How to identify Quartz and Granite

To correctly identify Quartz and Granite (SiO2 (Quartz), Igneous rock (Granite)), 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

   Granite: Typically light-colored (white, gray, pink, red). Quartz: Colorless, white, purple (amethyst), yellow (citrine), brown (smoky quartz), pink (rose quartz), green (prasiolite), black (morion).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Granite: Overall dull to vitreous due to constituent minerals. Quartz: Vitreous (glassy) to greasy.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Granite: Phaneritic (coarse-grained), interlocking crystalline texture. Quartz: Crystalline, often anhedral in granite, but can form euhedral hexagonal prisms with pyramidal terminations in vugs or veins.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Granite: Granular, interlocking crystals of quartz, feldspar, and mica. Quartz: Hexagonal prisms with pyramidal terminations (when euhedral), massive, granular.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Granite: No overall cleavage, but constituent minerals like feldspar and mica exhibit cleavage. Quartz: None (conchoidal fracture).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Granite: Intrusive igneous bodies (batholiths, stocks, dikes, sills) in continental crust, often associated with orogenic belts. Quartz: Ubiquitous in igneous, metamorphic, and sedimentary rocks; hydrothermal veins, pegmatites, sandstones, quartzites.

Key Facts

Hardness

Granite: 6-7 (overall, due to constituent minerals). Quartz: 7 (Mohs scale).

Specific Gravity

Granite: 2.65-2.75 g/cm³. Quartz: 2.65 g/cm³.

Crystal System

Granite: Not applicable (rock). Quartz: Trigonal.

Color

Granite: White, gray, pink, red. Quartz: Colorless, white, purple, yellow, brown, pink, green, black.

Luster

Granite: Vitreous to dull. Quartz: Vitreous to greasy.

Transparency

Granite: Opaque. Quartz: Transparent to translucent.

Fracture

Granite: Irregular to conchoidal (within quartz grains). Quartz: Conchoidal.

Cleavage

Granite: None (as a rock), but constituent feldspar has good cleavage. Quartz: None.

Composition

Granite: Primarily quartz, feldspar (orthoclase, plagioclase), mica (biotite, muscovite). Quartz: Silicon dioxide (SiO2).

Physical characteristics

• Crystal Habit: Granite: Granular, massive. Quartz: Prismatic, massive, granular, cryptocrystalline (e.g., chalcedony).
• Cleavage Type: Granite: Not applicable (rock). Quartz: Absent.
• Fracture Type: Granite: Irregular to subconchoidal. Quartz: Conchoidal.
• Tenacity: Granite: Brittle. Quartz: Brittle.
• Luster Type: Granite: Vitreous to dull. Quartz: Vitreous to greasy.

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