How to identify Chlorite-Epidote Quartz

To correctly identify Chlorite-Epidote Quartz (SiO2 (Quartz) with associated silicates), 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 smoky. Chlorite inclusions impart shades of green (pale to dark, sometimes brownish-green). Epidote inclusions impart pistachio-green, yellowish-green, or olive-green. The color can be uniform or patchy depending on the distribution of the inclusions.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) for quartz; chlorite can be dull to pearly; epidote is typically vitreous to resinous.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Crystalline, often with visible inclusions. Quartz can be massive or euhedral. Chlorite can be fine-grained, flaky, or form distinct crystals. Epidote can be acicular, granular, or prismatic.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz typically forms hexagonal prisms terminating in rhombohedra. Chlorite forms platy or micaceous crystals, often in aggregates. Epidote forms prismatic crystals, often striated, or granular masses.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz has no true cleavage, exhibiting conchoidal fracture. Chlorite has perfect basal cleavage (one direction). Epidote has perfect cleavage in one direction ({001}) and good in another ({100}).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, metamorphic rocks (greenschist to amphibolite facies), contact metamorphic zones, and sometimes in altered igneous rocks. Often found in areas with significant tectonic activity and fluid flow.

Key Facts

Hardness

Quartz: 7 on Mohs scale. Chlorite: 2-2.5. Epidote: 6-7. The overall hardness will be dominated by quartz.

Specific Gravity

Quartz: 2.65 g/cm³. Chlorite: 2.6-3.3 g/cm³. Epidote: 3.3-3.5 g/cm³. The aggregate specific gravity will be slightly higher than pure quartz depending on inclusion density.

Crystal System

Quartz: Trigonal. Chlorite: Monoclinic. Epidote: Monoclinic.

Color

Colorless, white, or smoky quartz with green (chlorite) or pistachio-green (epidote) inclusions.

Luster

Vitreous (glassy) for quartz and epidote; dull to pearly for chlorite.

Transparency

Transparent to translucent for quartz; inclusions can be opaque to translucent.

Fracture

Conchoidal for quartz. Chlorite is splintery/uneven. Epidote is uneven.

Cleavage

Quartz: None. Chlorite: Perfect basal cleavage. Epidote: Perfect in one direction, good in another.

Composition

SiO2 (Quartz) with hydrous magnesium-iron-aluminum silicates (Chlorite) or calcium-aluminum-iron silicates (Epidote).

Physical characteristics

• Crystal Habit: Quartz: Prismatic, massive, granular. Chlorite: Micaceous, platy, massive, fibrous. Epidote: Prismatic, acicular, granular, massive.
• Cleavage Type: Quartz: None. Chlorite: Perfect basal. Epidote: Perfect {001}, good {100}.
• Fracture Type: Quartz: Conchoidal. Chlorite: Uneven, splintery. Epidote: Uneven.
• Tenacity: Quartz: Brittle. Chlorite: Flexible, inelastic. Epidote: Brittle.
• Luster Type: Quartz: Vitreous. Chlorite: Dull to pearly. Epidote: Vitreous to resinous.

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