Wild Horse

The photo shows three polished stones: an oval one, with white patches surrounded by a fine web of brown and grey lines, and two rectangular ones, with large cream areas and reddish brown patches. "Wild Horse" is not a mineral name but a trade name. According to Enchanting Earth and FossilEra, it is a natural combination of magnesite, a white mineral, and hematite, an iron oxide that gives the reddish brown. According to Rincon Trading, the name comes from the brown and white patterns, which resemble the wild horses of the American West.

It is sometimes sold as "Wild Horse turquoise", but there is no turquoise in it. So why turquoise? According to Geology.com, white magnesite cabochons with a grey, black or brownish "matrix" remind people of turquoise, so they are sometimes called "white turquoise", which is a misnomer. And there is a less innocent side: white magnesite is porous and absorbs dye easily, and according to Geology.com, for nearly 100 years it has been dyed blue and sold as a turquoise substitute, sometimes disclosed and sometimes not. Our stones stayed white and brown, and did not try to pass as anyone else.

According to FossilEra, Wild Horse comes from near the Globe copper mine in southeastern Arizona. According to the site, it forms through low-grade metamorphism, at 200 to 320 °C and low pressure, when magnesium-rich rock meets a carbonate-rich solution. The result is a rock with white magnesite plumes set in a reddish brown, hematite-rich matrix. According to Enchanting Earth, it comes from a single area only, so the pieces are usually small.

It is worth knowing that it is soft. According to Geology.com, magnesite has a hardness of 3.5 to 5, and according to Enchanting Earth, Wild Horse is 3.5 to 4.5. That is much softer than quartz, so it is best taken off before a gym session, and kept away from harder stones.

And finally, some family perspective. According to Geology.com, most magnesite in the world never becomes jewelry: it is heated to make magnesium oxide, which is used mainly for heat-resistant bricks that line kilns and blast furnaces. So while its relatives work in the furnace, Wild Horse poses on white fabric.