How to identify Carnelian

To correctly identify Carnelian (Chalcedony (SiO2) 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, deep red, and brownish-red. The color is generally uniform but can show subtle banding or cloudiness.

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

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

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Typically massive, botryoidal, or stalactitic; individual crystals are microscopic and not discernible.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None. Carnelian, like all chalcedony, lacks cleavage due to its cryptocrystalline nature.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in amygdaloidal cavities and veins within volcanic rocks (e.g., basalt, andesite), and in sedimentary deposits (e.g., gravels, conglomerates) where it has been eroded from its primary source.

Key Facts

Hardness

6.5-7 on the Mohs scale

Specific Gravity

2.58-2.64 g/cm³

Crystal System

Trigonal (cryptocrystalline aggregate)

Color

Reddish-orange, deep red, brownish-red

Luster

Waxy to vitreous

Transparency

Translucent to opaque

Fracture

Conchoidal to uneven

Cleavage

None

Composition

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

Physical characteristics

• Crystal Habit: Massive, botryoidal, stalactitic, nodular; cryptocrystalline aggregates.
• Cleavage Type: Absent
• Fracture Type: Conchoidal to uneven
• Tenacity: Brittle
• Luster Type: Waxy to vitreous

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