sedimentary

Quartz Calcite Vug in Limestone

Calcium Carbonate (CaCO3) with Silicon Dioxide (SiO2) inclusions

AI-generated identification · may be incorrect

Hardness: 3 (limestone/calcite) to 7 (quartz); Color: Grey matrix with clear to white crystals; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: Perfect rhombohedral in calcite portions.

Hardness: 3 (limestone/calcite) to 7 (quartz)
Color: Grey matrix with clear to white crystals
Luster: Vitreous to dull

Identified June 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine environments through the accumulation of calcium carbonate shells and skeletons. The crystal vug (cavity) formed later via hydrothermal fluids or groundwater precipitation filling voids within the sedimentary rock, typically during the Paleozoic era.

Uses & applications

Limestone is used extensively in construction, cement production, and as an industrial flux. The crystal specimen itself is primarily for educational or amateur collecting.

Geological facts

Vugs like these are essentially 'mini-geodes' that form when acidic water dissolves a hole in the limestone and mineral-rich water later precipitates crystals into the space. Herkimer diamonds are a famous specialized version of this phenomenon.

Field identification & locations

Identify in the field by checking for the fizz reaction to hydrochloric acid on the grey matrix (calcite) and the inability of a steel knife to scratch the clear crystals (if they are quartz). Commonly found in quarry outcrops and road cuts in karst topographies.