Calcite vs Precious coral
Calcite and Precious coral are commonly confused, and 2 measured properties separate them — density most clearly.
Calcite vs Precious coral
These are different kinds of thing (mineral, material). Fewer properties mean the same thing across both, so a like-for-like reading may not be available.
Calcite
CaCO3
Calcium carbonate — the mineral of limestone, marble, chalk and most shells, and the reference point for hardness 3.
Precious coral
The skeleton of a deep-water colonial animal, red because of a carotenoid rather than a metal — and slow-growing enough that the trade has outrun it repeatedly.
| Property | Calcite | Precious coral |
|---|---|---|
| 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 Only one of the two has a figure we can stand behind, so there is nothing to compare. | trigonal | Not known |
| Density | 2.71–2.72 g/cm³ higher | 2.6–2.7 g/cm³ |
| Lustre Only one of the two has a figure we can stand behind, so there is nothing to compare. | vitreous | Not known |
| Mohs hardness Mohs hardness is an ordinal scale: values can be ranked, but differences and ratios between them are not meaningful. | 3 | 3–4 higher |
| Streak Only one of the two has a figure we can stand behind, so there is nothing to compare. | white | Not known |
Why these get confused
dyed calcite and dyed howlite are sold as coral constantly; real coral shows the fine longitudinal growth striations of a branch, and dyed stone shows colour concentrated in cracks
The confusion is a real and documented one, not a resemblance we have invented.