How to identify Schorl Tourmaline in Quartz

To correctly identify Schorl Tourmaline in Quartz (SiO2 (Quartz) with NaFe3Al6(BO3)3Si6O18(OH)4 (Schorl 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 is typically colorless, white, or milky. Schorl tourmaline is opaque black.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Quartz has a vitreous (glassy) luster. Schorl tourmaline has a vitreous to resinous luster.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   The texture is typically crystalline, with the quartz forming a massive or crystalline matrix and the schorl appearing as distinct, often elongated, prismatic crystals embedded within.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz often forms hexagonal prisms with pyramidal terminations, or massive anhedral grains. Schorl forms characteristic trigonal or hexagonal prisms, often with striations parallel to the c-axis, and can be acicular (needle-like), columnar, or massive.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz has no true cleavage, exhibiting conchoidal fracture. Schorl tourmaline has very poor to indistinct cleavage parallel to the prism faces.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Pegmatites, hydrothermal veins, granitic intrusions, and regionally metamorphosed rocks.

Key Facts

Hardness

Quartz: 7 (Mohs); Schorl Tourmaline: 7-7.5 (Mohs)

Specific Gravity

Quartz: 2.65; Schorl Tourmaline: 3.0-3.2

Crystal System

Quartz: Trigonal; Schorl Tourmaline: Trigonal

Color

Quartz: Colorless, white, milky; Schorl Tourmaline: Opaque black

Luster

Vitreous

Transparency

Quartz: Transparent to translucent; Schorl Tourmaline: Opaque

Fracture

Quartz: Conchoidal; Schorl Tourmaline: Uneven to conchoidal

Cleavage

Quartz: None; Schorl Tourmaline: Very poor to indistinct

Composition

SiO2 (Quartz) and NaFe3Al6(BO3)3Si6O18(OH)4 (Schorl Tourmaline)

Physical characteristics

• Crystal Habit: Quartz: Prismatic, massive, granular; Schorl Tourmaline: Prismatic, acicular, columnar, massive, often with characteristic striations parallel to the c-axis.
• Cleavage Type: Quartz: None; Schorl Tourmaline: Very poor to indistinct on {1011} and {1120}.
• Fracture Type: Quartz: Conchoidal; Schorl Tourmaline: Uneven to conchoidal.
• Tenacity: Brittle for both minerals.
• Luster Type: Vitreous (glassy) for both.

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