How to identify Caliche

To correctly identify Caliche (Pedogenic Calcrete), 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, off-white, cream, light gray, or pale brown, depending on impurities.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to earthy, sometimes chalky.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Highly variable; can be powdery, nodular, platy, laminar, or massive and hard. Often contains embedded clasts of other rocks or soil particles.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Microcrystalline to cryptocrystalline calcite, often forming coatings, cements, or nodules. Individual crystals are rarely visible to the naked eye.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Not applicable as a rock; individual calcite grains within caliche exhibit rhombohedral cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Forms in the vadose zone of soils in arid to semi-arid regions, often associated with grasslands, deserts, and Mediterranean climates. Found in ancient soil profiles (paleosols).

Key Facts

Hardness

Variable, from 1 (powdery) to 3-4 (hard, cemented) on the Mohs scale, depending on the degree of cementation.

Specific Gravity

2.0 - 2.7, depending on porosity and impurities.

Crystal System

Not applicable as a rock; constituent calcite is trigonal.

Color

White, cream, light gray, pale brown.

Luster

Dull, earthy, chalky.

Transparency

Opaque.

Fracture

Conchoidal to irregular in hard varieties; crumbly in soft varieties.

Cleavage

Not applicable as a rock; constituent calcite has perfect rhombohedral cleavage.

Composition

Primarily calcium carbonate (CaCO3) in the form of calcite, with varying amounts of quartz, feldspar, clay minerals, and other detrital components.

Physical characteristics

• Crystal Habit: Microcrystalline to cryptocrystalline aggregates, coatings, nodules, or massive layers.
• Cleavage Type: Not applicable for the rock; calcite exhibits perfect rhombohedral cleavage.
• Fracture Type: Irregular to conchoidal (for hard varieties), earthy (for soft varieties).
• Tenacity: Brittle when hard; friable when soft.
• Luster Type: Dull to earthy.

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