How to identify Carnelian

To correctly identify Carnelian (Chalcedony (variety 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

   Ranges from pale orange to intense reddish-orange, brownish-red, and sometimes nearly blackish-red. 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) when polished; dull to waxy on rough surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Cryptocrystalline, meaning individual crystals are too small to be seen without high magnification. Feels smooth.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Typically occurs in botryoidal, mammillary, or stalactitic masses, or as nodular concretions filling cavities. Individual crystals are not visible to the naked eye.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None. Exhibits a conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in amygdaloidal cavities in volcanic rocks (e.g., basalt, andesite), in hydrothermal veins, and as pebbles in alluvial deposits derived from these primary sources. It can also occur in sedimentary formations.

Key Facts

Hardness

7 (Mohs scale)

Specific Gravity

2.58 - 2.64

Crystal System

Trigonal (cryptocrystalline aggregates)

Color

Reddish-orange, brownish-red, sometimes yellowish-orange

Luster

Waxy to vitreous

Transparency

Translucent to opaque

Fracture

Conchoidal

Cleavage

None

Composition

Silicon dioxide (SiO2) with iron oxide (hematite) inclusions

Physical characteristics

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

Explore Carnelian