Calcite
“The backbone of limestone”
Mineral
Calcite is one of the most abundant minerals on Earth and the primary component of limestone and marble. It has a remarkable property called birefringence — transparent calcite crystals split light into two separate rays, producing a double image of anything viewed through them.
Composition
calcium carbonate (CaCO₃)
Where Found
Iceland (optical calcite), Mexico (giant crystals), England (chalk cliffs), worldwide in limestone regions
Mohs Hardness
3
Fun Fact
Vikings may have used transparent calcite crystals called 'sunstones' to navigate on cloudy days by detecting the sun's position through polarized light.
Test Your Knowledge
What optical property explains why objects viewed through a clear calcite crystal appear doubled?
Related Specimens
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