How to identify Green Onyx

To correctly identify Green Onyx (Banded Calcite (variety of Onyx Marble)), 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 green to dark green, often with white, cream, or brown bands. The green color is due to impurities.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to waxy on fresh surfaces, can be dull if unpolished or weathered.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Fine-grained to medium-grained, often with a smooth, polished feel. Exhibits distinct banding or swirling patterns.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Typically massive, microcrystalline to cryptocrystalline aggregates of calcite. Individual crystals are usually not visible to the naked eye.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Perfect rhombohedral cleavage (three directions at 74° and 106°), though often not apparent in massive forms unless fractured or stressed.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Forms in karstic cave systems as speleothems (stalactites, stalagmites, flowstone) or as precipitates from mineral-rich hot springs and geysers (travertine deposits). Requires a source of calcium carbonate-saturated water and conditions for precipitation.

Key Facts

Hardness

3 (Mohs scale)

Specific Gravity

2.71 g/cm³

Crystal System

Trigonal

Color

Green (various shades), often banded

Luster

Vitreous to waxy

Transparency

Translucent to opaque

Fracture

Conchoidal to uneven

Cleavage

Perfect rhombohedral (3 directions at 74° and 106°)

Composition

Calcium Carbonate (CaCO₃) with impurities causing green coloration

Physical characteristics

• Crystal Habit: Massive, stalactitic, stalagmitic, columnar, granular, fibrous, lamellar
• Cleavage Type: Perfect rhombohedral
• Fracture Type: Conchoidal to uneven
• Tenacity: Brittle
• Luster Type: Vitreous to waxy

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