How to identify Included Quartz

To correctly identify Included Quartz (SiO2 with unknown dark mineral), 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 is typically colorless, white, or smoky. Inclusions are dark (black, dark brown, dark green, dark red).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) for the quartz matrix.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth to conchoidal fracture for quartz. Inclusions may have their own characteristic textures.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Hexagonal prisms terminated by rhombohedra for quartz. Inclusions may show their own crystal habits if well-formed (e.g., acicular tourmaline).

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None for quartz. Inclusions may exhibit cleavage if they are well-formed crystals.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, pegmatites, metamorphic rocks, and sometimes sedimentary environments where quartz recrystallizes.

Key Facts

Hardness

7 on the Mohs scale (for quartz). The hardness of inclusions may vary but is generally less than quartz.

Specific Gravity

2.65 g/cm³ (for pure quartz). May vary slightly depending on the density and proportion of inclusions.

Crystal System

Trigonal (for quartz).

Color

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

Luster

Vitreous.

Transparency

Transparent to translucent (for quartz matrix). Inclusions are typically opaque.

Fracture

Conchoidal (for quartz).

Cleavage

None (for quartz).

Composition

SiO2 (quartz) with various dark mineral inclusions (e.g., iron oxides, tourmaline, chlorite, amphiboles, carbonaceous material).

Physical characteristics

• Crystal Habit: Prismatic, often terminated by rhombohedra. Inclusions can be acicular, tabular, granular, or amorphous within the quartz.
• Cleavage Type: Absent (for quartz).
• Fracture Type: Conchoidal (for quartz).
• Tenacity: Brittle (for quartz).
• Luster Type: Vitreous.

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