OPALISED FOSSIL PINEAPPLE

BLUE MAUVE 

One of the rarest and most fascinating types of opal comes in the shape of a palm-sized cluster of radiating points that resembles a pineapple. These "Opal Pineapples" are found only in the Cretaceous sediments of the White Cliffs in Australia

White Cliffs is the only place where these marvelous (and very rare) pseudomorphic “pineapple” opals have been found. They were formed when a mineral crystal of glauberite (or ikalite) was first replaced by calcite and then opalised.

Formula: SiO2•nH2O
Colour: Colorless, white, various
Hardness: 5½ - 6½

A pseudomorph (which means false shape in Latin) is a mineral that has replaced another mineral's chemistry or structure with its own without changing the outward shape of the original mineral while color, hardness, and other properties change to those of the replacing mineral. Transformations from one mineral to another are not unusual in nature, but preserving the outward shape of the original mineral is! The end result is that the crystal appears to be one mineral but is actually another.

Opal "Pineapples" - an opal pseudomorph formed by the replacement of glauberite by opal - found only in New South Wales.