How to identify Schorl in Quartz

To correctly identify Schorl in Quartz (Schorl (Black Tourmaline) with Quartz), 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

   The schorl inclusions are opaque black, while the quartz matrix is typically colorless, white, or milky white, sometimes smoky or slightly yellowish.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Schorl exhibits a vitreous to resinous luster, while quartz has a vitreous luster.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   The texture is characterized by the sharp, often elongated, black crystals of schorl embedded within the glassy, often massive, quartz matrix.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Schorl crystals are typically prismatic, often with characteristic striations parallel to the c-axis, and a pseudo-hexagonal cross-section. Quartz crystals are typically hexagonal prisms terminating in hexagonal pyramids, or massive anhedral forms.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Schorl has poor to indistinct cleavage, often appearing as conchoidal to uneven fracture. Quartz has no cleavage, exhibiting conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in granitic pegmatites, hydrothermal veins, and some metamorphic rocks. It is indicative of boron-rich, silica-saturated environments.

Key Facts

Hardness

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

Specific Gravity

Schorl: 3.03-3.25; Quartz: 2.65

Crystal System

Schorl: Trigonal; Quartz: Trigonal

Color

Opaque black (schorl); Colorless, white, milky white, sometimes smoky (quartz)

Luster

Vitreous to resinous (schorl); Vitreous (quartz)

Transparency

Opaque (schorl); Transparent to translucent (quartz)

Fracture

Conchoidal to uneven (schorl); Conchoidal (quartz)

Cleavage

Poor to indistinct (schorl); None (quartz)

Composition

Schorl: NaFe3Al6(BO3)3Si6O18(OH)4; Quartz: SiO2

Physical characteristics

• Crystal Habit: Schorl: Prismatic, acicular, columnar, often striated parallel to c-axis. Quartz: Prismatic, massive, granular.
• Cleavage Type: Schorl: Poor to indistinct on {1011} and {1120}. Quartz: None.
• Fracture Type: Schorl: Conchoidal to uneven. Quartz: Conchoidal.
• Tenacity: Brittle (both schorl and quartz)
• Luster Type: Vitreous to resinous (schorl); Vitreous (quartz)

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