"This beautiful specimen was found at... "Kens Retreat" in the Coocoran mining area N/West of Lightning Ridge..."Text and image from Opal Auctions, via Bijoux et Mineraux.
The centre of Australia used to be an inland sea. Miners now unearth opalized fossils from its hot dry deserts. Opalized fossils include vegetation or wood from Boulder Fields and opalized clam shells from Coober Pedy.
Opalized fossils also include sea shells, teeth, and even opalised belemnites (squid). Opalised shells with good colour and small amounts of potch are hard to find, and many are worth more if left natural and unpolished. Among the rarest are opalized pineapple, found only in White Cliffs Opal Fields."