How to identify Travertine

To correctly identify Travertine (Calcium Carbonate (CaCO3)), 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

   Typically white, cream, tan, beige, brown, or reddish-brown. Colors are often banded or mottled.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to earthy, sometimes waxy on polished surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Porous, often with visible voids and cavities. Can be fibrous, concentric, or massive. Unpolished surfaces are typically rough.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Microcrystalline to cryptocrystalline aggregates of calcite. Individual crystals are rarely macroscopic.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Not typically observed in hand samples due to its microcrystalline nature and porous texture. Calcite, the primary mineral, has perfect rhombohedral cleavage (three directions at 74° and 106°).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Forms in terrestrial environments, specifically around hot springs, cold springs, and in caves (as speleothems like stalactites and stalagmites, though these are often denser and less porous than surface travertine). It is a product of chemical precipitation from calcium-rich waters.

Key Facts

Hardness

3 on the Mohs scale (due to its calcite composition)

Specific Gravity

2.71 (for pure calcite, but can be lower for porous travertine, ranging from 2.3 to 2.7)

Crystal System

Trigonal (for calcite, the primary mineral)

Color

White, cream, tan, beige, brown, reddish-brown

Luster

Dull, earthy, sometimes waxy

Transparency

Opaque to translucent

Fracture

Uneven to conchoidal (for individual calcite crystals, but often irregular due to porosity)

Cleavage

Perfect rhombohedral (for calcite, but not typically visible in the rock)

Composition

Primarily Calcium Carbonate (CaCO3), with minor impurities like iron oxides, clay minerals, and organic matter.

Physical characteristics

• Crystal Habit: Microcrystalline to cryptocrystalline aggregates, often forming fibrous, concentric, or massive structures. Can be botryoidal or stalactitic.
• Cleavage Type: Perfect rhombohedral (of constituent calcite crystals)
• Fracture Type: Uneven to irregular, sometimes conchoidal in denser varieties
• Tenacity: Brittle
• Luster Type: Dull to earthy, sometimes waxy on polished surfaces

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