Quartz vs. Calcite: How to Tell the Difference
They might look similar to the untrained eye, but these two common white minerals are actually very different. Here is how to tell them apart.
The Hardness Test
Quartz is significantly harder than calcite. Quartz (hardness 7) will scratch glass, while calcite (hardness 3) will not. In fact, a copper penny can scratch calcite but won't leave a mark on quartz.
The Acid Test
Calcite is a carbonate mineral, meaning it reacts to acid. If you place a drop of weak acid (like vinegar) on calcite, it will bubble and fizz. Quartz will not react at all.
Cleavage and Fracture
Calcite breaks along distinct flat planes (cleavage), often forming rhombohedrons. Quartz has no cleavage and breaks with a curved, glass-like fracture (conchoidal fracture).
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