How to identify Tourmalinated Quartz

To correctly identify Tourmalinated Quartz (SiO2 with (Na,Ca)(Mg,Fe,Li,Al)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 can be colorless, white, gray, or smoky. Tourmaline inclusions are typically black (schorl), but can rarely be green, pink, or other colors 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

   Crystalline, with distinct tourmaline needles or prisms embedded within a quartz matrix. The quartz itself can be massive or euhedral.

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 characteristic striations parallel to the c-axis, and often appears as acicular (needle-like) inclusions within the quartz.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz: None (conchoidal fracture). Tourmaline: Poor basal cleavage, often not observed in inclusions.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Pegmatites, hydrothermal veins, and regionally metamorphosed rocks. It is often found in granitic intrusions and associated dikes.

Key Facts

Hardness

Quartz: 7 (Mohs). Tourmaline: 7-7.5 (Mohs).

Specific Gravity

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

Crystal System

Quartz: Trigonal. Tourmaline: Trigonal.

Color

Quartz: colorless, white, gray, smoky. Tourmaline: black (most common), green, pink, blue, etc.

Luster

Vitreous.

Transparency

Quartz: Transparent to translucent. Tourmaline: Opaque to transparent.

Fracture

Quartz: Conchoidal. Tourmaline: Uneven to conchoidal.

Cleavage

Quartz: None. Tourmaline: Poor basal cleavage.

Composition

Quartz: Silicon dioxide (SiO2). Tourmaline: Complex borosilicate with variable composition (Na,Ca)(Mg,Fe,Li,Al)3Al6(BO3)3Si6O18(OH)4.

Physical characteristics

• Crystal Habit: Quartz: Prismatic, massive, granular. Tourmaline: Prismatic, acicular, columnar, massive. Inclusions are typically acicular or slender prismatic.
• Cleavage Type: Quartz: Absent. Tourmaline: Poor, indistinct.
• Fracture Type: Conchoidal (quartz), uneven to conchoidal (tourmaline).
• Tenacity: Brittle.
• Luster Type: Vitreous.

Explore Tourmalinated Quartz