Properties of Opal
Opal is a type of mineral composed of silica spheres that diffract light, creating a play of colors known as “opalescence.” This gemstone is valued for its unique iridescence, which can display a vibrant spectrum of colors.
The following table provides a comprehensive list of opal properties in both SI and US customary/Imperial units at normal temperature and pressure (NTP).
Note: click on the icon to switch between Metric and Imperial units.
| Physical Properties | Metric |
|---|---|
| Chemical Formula | SiO2·nH2O |
| Crystal System | Amorphous |
| Mohs Hardness | 5.5 - 6 |
| Density | 1900 - 2200 kg/m3 |
| Color | Colorless, white, yellow, red, orange, green, brown, black, blue, pink |
| Diaphaneity | Opaque, translucent, transparent |
| Luster | Subvitreous to waxy |
| Cleavage | None |
| Fracture | Conchoidal to uneven |
| Streak | White |
Note: unless stated otherwise, all values are taken at room temperature (approximately 20°C or 68°F) and 1 atm pressure. (1 atm = 101,325 Pa)
Related Pages
References: 1) Cardarelli, François. Materials Handbook: A Concise Desktop Reference. Switzerland: Springer International Publishing, 2018. 2) CRC Handbook of Chemistry and Physics, 97th Edition. United Kingdom: CRC Press, 2016-2017.