Physical Properties¶
Hardness, specific gravity, cleavage, fracture, and lustre.
Interactive Version
For detailed data tables and interactive content, visit gemmology.dev/learn/physical-properties.
Hardness¶
Hardness measures a mineral's resistance to scratching. The Mohs scale ranks minerals from 1 (talc) to 10 (diamond).
| Hardness | Mineral | Common Gemstones |
|---|---|---|
| 10 | Diamond | Diamond |
| 9 | Corundum | Ruby, Sapphire |
| 8 | Topaz | Topaz, Spinel |
| 7 | Quartz | Amethyst, Tourmaline |
Practical Note
Gems with hardness <7 can be scratched by dust (quartz particles). Ring stones should ideally be hardness 7 or above.
Specific Gravity¶
Specific gravity is the ratio of a gem's density to that of water.
Formula: SG = Weight in air / (Weight in air - Weight in water)
Cleavage¶
Cleavage is the tendency of a mineral to break along flat planes related to its crystal structure.
| Quality | Description | Examples |
|---|---|---|
| Perfect | Very smooth surfaces | Topaz, Fluorite |
| Good | Relatively flat | Feldspar |
| Poor/None | No preferred direction | Quartz, Garnet |
Lustre¶
| Lustre | Description | Examples |
|---|---|---|
| Adamantine | Brilliant (RI >1.9) | Diamond, Zircon |
| Vitreous | Glass-like | Quartz, Beryl |
| Waxy | Like candle wax | Turquoise |
Data source: learn/physical-properties.yaml