How to identify Tourmalinated Quartz

To correctly identify Tourmalinated Quartz (SiO2 with (Na,Ca)(Mg,Fe)3Al6(BO3)3Si6O18(OH)4), 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 is typically colorless, white, or smoky. Tourmaline inclusions are most commonly black (schorl), but can also be dark green, blue, or brown.

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 rough depending on the crystal faces present. The tourmaline inclusions will feel harder than the surrounding quartz if exposed.

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 rounded triangular cross-sections and striations parallel to the c-axis.

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 c-axis.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Granitic pegmatites, hydrothermal veins, and regionally metamorphosed rocks, particularly those associated with boron-rich fluids.

Key Facts

Hardness

7 (Mohs scale for quartz), 7-7.5 (Mohs scale for tourmaline)

Specific Gravity

2.65 g/cm³ (quartz), 3.0-3.2 g/cm³ (tourmaline, varies with composition)

Crystal System

Trigonal (quartz), Trigonal (tourmaline)

Color

Colorless, white, or smoky (quartz) with black, dark green, or dark blue (tourmaline) inclusions.

Luster

Vitreous

Transparency

Transparent to translucent (quartz), Opaque to translucent (tourmaline)

Fracture

Conchoidal (quartz), Uneven to conchoidal (tourmaline)

Cleavage

None (quartz), Poor/Indistinct (tourmaline)

Composition

SiO2 (quartz) with complex borosilicate (tourmaline)

Physical characteristics

• Crystal Habit: Quartz: Prismatic, often terminated. Tourmaline: Acicular, prismatic, columnar, often with striations parallel to the c-axis.
• Cleavage Type: Quartz: None. Tourmaline: Poor to indistinct on {1120} and {1011}.
• Fracture Type: Quartz: Conchoidal. Tourmaline: Uneven to conchoidal.
• Tenacity: Brittle for both minerals.
• Luster Type: Vitreous (glassy).

Explore Tourmalinated Quartz