How to identify Banded Onyx Marble

To correctly identify Banded Onyx Marble (Calcite (a variety of 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

   Highly variable, often white, cream, yellow, green, brown, red, or a combination of these colors in distinct bands. Impurities dictate the color variations.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to waxy, sometimes dull on unpolished surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Fine-grained to microcrystalline, often compact. Can exhibit a sugary texture on fractured surfaces.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Typically massive, banded, stalactitic, or botryoidal aggregates of microcrystalline 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 not at 90 degrees), though often not apparent in massive, fine-grained material.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Forms in karstic environments (caves, sinkholes) as speleothems (stalactites, stalagmites, flowstone) or near hot/cold springs where calcium-rich waters precipitate calcite. It is a chemical sedimentary deposit.

Key Facts

Hardness

3 (Mohs scale)

Specific Gravity

2.71 g/cm³

Crystal System

Trigonal

Color

Highly variable, often banded in white, cream, yellow, green, brown, red

Luster

Vitreous to waxy

Transparency

Translucent to opaque

Fracture

Conchoidal to uneven

Cleavage

Perfect rhombohedral (3 directions at 74°55')

Composition

Calcium Carbonate (CaCO3)

Physical characteristics

• Crystal Habit: Massive, banded, stalactitic, botryoidal, granular aggregates
• Cleavage Type: Rhombohedral
• Fracture Type: Conchoidal to uneven
• Tenacity: Brittle
• Luster Type: Vitreous to waxy

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