Quartz vs Topaz
Quartz and Topaz are commonly confused, and 3 measured properties separate them — crystal system most clearly.
Quartz vs Topaz
Quartz
SiO2
The second most abundant mineral in the Earth's continental crust, and the reference point for hardness 7 on the Mohs scale.
Topaz
Al2SiO4(F,OH)2
Mohs 8, and the reason there is a step between quartz and corundum — a hard silicate whose main significance is as a reference point and a gemstone.
| Property | Quartz | Topaz |
|---|---|---|
| Cleavage Only one of the two has a figure we can stand behind, so there is nothing to compare. | Not known | perfect in one direction |
| Crystal system Categorical values can be listed side by side but not ordered or subtracted. | trigonal | orthorhombic |
| Density | 2.65–2.66 g/cm³ | 3.49–3.57 g/cm³ higher |
| 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. | 7 | 8 higher |
| Streak Categorical values can be listed side by side but not ordered or subtracted. | white | white |
Why these get confused
topaz is harder and has one perfect cleavage; quartz has none and breaks conchoidally
The confusion is a real and documented one, not a resemblance we have invented.