How to identify Quartz with Epidote

To correctly identify Quartz with Epidote (SiO2 (Quartz) and Ca2(Al,Fe)3(SiO4)3(OH) (Epidote)), 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 can be colorless, white, gray, or smoky. Epidote typically presents as pistachio-green, yellowish-green, or dark green. The combination will show these colors.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Quartz: Vitreous. Epidote: Vitreous to resinous.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Can range from massive to crystalline. Epidote often forms prismatic crystals, acicular (needle-like) inclusions, or granular aggregates within the quartz matrix.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz: Hexagonal prisms with pyramidal terminations. Epidote: Monoclinic, typically forming elongated, prismatic crystals, often striated parallel to the length. Can also be granular or massive.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz: None (conchoidal fracture). Epidote: Perfect on {001}, good on {100}.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Metamorphic rocks (schists, gneisses, amphibolites), contact metamorphic zones, hydrothermal veins, and altered igneous rocks.

Key Facts

Hardness

Quartz: 7 (Mohs). Epidote: 6-7 (Mohs).

Specific Gravity

Quartz: 2.65. Epidote: 3.35-3.47.

Crystal System

Quartz: Trigonal. Epidote: Monoclinic.

Color

Quartz: Colorless, white, gray, smoky. Epidote: Pistachio-green, yellowish-green, dark green.

Luster

Vitreous to resinous.

Transparency

Quartz: Transparent to translucent. Epidote: Transparent to translucent.

Fracture

Quartz: Conchoidal. Epidote: Uneven to subconchoidal.

Cleavage

Quartz: None. Epidote: Perfect on {001}, good on {100}.

Composition

SiO2 (Quartz) and Ca2(Al,Fe)3(SiO4)3(OH) (Epidote).

Physical characteristics

• Crystal Habit: Quartz: Prismatic, massive, granular. Epidote: Prismatic, acicular, granular, massive.
• Cleavage Type: Quartz: Absent. Epidote: Perfect basal cleavage {001}, good {100}.
• Fracture Type: Quartz: Conchoidal. Epidote: Uneven to subconchoidal.
• Tenacity: Brittle.
• Luster Type: Vitreous to resinous.

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