sedimentary

Limestone with Quartz Vugs

CaCO3 with SiO2 inclusions

Mohs hardness 3 for host rock and 7 for quartz; color varies from tan, brown to white; vitreous to earthy luster; trigonal crystal system for quartz.

Identified November 2, 2026More sedimentary →

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Physical properties

Mohs hardness 3 for host rock and 7 for quartz; color varies from tan, brown to white; vitreous to earthy luster; trigonal crystal system for quartz.

Formed through the accumulation of marine organism shells and subsequent hydrothermal mineral precipitation filling cavities over millions of years.

Used primarily in aggregate, construction, and educational specimen collection.

Cavities lined with crystals are known as vugs or geodes, often forming when mineral-rich water percolates through porous sedimentary layers.

Identify by testing for effervescence with dilute hydrochloric acid on the matrix while noting the harder quartz crystals lining the cavities.

Fossil-bearing concretion, possibly containing a fossil shell or other organic inclusion

Calcareous concretion; exact fossil and host-rock composition are not identifiable from the image

Fossiliferous Sedimentary Rock

Sedimentary limestone with invertebrate fossil imprint

Sandstone or Siltstone

Arenite (if sandstone)

Sandstone

Arenite

Shale

Shale (clastic sedimentary rock)

Shale (or Mudstone/Siltstone)

Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)