Where is Calcite found?
CaCO3
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Open the appCalcite 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
Carlsbad Caverns, New Mexico, USA
Famous for spectacular speleothems (stalactites, stalagmites, flowstone) composed primarily of calcite.
Iceland
Historically known for 'Iceland Spar,' a transparent, high-purity calcite exhibiting strong birefringence.
Mexico
Various localities produce large, well-formed calcite crystals, often in diverse habits and colors.
Missouri, USA
Known for lead-zinc mining districts where calcite is a common gangue mineral, often forming large, clear crystals.
Worldwide Limestone and Marble Quarries
Calcite is the primary mineral in these rocks, found in vast quantities globally.
Collecting tips
- Acid Test. Calcite effervesces vigorously (produces bubbles of CO2 gas) when a drop of dilute hydrochloric acid (HCl) is applied to its surface. This is a definitive test to distinguish it from similar minerals like dolomite (which reacts weakly or not at all unless powdered) or gypsum (which does not react).
- Cleavage Recognition. Look for the characteristic perfect rhombohedral cleavage. Even in massive forms, small cleavage fragments will exhibit this shape. This helps differentiate it from quartz or feldspar.
- Hardness Test. Calcite has a Mohs hardness of 3, meaning it can be scratched by a copper coin (hardness ~3.5) but will scratch a fingernail (hardness ~2.5). This helps distinguish it from harder minerals like quartz (7) or softer ones like talc (1).
- Double Refraction (Birefringence). Transparent calcite, especially in thicker pieces, will exhibit strong double refraction. If you place a clear piece of calcite over text, the text will appear doubled. This is a key optical property.
Quick Check
- Color:
- White, colorless, or various tints
- Luster:
- Vitreous to pearly
- Streak:
- White
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