How to identify Quartz in Matrix

To correctly identify Quartz in Matrix (SiO2 (Quartz) with host rock), 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 itself can be colorless (rock crystal), white (milky quartz), purple (amethyst), yellow (citrine), brown/black (smoky quartz), pink (rose quartz), or green (prasiolite). The matrix color will vary widely depending on its composition (e.g., grey granite, red sandstone, black basalt).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Quartz typically exhibits a vitreous (glassy) luster. The matrix luster can vary from dull/earthy to vitreous or metallic, depending on its constituent minerals.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Quartz crystals can be euhedral (well-formed), subhedral, or anhedral, often showing characteristic hexagonal prisms terminated by rhombohedra. The matrix texture will be characteristic of the host rock (e.g., granular in granite, clastic in sandstone, foliated in schist).

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz commonly forms hexagonal prisms with pyramidal terminations. It can also occur as massive, granular, or cryptocrystalline aggregates. The matrix will display the crystal forms of its constituent minerals or its overall rock fabric.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz lacks true cleavage, exhibiting conchoidal fracture. The matrix may or may not exhibit cleavage depending on its mineralogy (e.g., mica in schist will have perfect cleavage).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Quartz in matrix is found in a vast array of geological environments: hydrothermal veins and vugs in igneous, metamorphic, and sedimentary rocks; pegmatites; granitic intrusions; metamorphic schists and gneisses; and as a cementing agent or detrital component in sedimentary rocks. The specific environment dictates the nature of the matrix.

Key Facts

Hardness

7 on Mohs scale (for quartz); matrix hardness variable

Specific Gravity

2.65 g/cm³ (for quartz); matrix specific gravity variable

Crystal System

Trigonal (for quartz); matrix crystal systems variable

Color

Highly variable, depending on quartz variety and matrix composition

Luster

Vitreous (glassy) for quartz; matrix luster variable (e.g., dull, earthy, metallic)

Transparency

Transparent to translucent (for quartz); matrix transparency variable (e.g., opaque, translucent)

Fracture

Conchoidal (for quartz); matrix fracture variable

Cleavage

None (for quartz); matrix cleavage variable

Composition

SiO2 (Quartz) with various silicate, oxide, carbonate, or other mineral compositions in the host rock.

Physical characteristics

• Crystal Habit: Prismatic, often hexagonal, terminated by rhombohedra; massive, granular, cryptocrystalline. Matrix habit depends on its constituent minerals.
• Cleavage Type: None (quartz); matrix cleavage depends on its mineralogy.
• Fracture Type: Conchoidal (quartz); matrix fracture variable.
• Tenacity: Brittle (quartz); matrix tenacity variable.
• Luster Type: Vitreous (quartz); matrix luster variable (e.g., dull, earthy, sub-vitreous).

Explore Quartz in Matrix