How to identify Tourmalinated Quartz

To correctly identify Tourmalinated Quartz (SiO2 (Quartz) with (Na,Ca)(Mg,Fe)3Al6(BO3)3Si6O18(OH)4 (Tourmaline)), 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

   Quartz matrix can be colorless, white, smoky, or rarely other hues. Tourmaline inclusions are typically black (schorl), but can also be green, pink, or blue depending on the tourmaline species.

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 slightly uneven fracture surface for quartz; tourmaline inclusions are typically prismatic or acicular, feeling smooth within the quartz.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz typically forms hexagonal prisms with pyramidal terminations, though it can be massive. Tourmaline forms characteristic trigonal prisms with striations parallel to the c-axis, often appearing as needles or slender columns 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 parallel to the prism faces.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Pegmatites, hydrothermal veins, and regionally metamorphosed rocks, particularly those associated with granitic intrusions.

Key Facts

Hardness

Quartz: 7 (Mohs); Tourmaline: 7-7.5 (Mohs). The aggregate will scratch glass.

Specific Gravity

Quartz: 2.65 g/cm³; Tourmaline: 3.0-3.26 g/cm³. The aggregate will have a specific gravity slightly higher than pure quartz.

Crystal System

Quartz: Trigonal; Tourmaline: Trigonal.

Color

Colorless, white, or smoky quartz with black, green, pink, or blue tourmaline inclusions.

Luster

Vitreous.

Transparency

Transparent to translucent (quartz); Opaque to translucent (tourmaline inclusions).

Fracture

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

Cleavage

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

Composition

Silicon dioxide (SiO2) for quartz, with complex borosilicate (Na,Ca)(Mg,Fe)3Al6(BO3)3Si6O18(OH)4 for tourmaline.

Physical characteristics

• Crystal Habit: Quartz: Prismatic, massive, granular; Tourmaline: Prismatic, acicular, columnar, often with triangular cross-section and striations.
• Cleavage Type: Quartz: None; Tourmaline: Poor to indistinct on {1011} and {1120}.
• Fracture Type: Quartz: Conchoidal; Tourmaline: Uneven to conchoidal.
• Tenacity: Brittle for both minerals.
• Luster Type: Vitreous.

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