How to identify Green Onyx

To correctly identify Green Onyx (Calcite (variety of banded calcite or travertine)), 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, cream, or brown banding. The green color is typically uniform within bands but can vary between bands.

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. Banding is a key textural feature.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Typically massive, microcrystalline to cryptocrystalline aggregates, forming banded layers. Individual calcite 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, not at 90 degrees), though often not apparent in massive, fine-grained material unless broken or observed under magnification.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Forms in karstic environments (caves, as speleothems like stalactites and stalagmites), around hot springs and geysers (as travertine), or in other settings where calcium-rich waters precipitate calcite. The green coloration indicates the presence of specific impurities during formation.

Key Facts

Hardness

3 (Mohs scale)

Specific Gravity

2.71 g/cm³

Crystal System

Trigonal

Color

Various shades of green, often banded

Luster

Vitreous to waxy

Transparency

Translucent to semi-translucent

Fracture

Conchoidal to uneven

Cleavage

Perfect rhombohedral (3 directions at 74°55')

Composition

Calcium Carbonate (CaCO3)

Physical characteristics

• Crystal Habit: Massive, microcrystalline to cryptocrystalline aggregates, often forming banded layers (speleothems, travertine).
• Cleavage Type: Perfect rhombohedral, typically not observed in massive material unless fractured.
• Fracture Type: Conchoidal to uneven, splintery.
• Tenacity: Brittle.
• Luster Type: Vitreous (glassy) to waxy, sometimes dull.

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