How to identify Smoky Quartz and Carnelian

To correctly identify Smoky Quartz and Carnelian (SiO2 (Smoky Quartz), SiO2 (Carnelian)), 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

   Smoky Quartz: Ranges from light gray-brown to dark brown, often translucent, sometimes nearly opaque black (Morion). Carnelian: Translucent to opaque, reddish-orange to brownish-red, sometimes with a slightly waxy appearance.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Smoky Quartz: Vitreous (glassy). Carnelian: Waxy to dull, sometimes vitreous when polished.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smoky Quartz: Smooth, conchoidal fracture surfaces. Carnelian: Smooth, often microcrystalline, conchoidal to splintery fracture.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Smoky Quartz: Typically forms hexagonal prisms with pyramidal terminations, or massive. Carnelian: Cryptocrystalline, forming botryoidal, mammillary, or nodular masses; rarely forms macroscopic crystals.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Both Smoky Quartz and Carnelian lack true cleavage. They exhibit conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Smoky Quartz: Granitic pegmatites, hydrothermal veins, metamorphic rocks. Carnelian: Volcanic rocks (e.g., basalt, andesite) filling amygdules or veins, sedimentary deposits (alluvial gravels).

Key Facts

Hardness

7 on the Mohs scale (for both)

Specific Gravity

2.65 (for both)

Crystal System

Trigonal (for both)

Color

Smoky Quartz: Gray-brown to black; Carnelian: Reddish-orange to brownish-red

Luster

Smoky Quartz: Vitreous; Carnelian: Waxy to dull

Transparency

Smoky Quartz: Translucent to opaque; Carnelian: Translucent to opaque

Fracture

Conchoidal (for both)

Cleavage

None (for both)

Composition

Silicon dioxide (SiO2) with trace impurities

Physical characteristics

• Crystal Habit: Smoky Quartz: Prismatic, often with hexagonal cross-section and pyramidal terminations, also massive. Carnelian: Cryptocrystalline, massive, botryoidal, nodular.
• Cleavage Type: None
• Fracture Type: Conchoidal
• Tenacity: Brittle
• Luster Type: Smoky Quartz: Vitreous; Carnelian: Waxy to dull

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