Opal formula is SIO2 H2O. There are different varities of Opals. 

  1. Precious Opals
  2. Fire Opals
  3. Boulder Opal
  4. Non Iridescent Opals

Precious Opals

Precious opals have beautiful iridesecent phenomena. Their main body is white to black body colour. Usually they come also in transparent to opaque. 

Opal Gemstones  

Fire Opal

Fire opal colour goes from brown to orange. They may be iridescent. 

Transparency: Transparent to opaque

Luaster: Sub vitreous

R.I. 1.40 to 1.45 

S.G: 2.2 

Boulder Opals

These are also iridescent opal in brown rocks.The stone will have mother rock in brown form.

Non Iridescent Opals

Thhere are also opals that does not show play of colours. They come in different colours such as green, pink, blue, brown.

Opal gemstones