How to identify Red Coral

To correctly identify Red Coral (Corallium rubrum), 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 pink (angel skin coral) to deep ox-blood red. Can also be orange-red.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to waxy when unpolished; vitreous (glassy) when polished.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth when polished; naturally exhibits a fine granular or fibrous texture. May show growth rings or a porous surface in unpolished specimens.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Amorphous to cryptocrystalline (calcite microcrystals). Forms branching, tree-like structures.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None (amorphous/cryptocrystalline structure).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Deep-water marine environments, typically on rocky seabeds or submerged caves, at depths ranging from 10 to 300 meters (33 to 984 feet). Requires stable temperatures, moderate currents, and low light conditions.

Key Facts

Hardness

3 to 4 on the Mohs scale (relatively soft)

Specific Gravity

2.6 to 2.7

Crystal System

Amorphous to cryptocrystalline (composed of microcrystalline calcite)

Color

Various shades of red, pink, and orange-red

Luster

Waxy to vitreous

Transparency

Opaque

Fracture

Splintery to conchoidal

Cleavage

None

Composition

Primarily calcium carbonate (CaCO3) in the form of calcite, with organic binders.

Physical characteristics

• Crystal Habit: Branching, arborescent (tree-like) structures, often massive or columnar.
• Cleavage Type: Absent
• Fracture Type: Splintery to conchoidal, uneven.
• Tenacity: Brittle
• Luster Type: Waxy to vitreous (when polished)

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