sedimentary

Geodal Limestone / Calcite Druze

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Tan, beige, to off-white; Luster: Vitreous to pearly crystals on a dull earthy matrix; Crystal Structure: Trigonal/Rhombohedral; Cleavage: Perfect rhombohedral in crystal areas; Specific Gravity: 2.71

Hardness: 3 on Mohs scale
Color: Tan, beige, to off-white
Luster: Vitreous to pearly crystals on a dull earthy matrix

Identified March 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the chemical precipitation of calcium carbonate from groundwater within cavities (vugs) of limestone or dolostone bedrock. These often date from the Paleozoic to Mesozoic eras and form in marine environments or karst landscapes.

Uses & applications

Primarily used as decorative garden stones, aquarium rocks, or entry-level mineral specimens for collectors. Industrial grade limestone is used in cement production and as a soil conditioner.

Geological facts

Vuggy limestone like this specimen often contains 'druze'—tiny sparkling crystal coatings. If a drop of vinegar or weak acid is applied, the specimen will fizz (effervesce) due to the release of carbon dioxide gas.

Field identification & locations

Identify in the field by its relatively soft surface (rank with a copper penny) and the presence of small botryoidal or crystalline clusters in hollows. Commonly found in road cuts or quarries in the Midwest USA and other limestone-rich regions.

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