sedimentary
Caliche (with Lichen Cover)
Calcium carbonate-cemented soil layer (CaCO3)
Hardness: 2-3 (Mohs scale), Color: White to pinkish-gray (covered in white/orange crustose lichen), Luster: Dull/Earthy, Structure: Amorphous or microcrystalline crusts, Specific Gravity: 2.1-2.6
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Physical properties
Hardness: 2-3 (Mohs scale), Color: White to pinkish-gray (covered in white/orange crustose lichen), Luster: Dull/Earthy, Structure: Amorphous or microcrystalline crusts, Specific Gravity: 2.1-2.6
Formation & geological history
Formed by the accumulation of calcium carbonate in arid or semi-arid soils. Over thousands of years, rainwater leaches minerals downward where they precipitate as a hard cement layer. Most common in Quaternary deposits.
Uses & applications
Used in road construction as base material, as an agricultural soil amendment to adjust pH, and sometimes in low-grade building materials. Not typically used in jewelry.
Geological facts
Caliche are often called 'hardpan.' In the Mojave Desert and Southwestern US, these layers can be so hard they require jackhammers to penetrate for plumbing or foundation work. The white and orange patterns on this specimen are actually crustose lichens living on the rock surface.
Field identification & locations
Identified by its white, chalky appearance and strong effervescence when exposed to a weak acid like vinegar. Found throughout the Southwestern US, Mexico, and Australia. Collectors should look for unique botryoidal or layered structures within the crust.
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