A gorgeous natural mixture of amethyst and citrine, this beautiful name can hardly say its been used at all - in fact there are likely as few as two people in the U.S. named Trystine. While the stone itself is known as ametrine (amethyst + citrine as a smush word) or golden amethyst, it is naturally found in Bolivia, thus the trade-name is Bolivianite. There are several varieties of quartz, including onyx, Tiger's eye, rock crystal, and amethyst and citrine individually.
To be clear, a gemstone is a "mineral crystal" and it can be a precious or semi-precious stone. When cut and polished these are used to make jewelry. A few gemstones are not minerals at all, such as lapis lazuli, amber and jet.
In legend, ametrine was first seen when a Conquistador inherited a Bolivian mine via marriage to a Princess Anahi of the Ayoreos tribe, and he gifted some of these New World gemstones to the Queen of Spain. This must only be legend because the Ayoreo were supposedly first contacted by Jesuits in the 1720's, but that is not to say a similar situation could've never happened. Most ametrine sold today is lab-created. You can read more about the legend at the stone's official website, www.ametrine.com Also be sure to check out anahite, also found at this mine, and also very beautiful.
The name Trystine, which means "thrice" or "three" is in reference to a cutting process: when a gemstone has alternating color segments and is cut perpendicular to its c-axis, a pinwheel shape is visible, and in ametrine it will have 3 violet and 3 yellow sectors when cut perfectly. That information is found here and to be honest I think you have to be a mineralogist/geologist/jeweler to understand it, but that is the only clue as to how ametrine also became known as trystine. There is no one to credit with naming it and no other backstory.
In 2015 there were 6 girls given the name Tristine.