Impressive Opal “Pineapple” Pseudomorph after Glauberite. White Cliffs, New South Wales, Australia

A rare example of an opal pseudomorph after glauberite is this specimen known in the mineral hobby as a “pineapple”. The White Cliffs region of New South Wales, Australia is the only known locality for these specimens. Pseudomorphs are mineral specimens where one mineral has taken the form of a previously deposited mineral. While the process may sound simple, it is actually quite complicated. Some pseudomorphs are created when a second mineral grows over another, with the original dissolving away. Some are replaced molecule by molecule, or atom by atom, until the second mineral has the exact shape of the original mineral. In this case the glauberite crystals internally dissolved, leaving hollow pockets or cavities. Since glauberite forms in clay deposits, these environments enabled opal to form without interference or attachment of matrix or associates. Thus the specimen is terminated on all sides or is what is known as a “floating crystal”. Glauberite is now a rare mineral, but was once more prevalent as is evidence by the number of empty casts and pseudomorphs found in localities where little or no glauberite presently exists. In addition to being a mineralogical curiosity, the present opal “pineapple” is perhaps the finest we have seen—it exhibits a brilliant green in a very wide band across the center with strong play-of-color. Its “gemminess” is immediately apparent—for cutting quality opal to be seen in a pineapple is unheard of. A rare mineral specimen for the collector. Weighing approximately 816.0 carats and measuring 2 ¾ x 2 ¼ x 2in - Estimate: $35,000 - 40,000  (Copyright © 2002-2008 Bonhams 1793 Ltd., Images and Text All Rights Reserved)

Bonhams. Natural History, 22 Jun 2008. 220 San Bruno Street, San Francisco // 7601 Sunset Blvd., Los Angeles. www.bonhams.com