear, milky, or smoky quartz with black (most common), dark green, or rarely other colored needle-like or prismatic tourmaline inclusions.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) for both quartz and tourmaline.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth to conchoidal fracture surfaces for quartz; tourmaline inclusions are typically smooth and prismatic.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz typically forms hexagonal prisms with pyramidal terminations; tourmaline forms elongated prismatic crystals, often with characteristic triangular cross-sections, embedded within the quartz.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz has no true cleavage, exhibiting conchoidal fracture. Tourmaline has poor to indistinct cleavage, often appearing as brittle fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Granitic pegmatites, hydrothermal veins, and granitic intrusions. It is often found in association with other pegmatitic minerals.

Key Facts

Hardness

Quartz: 7 on Mohs scale. Tourmaline: 7-7.5 on Mohs scale. The aggregate will generally be around 7.

Specific Gravity

Quartz: 2.65 g/cm³. Tourmaline: 3.0-3.26 g/cm³. The aggregate will be slightly higher than pure quartz, typically around 2.65-2.75 g/cm³.

Crystal System

Quartz: Trigonal. Tourmaline: Trigonal.

Color

Colorless, white, or smoky quartz with black, dark green, or rarely other colored tourmaline inclusions.

Luster

Vitreous.

Transparency

Transparent to translucent.

Fracture

Conchoidal (quartz); uneven to conchoidal (tourmaline).

Cleavage

None (quartz); poor to indistinct (tourmaline).

Composition

Silicon dioxide (SiO2) for quartz, and a complex borosilicate for tourmaline, with general formula XY3Z6(T6O18)(BO3)3V3W, where X, Y, Z, T, V, W represent various cations and anions.

Physical characteristics

• Crystal Habit: Quartz typically forms prismatic crystals; tourmaline forms acicular to prismatic crystals embedded within the quartz.
• Cleavage Type: Quartz: None. Tourmaline: Poor to indistinct on {1011} and {0001}.
• Fracture Type: Conchoidal (quartz); uneven to conchoidal (tourmaline).
• Tenacity: Brittle.
• Luster Type: Vitreous.

Explore Tourmalinated Quartz