Abstract Gems & Gemology, Spring 2013, Vol. 49, No. 1

Major Crocoite Discoveries at the Adelaide Mine, Tasmania

Crocoite, first discovered in the Urals in 1766, was named crocoise in 1832. Its attractive orange-red hue and adamantine to vitreous luster make it one of the most pursued mineral collector specimens. Tasmania, located southeast of mainland Australia, has long been famous for its outstanding crocoite specimens, and nearly all commercial specimens come from the Red Lead and Adelaide mines.

The mines lie within a four-square-kilometer area. Cambrian intrusions of serpentinite within the Precambrian and slightly younger metasedimentary rocks provided the Cr needed to form crocoite. During the Devonian, metal-rich granitic intrusions provided hydrothermal fluids along the extensive shear zones to alter much of the serpentinite to a peculiar rock called listwanite and precipitate pods with veins of Pb-bearing minerals. Since crocoite is more stable than other Pb-bearing minerals at low pH levels, it predominated in these mines. Crocoite was common in the gossan, but open pockets yielded the best samples.

The earliest discovery of crocoite in Tasmania dates back to 1891. Over the last 120 years, it has been mined intermittently at several localities. Until the 1970s, many of the high-quality specimens were either destroyed or used for industrial applications. In 1970, “crocoite king” Frank Mihajlowits leased the Adelaide mine and began a string of major discoveries. Among these was a watercourse discovered in 1990 that was worked on for 14 years and yielded thousands of superb specimens.

In 2004, Mihajlowits sold the mine to Adam Wright’s newly established Adelaide Mining Company, which continues to work the deposit. A major new pocket of crocoite found in 2012 was of great excitement to mineral collectors. The opening of this watercourse is about one meter wide and two meters tall. Crocoite crystals of various lengths protrude at different angles to each other. This discovery is called the “Red River find,” and the watercourse has been broken into from below with no end to the channel found as yet. Many of these superb specimens were exhibited at the 2012 Tucson show.

Abstracted by Tao Hsu