Limestone (specifically Dolomitic Limestone)

Physical Properties

Hardness: 3.5 to 4 on Mohs scale. Color: Gray, tan, or yellowish-brown. Luster: Dull to earthy. Crystal Structure: Trigonal (often microcrystalline). Cleavage: Rhombohedral (though usually not visible in massive specimens). Specific Gravity: 2.8 to 2.9.

Formation & Geological History

Formed through the chemical replacement of calcium in limestone by magnesium-rich groundwater (dolomitization), or through direct precipitation in hypersaline marine environments. Most common in ancient Paleozoic sequences.

Uses & Applications

Used heavily in construction as aggregate for concrete and asphalt, as a soil conditioner (agricultural lime), in the production of glass and bricks, and as a source of magnesium oxide.

Geological Facts

Unlike calcite-based limestone, dolomite typically does not bubble immediately when cold dilute hydrochloric acid is applied; it usually requires the rock to be powdered first to react.

Field Identification & Locations

Identify in the field by its blocky fracturing and a weak reaction to acid compared to pure limestone. Often found in massive outcrops and stream beds in regions with carbonate bedrock.

Identified on: 4/27/2026

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