How to identify Carnelian

To correctly identify Carnelian (Carnelian (a variety of Chalcedony)), 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

   Translucent to opaque, ranging from pale orange to reddish-orange, often with brownish undertones. The color is typically uniform but can show subtle banding.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Waxy to vitreous (glassy) on fractured surfaces, often duller on unpolished surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth to slightly granular, cryptocrystalline structure not visible to the naked eye.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Typically found as botryoidal, mammillary, or stalactitic masses, or as nodular concretions filling cavities. Individual crystals are microscopic.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None, due to its cryptocrystalline nature.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Occurs in volcanic rocks (e.g., basalts, andesites) filling amygdules and veins, in sedimentary rocks as nodules or concretions, and in hydrothermal veins. Often found in alluvial deposits as water-worn pebbles.

Key Facts

Hardness

6.5-7 on the Mohs scale

Specific Gravity

2.58-2.64

Crystal System

Trigonal (cryptocrystalline aggregates)

Color

Pale orange to reddish-orange, brownish-red

Luster

Waxy to vitreous

Transparency

Translucent to opaque

Fracture

Conchoidal to uneven

Cleavage

None

Composition

Silicon dioxide (SiO2) with iron oxide impurities

Physical characteristics

• Crystal Habit: Cryptocrystalline aggregates, typically massive, botryoidal, mammillary, or stalactitic. Individual crystals are microscopic and fibrous.
• Cleavage Type: None
• Fracture Type: Conchoidal to uneven, splintery in some varieties.
• Tenacity: Brittle
• Luster Type: Waxy to vitreous

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