How to identify Green Onyx

To correctly identify Green Onyx (Banded Calcite (often marketed as Onyx Marble or Green Onyx)), 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 mint green to deep forest green, often with white, yellow, or brown bands. The green is typically uniform within a band but varies between bands.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

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

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Fine-grained to medium-grained, often with a smooth, polished feel. The banding is a key textural feature.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Typically massive, microcrystalline to cryptocrystalline aggregates, forming stalactitic, stalagmitic, or layered structures. Individual calcite crystals are usually too small to be seen without magnification.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Perfect rhombohedral cleavage in three directions, though often not visible in massive, fine-grained specimens.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Forms in karst environments (caves) as speleothems (stalactites, stalagmites, flowstone) or in hot spring deposits (travertine). It is a secondary mineral formed by the precipitation of calcium carbonate from groundwater or hydrothermal fluids.

Key Facts

Hardness

3 (Mohs scale)

Specific Gravity

2.71 g/cm³

Crystal System

Trigonal

Color

Various shades of green, often banded with other colors.

Luster

Vitreous to waxy.

Transparency

Translucent to transparent.

Fracture

Conchoidal to uneven.

Cleavage

Perfect rhombohedral in three directions at 74°55'.

Composition

Calcium Carbonate (CaCO3).

Physical characteristics

• Crystal Habit: Massive, stalactitic, stalagmitic, columnar, granular, fibrous, lamellar, or rhombohedral crystals (rarely macroscopic).
• Cleavage Type: Perfect rhombohedral.
• Fracture Type: Conchoidal to uneven.
• Tenacity: Brittle.
• Luster Type: Vitreous (glassy) to waxy.

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