#mienral

My Collection

The Argyle Pink Jubilee

The most consistent source of pink, purple and the very rare red diamonds is the Argyle mine in the remote desert wastes of Western Australia (seehttps://www.facebook.com/TheEarthStory/posts/516555285072187), and the annual tenders in Perth are one of the fixtures of the high end jewellery market since these special stones are usually cut in house so as to maximise the added value. There are only ever a few stones for sale over a carat, maybe half a dozen yearly. The largest rough pink ever found there (in 26 years ofoperation) is this slightly etched distorted octahedron, which weighed in at a puny 12.76 carats (2.552 grams). The colour is a pale but powerful rose, similar to the Williamson Pink, found in Tanzania and gifted to the Queen of England on theoccasion of her wedding by the mine owner. Unlike most of the mine's production, this stone ended up being donated to the Melbourne museum (where it on permanent display) after being the expected star of the show at an invitation only tender in 2012. Luckily for the world, when they started cutting it they found a knot, an internal line of stress and incipient cleavage reflecting the stone's exciting geological history during the process of formation or eruption from the mantle in the lamproite pipe that brought it to the surface (these knots are known in the trade as a gletz). When the saw or scaithe (the round polishing disc) encounter these knots, the usual result is that the stone promptly explodes into shards as the internal strain is released.

The preshaping removed 4 carats (it is common to lose 40-80% of a rough diamond during cutting) before it was donated to the museum, but pieces like this almost never end up in such places in the rough. Rich patrons sometimes donate cut stones, such as the Hope at the Smithsonian, but commercial companies tend to sell all their rough. While they could have cut several smaller stones out of the rough, it was decided to donate it, since it had been the largest Argyle crystal ever found. Since the museum had a long standing relationship with Rio Tinto, they got the lucky prize. Next time I'm over that way I guess I'll drop round and visit it.

Loz

From the “Sweethome mine”, Colorado, USA. Insanely rich red Rhodochrosite. Insanely hard to cut (Mohs 4). The cutter won an award for it, but subsequently died. It’s part of the Somewhere In The Rainbow collection. ❤️ Thanks to Craig Lynch at the #tucsongemshow

Cronstedtite

Mantle minerals occasionally make it up towards the surface, including as obducted chunks of oceanic crust shoved up onto continents during mountain building events where the remnants of oceans past are called ophiolites (see http://bit.ly/2A8LpMJ). As these rocks are exposed to percolating waters in the crust the usual mantle minerals such as olivine (see http://bit.ly/2AbnsV4) start to alter into others, usually hydrous, of which the serpentine family is the most common (see http://bit.ly/2Bg1a1h and http://bit.ly/2jqn5vq). The mineral in the photo is one of this family, discovered in 1821 and named after a Swedish mineralogist who discovered nickel and Scheelite (see http://bit.ly/2vlH4AR) whose textbooks revolutionised the subject. Little known these days he was hailed as one of the fathers of mineralogy

It shows up as the product of hydrothermal alteration in veins. Colour varies from black through greeny black to dark brown and the Mohs hardness is 3.5. Locations include Peru (where this 5.2 x 4.1 x 2.2 cm specimen of iron silicate sitting atop the iron carbonate siderite with associated pyrite was mined) , Romania, France, Brazil Bohemia in the Check Republic and Cornwall in England though it has also turned up off planet, in the class of meteorites that have been altered by water out there in the depths of spacetime known as CM chondrites.

Loz

Image credit: Rob Lavinsky/iRocks.com

BB-M-0431

24x16x15mm / 21g (Thumbnail)