How to identify Carnelian Agate

To correctly identify Carnelian Agate (Chalcedony (SiO2) with iron oxide impurities), 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 or subtly mottled, unlike the distinct banding of typical agate.

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

   Microcrystalline, very fine-grained, smooth to slightly granular. Can feel cool and smooth to the touch.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Cryptocrystalline aggregates, typically massive, botryoidal, mammillary, or stalactitic. Individual crystals are microscopic and 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 and fissures of volcanic rocks (basalts, andesites, rhyolites), as well as 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

Crystal System

Trigonal (cryptocrystalline)

Color

Reddish-orange, orange-red, brownish-red

Luster

Waxy to vitreous

Transparency

Translucent to opaque

Fracture

Conchoidal

Cleavage

None

Composition

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

Physical characteristics

• Crystal Habit: Massive, botryoidal, mammillary, stalactitic, nodular, filling veins and cavities.
• Cleavage Type: None
• Fracture Type: Conchoidal to uneven
• Tenacity: Brittle
• Luster Type: Waxy to vitreous

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