The story of diamonds in Western Australia
Article | Updated 6 months ago
Pink and yellow treasures from the deep
Precious, brilliant and hard – diamonds have fascinated us since time immemorial. Over time scientific investigation has revealed their origins, even if some mysteries remain…
Diamonds are rarities of nature wrought by precise rules of chemistry. Most diamonds formed deep in the Earth, where they may have been stored for millions of years, before being carried to the surface in rapidly ascending streams of molten volcanic rock.
Diamond is the high-pressure form of carbon and generally crystallises at depths greater than 150km below the Earth’s surface. Compared to the radius of the Earth, which is about 6400km, this zone of diamond formation is still quite close to the surface! At these depths, the temperature increases substantially and diamonds form at about 900 to 1400 degrees Celsius.
Diamonds found at the Earth’s surface generally crystallised in areas of the mantle beneath regions of ancient, stable continental crust. In the prolific Argyle diamond mine most of the diamonds probably formed around 1.5 billion years ago. Rapid volcanic transport from their source rocks in the Earth’s mantle to the surface ensures that diamonds don’t transform to the common low-pressure form of carbon, the much less valuable graphite, which we use in our pencils.
The Kimberley region, in northern Western Australia, has been a prolific source of diamonds since the 1980s. Western Australia is particularly famous for its production of coloured diamonds and has become the primary source of pink diamonds for the world’s markets.
The Argyle mine in the east Kimberley produces diamonds that range in colour from white (colourless), through yellow and brown (now called ‘champagne’ and ‘cognac’), to rare pinks and blues. Deformations and defects in the atomic structure of pink diamonds in combination with a peculiar arrangement of trace amounts of nickel and nitrogen are the probable source of their colour.
Over in the west Kimberley, the Ellendale mine presently contributes approximately 50% of the world production of high-quality fancy yellow diamonds. Yellow colours in the Ellendale diamonds are produced by their nitrogen content, where nitrogen atoms selectively absorb light in the blue region of the visible spectrum meaning that the diamonds appear yellow.
To gain a greater appreciation of diamonds from Western Australia you can visit the ‘Diamonds to Dinosaurs’ gallery at the Western Australia Museum in Perth, where valuable pink and yellow diamonds are displayed.
Learn more about the pink and yellow diamonds of Western Australia by watching a talk given by Peter Downes, a Curator in Minerals and Meteorites at the Western Australian Museum.
Find out more information about diamonds on the website of the Geoscience department of Australian Government.
For further information about the current knowledge on diamonds you also can visit the website of the Gemological Institute of America (GIA).
Find out more information about the Ellendale diamond collection here.