When mineral collectors hear Tasmania mentioned, they immediately think of crocoite, that rare mineral with vivid red-orange crystal needles, but crocoite gems are almost unknown.
The owner of the gem contacted me because he knew about my interest in unusual and rare Australian gemstones. Such gemstones are reference pieces for scientific study, have high educational value for public displays, and are of great interest to students (especially Gemmology students).
The Mineralogy Collection has a long history of strategic acquisitions of outstanding specimens, and this acquisition adds a unique and colourful, faceted 1.75 carat Tasmanian gemstone that is outstanding in its class.
Crocoite, a lead chromate of intense red-orange colour, is a rare mineral whose world’s best Australian locality is confined to only a few mines at Dundas, on the west coast of Tasmania. In fact, Tasmania declared crocoite its official State Mineral in 2000. Although too soft and brittle to wear as jewellery, a few rare crystals have been faceted over the years for collectors, so they, and similar gems are called ‘collector’s gemstones’.
Crocoite poses a significant challenge to gem cutters as a test of skill and the gem must be handled very carefully to avoid chipping or scratches or breakage along cleavage directions. Crocoite crystal needles are usually very thin and translucent to near-opaque, so to find crystals large enough to facet, free of internal flaws and of sufficient clarity, is rare indeed. The intense colour of crocoite, caused by the element chromium, cannot be adequately described (the name crocoite is from Greek and means ‘saffron orange’) but is instantly appealing, and its high lead content adds a bright sparkle.
The Museum has several outstanding specimens of crocoite crystal groups, the best on display in the 100 Treasures Exhibition in the Westpac Long Gallery, and others in the Chapman and Somerville collections, and in the general reference collection, so a crocoite gemstone enhances and adds interest to this selection.
This acquisition was made possible through a Grant from the Patricia Porritt Acquisition Fund through the Australian Museum Foundation. It fulfils a part of our gem collection strategy: that of acquiring rare and unusual gems facetted from minerals normally used as ores of metals (for example lead, zinc, tin and copper) and not usually found in gem form. It augments a set of such rare gems in our collection, with cerussite (lead carbonate), anglesite (lead sulfate), sphalerite (zinc sulfide), cassiterite (tin oxide) and cuprite (copper oxide).
It is hoped to display this set of unusual gemstones, including the crocoite, in a future mineral exhibition.
Collection Manager, Mineralogy and Petrology
- Bottrill, R.S. and W.E. Baker, 2008. A Catalogue of the Minerals of Tasmania, Tasmanian Geological Survey Bulletin 73, Mineral Resources Tasmania.