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.

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Image of opal mineral

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 button to switch between Metric and Imperial units.

Table of Opal Properties
Physical Properties
Metric
Chemical FormulaSiO2·nH2O
Crystal SystemAmorphous
Mohs Hardness5.5 - 6
Density1900 - 2200 kg/m3
ColorColorless, white, yellow, red, orange, green, brown, black, blue, pink
DiaphaneityOpaque, translucent, transparent
LusterSubvitreous to waxy
CleavageNone
FractureConchoidal to uneven
StreakWhite

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.