Australian Marlborough Chrysoprase. Gem cut by Ryan Quantz. http://www.greengemfoundation.com/gemstones/australian-marlborough-chrysoprase/
This gem is one I stumbled across a while ago and was taken back by its simple beauty. Chrysoprase is a rare form of quartz and composed of microscopic crystals of SiO2, with the apple green color coming from nickel oxide. It is fairly durable at around 7 Mohs, and looks stunning in both gold and silver settings.
Chrysoprase adorned the ancient Egyptians, Greeks, and Romans (though scholars are unsure where they got the stones), and found its way into medieval churches. Its unique name comes from the Greek words chrysos, meaning “gold,” and prasinon, meaning “green.” There is a fabled prase stone worn by Alexander the Great that granted him victory in battle for eleven years. He had it until a snake bit the girdle it was in and the gem fell into the Euphrates (either while Alexander was wearing it or as he had left it by the shore to bathe in the river, depending on the version). It caused him to lose his winning streak, and made chrysoprase synonymous with good fortune. In China, the stone is still used in medicine to balance Chi, and in India, it is said to be able to heal a broken heart.
Rough Marlborough Mine chrysoprase. Image by Yvonne Jiew at http://www.rockandmineralsupermarketaustralia.com/
The material from Australia is generally considered superior for its color and translucency, but chrysoprase is also found in locations across Europe, Russia, Brazil, and Arizona. It was mined as early as the 14th century in Frankenstein, Poland and loved by Prussian royalty, but the local deposits were depleted long ago. As good material is becoming increasingly hard to come by and as other types of chalcedony are routinely fabricated, there are many false stones out there. There is also speculation that Australian material is being exported and sold as Chinese Jade, which is also rare and valuable, but all of these things can be easily distinguished by a trained gemologist.