How to identify Tourmalinated Quartz

To correctly identify Tourmalinated Quartz (SiO2 (Quartz) with (Na,Ca)(Li,Mg,Fe,Mn,Al)3Al6(BO3)3Si6O18(OH)4 (Tourmaline Group)), 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 be dark green, brown, or rarely other colors.

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

   Crystalline, with distinct acicular or prismatic tourmaline crystals embedded within a larger quartz crystal.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz typically forms hexagonal prisms with pyramidal terminations. Tourmaline forms trigonal prisms, often with striations parallel to the c-axis, embedded within the quartz.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz: None. Tourmaline: Poor basal cleavage, often not observable in inclusions.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Granitic pegmatites, hydrothermal veins, and some metamorphic rocks.

Key Facts

Hardness

Quartz: 7 on Mohs scale. Tourmaline: 7-7.5 on Mohs scale.

Specific Gravity

Quartz: 2.65 g/cm³. Tourmaline: 3.0-3.26 g/cm³ (varies with composition).

Crystal System

Quartz: Trigonal. Tourmaline: Trigonal.

Color

Colorless, white, or smoky quartz with black, dark green, or brown tourmaline inclusions.

Luster

Vitreous.

Transparency

Transparent to translucent (quartz), opaque to translucent (tourmaline inclusions).

Fracture

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

Cleavage

Quartz: None. Tourmaline: Poor basal cleavage, often not observed.

Composition

SiO2 (Quartz) with complex borosilicate (Tourmaline Group).

Physical characteristics

• Crystal Habit: Quartz typically forms prismatic crystals with hexagonal cross-sections and pyramidal terminations. Tourmaline inclusions are acicular to prismatic, often with characteristic triangular cross-sections and vertical striations.
• Cleavage Type: Quartz: Absent. Tourmaline: Imperfect to poor on {1011} and {0001}.
• Fracture Type: Conchoidal in quartz, uneven to conchoidal in tourmaline.
• Tenacity: Brittle for both minerals.
• Luster Type: Vitreous (glassy).

Explore Tourmalinated Quartz