Where is Calcite on Sandstone found?
Calcite (CaCO3) on Sandstone
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Open the appCalcite on 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 on Sandstone
Colorado Plateau, USA
Known for extensive sandstone formations (e.g., Navajo Sandstone, Entrada Sandstone) where calcite cementation is common, often forming concretions or localized hardened zones.
Midwestern United States
Many Paleozoic sandstone units (e.g., St. Peter Sandstone) exhibit varying degrees of calcite cementation due to diagenetic processes related to overlying carbonate sequences.
North Africa and Middle East
Desert environments with extensive sandstone deposits often show calcite cementation, sometimes forming 'desert roses' or other concretions where calcite precipitates from evaporating groundwater.
European Sedimentary Basins
Various Mesozoic and Cenozoic sandstone formations across Europe (e.g., Paris Basin, North Sea Basin) contain calcite-cemented intervals, important for hydrocarbon exploration.
Collecting tips
- Look for Hardened Zones. Calcite cementation often makes sandstone more resistant to weathering. Look for areas within sandstone outcrops that are harder, more resistant, and stand out in relief.
- Acid Test. Calcite reacts vigorously with dilute hydrochloric acid (HCl), producing effervescence (fizzing) due to the release of carbon dioxide gas. Apply a small drop to a suspected calcite area. Always wear appropriate safety gear (gloves, eye protection) when handling acids.
- Examine Vugs and Fractures. Calcite crystals are often best developed in open spaces such as vugs, geodes, or fractures within the sandstone, where they have room to grow.
- Check for Rhombohedral Cleavage. If the calcite is coarse-grained, look for its characteristic perfect rhombohedral cleavage, which distinguishes it from quartz or other common cementing minerals.
- Consider Geological Context. Calcite cementation is common in sandstones interbedded with or overlying limestones, or in areas with active groundwater flow through carbonate-rich rocks.
Quick Check
- Color:
- Variable (sandstone: white, gray, yellow, brown, red; calcite: colorless, white, yellow, brown, gray)
- Luster:
- Sandstone: dull to vitreous; Calcite: vitreous to sub-vitreous, sometimes pearly
- Streak:
- White (for calcite)
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