Reference:

ABOUT OPALS

What is a Boulder Opal ?

Natural Opal Type 2 – is opal presented in one piece where the opal is naturally attached to the host rock in which it was formed and the host rock is of a different chemical composition. This opal is commonly known as boulder opal. (See figure 3B).

	Fig. 3B

Boulder opal

Usually thin layer of precious opal naturally adhering to brown ironstone host rock. Relatively abundant

Queensland opal fields

Find more information at the OPAL Association's Opal Nomenclature Section of their Website:

http://www.opal.asn.au/information_nom