Opal is a hydrated amorphous form of silica; its water content may range from 3 to 21% by weight but is usually between 6 and 10%. Because of its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are classed as minerals. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock. Opal is softer and more easily chipped than most other popular gemstones. It has a hardness of about 5.5 to 6.0 on the Mohs hardness scale.

Pink opal veins range in thickness from half a centimeter to a maximum of 6 cm, most commonly at around 1 to 2 cm of thickness. Pink opal ranges in color from nearly white, through carnation pink, through lilac, with the latter being the rarest and most expensive quality. High-quality pink opal rough stone does sell for up to 2000 $US per kilo and is of course only used for jewelry.