Where is Calcite-cemented Sandstone found?
Calcite (CaCO3) in Sandstone
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Open the appCalcite-cemented Sandstone occurs in specific geological environments. Knowing where to look, and in what kind of rock, is the difference between going home empty-handed and finding a great specimen.
Where to find Calcite-cemented Sandstone
Colorado Plateau, USA
Many Mesozoic sandstones (e.g., Navajo Sandstone, Entrada Sandstone) exhibit calcite cementation, contributing to their distinctive weathering patterns and cliff-forming characteristics.
North Sea Basin, Europe
Important reservoir rocks for oil and gas, where calcite cementation can significantly impact porosity and permeability.
Appalachian Basin, USA
Various Paleozoic sandstones, such as those in the Oriskany Formation, can be calcite-cemented.
Australia (e.g., Perth Basin)
Sedimentary basins often contain calcite-cemented sandstones, particularly in coastal and shallow marine sequences.
Collecting tips
- Acid Test. A definitive test for calcite is its reaction with dilute hydrochloric acid (HCl). Calcite will effervesce vigorously, producing CO2 gas. Apply a small drop of 10% HCl to a fresh surface; observe for bubbles. This distinguishes it from quartz or other silicate cements.
- Hardness Test. Calcite has a Mohs hardness of 3. While the overall sandstone hardness will be influenced by the detrital grains (e.g., quartz at 7), the calcite cement itself can be scratched by a copper coin (hardness 3.5).
- Cleavage Observation. Look for the characteristic rhombohedral cleavage of calcite in any visible crystalline areas of the cement, especially under magnification.
- Field Context. Consider the geological setting. If nearby limestones or shell beds are present, it increases the likelihood of calcite cementation in associated sandstones.
Quick Check
- Color:
- Variable (light grey, tan, buff, reddish-brown), often with white or colorless cement.
- Luster:
- Dull to earthy for the rock, vitreous to pearly for visible calcite.
- Streak:
- White (for calcite component).
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