Calcite vs Quartz
Calcite and Quartz are commonly confused, and 2 measured properties separate them — density most clearly.
Calcite vs Quartz
Calcite
CaCO3
Calcium carbonate — the mineral of limestone, marble, chalk and most shells, and the reference point for hardness 3.
Quartz
SiO2
The second most abundant mineral in the Earth's continental crust, and the reference point for hardness 7 on the Mohs scale.
| Property | Calcite | Quartz |
|---|---|---|
| Cleavage Only one of the two has a figure we can stand behind, so there is nothing to compare. | perfect rhombohedral in three directions | Not known |
| Crystal system Categorical values can be listed side by side but not ordered or subtracted. | trigonal | trigonal |
| Density | 2.71–2.72 g/cm³ higher | 2.65–2.66 g/cm³ |
| Lustre Categorical values can be listed side by side but not ordered or subtracted. | vitreous | vitreous |
| Mohs hardness Mohs hardness is an ordinal scale: values can be ranked, but differences and ratios between them are not meaningful. | 3 | 7 higher |
| Streak Categorical values can be listed side by side but not ordered or subtracted. | white | white |
Why these get confused
both common, colourless and vitreous; separated instantly by hardness and by acid
The confusion is a real and documented one, not a resemblance we have invented.