Description
Ametrine, also known as trystine or by its trade name bolivianite, is a naturally occurring variety of quartz. It is a mixture of amethyst and citrine with zones of purple and yellow or orange. Almost all commercially available ametrine is mined in Bolivia, but deposits in Brazil and India are exploited. The color of the zones visible in ametrine are due to the different oxidation states of iron within the crystal. These different oxidation states occur due to a temperature gradient across the crystal during its formation. Artificial ametrine can be created by differential heat treatment of amethyst. Legend has it that ametrine was first introduced to Europe by a conquistador's gifts to the Spanish queen after he had a mine in Bolivia as a dowry when he married a princess from the indigenous Ayoreos tribe. Most ametrine in the low-priced range can be assumed to originate from synthetic material. Since 1994, a Russian laboratory has perfected the industrial production of two-tone quartz crystals, which are then irradiated to produce the characteristic ametrine colors. Green-yellow or gold-blue ametrine does not occur naturally.
Amethyst is a violet variety of the mineral quartz (SiO2) and is the most sought-after stone of the quartz group. Etymology: The name derives from the Greek αμεθυστoς (amethystos). Amethyst was already known to the Egyptians, Etruscans, and Romans, and was described by Pliny the Elder. In ancient China, small gems were cut from amethyst. In the Middle Ages, amethyst was also highly prized in Europe. It was called the bishop's stone because it was once a favored gemstone for ecclesiastical dignitaries and was believed to possess magical powers. It was the symbol of lovers, the stone of temperance, a protector against sorcery and witchcraft. Jacob van Maerlant offers an explanation that the stone dispels drunkenness. It has been assumed that the Greek name meant "against intoxication": wine drunk from a cup made of amethyst was said to prevent one from becoming drunk. Origin: Metamorphic, hydrothermal, alluvial deposits. The crystals always grow on a substrate; the prisms are often weakly developed, and therefore the crystal points of amethyst predominate; here, the color is also most intense. These parts are knocked off, that is, broken off for further use. Firing at temperatures between 470 and 750 degrees Celsius produces light yellow, reddish-brown, green, or colorless varieties. Some amethysts gradually fade in daylight. Radium irradiation can restore the original color. The color is caused by iron combined with ionizing radiation. Amethyst is less attractive in artificial light. Occurrence: As early as the Middle Ages, Brazil boasted its amethyst deposits; they are mined in places including Bahia, Minas Gerais, and Mato Grosso. Recently, the so-called ametrine, an amethyst-citrine, has been mined in Bolivia, where the violet and yellow colors alternate, but the transition between the colors is sharply defined. Amethysts are also known in the United States, namely in Montana, Maine, Georgia, and Arizona. Canada, Mexico, Bolivia, India, Myanmar, Japan, China, and Korea, as well as Sri Lanka, Zimbabwe, Congo, and Australia, are also important producers. In Russia, amethyst is found in the Urals, Yakutsk, and the Kola Peninsula, among other places. Amethysts are also found in Armenia, Germany, the Czech Republic, Slovakia, Bulgaria, Switzerland, and Ireland. Amethyst rarely forms larger, pure crystals. The British Museum houses a unique cut stone weighing 343 carats. Other, smaller stones weigh less; they usually come from Brazil. The Smithsonian Institution in Washington, DC, even possesses a cut amethyst from Brazil weighing 1,362 carats and one from North Carolina weighing 202.5 carats. Amethysts were often used in state jewels, such as Catherine the Great's scepter and the scepter of the British Crown.
