How to identify Quartz with Epidote

To correctly identify Quartz with Epidote (SiO2 (Quartz) with 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 is typically colorless, white, or milky. Epidote ranges from pistachio-green to yellowish-green, brownish-green, or blackish-green. The combination will show clear to milky quartz with green inclusions or intergrowths.

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 vary from massive to crystalline. Epidote often forms prismatic crystals, acicular (needle-like) crystals, 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 prismatic crystals, often striated parallel to the length. When intergrown, epidote crystals may be embedded randomly or aligned within the quartz.

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), hydrothermal veins, contact metamorphic zones, 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

Colorless, white, or milky (quartz) with pistachio-green to dark-green (epidote).

Luster

Vitreous.

Transparency

Quartz: Transparent to translucent. Epidote: Translucent to opaque.

Fracture

Quartz: Conchoidal. Epidote: Uneven to subconchoidal.

Cleavage

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

Composition

Quartz: Silicon dioxide (SiO2). Epidote: Calcium aluminum iron sorosilicate hydroxide (Ca2(Al,Fe)3(SiO4)3(OH)).

Physical characteristics

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

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