Total Pageviews

Monday, February 27, 2012

Ametrine the Astounding Bicolored Stone

A faceted example of ametrine
Photo by De Wela49

Ametrine is a variety of colored quartz where one end of the crystal is amethyst colored and the other end is citrine colored. Most of these stones are found in Bolivia and are often marketed under the name bolivinite. Because they are fairly abundant they are not considered to be an expensive gem. Many of these stones today are actually synthetics made in Russia.

In 1994 a Russian chemist perfected a method to make multicolored quartz crystals in a pressurized vessel. These stones are later subjected to radiation that brings out the typical Ametrine colors. It is easy to detect these stones because in nature neither yellow-green nor gold-blue exists. In nature but artificial ametrine can also be created by treating an amethyst crystal on one end with heat. Since quartz is a poor conductor of heat only one end of the crystal that has been heated will change color.

An example of ametrine from Bolivia.
Photo by Ra'ike 

The most probable cause of a bi-colored amethyst crystal is by differential heat that is applied to one end of the crystal; in the case of Bolivianite causing a temperature differential across the length of the crystal will create a bi-colored stone.

Most of the Ametrine enters into trade comes from a single mine in Bolivia although there are some other places that produce the same gem notably Brazil and India. There are several legends concerning the Bolivian mine the most prevalent being the one about a Spanish Conquistador who presented them to the Spanish Queen as a present after he had learned about the Anahi mine where they were produced as a dowry present to Mary by an Indian princess named Anahi from the Ayereos tribe.

An ametrine crystal also from Bolivia
Photo by Rob Lavinsky

Typically Ametrine is faceted into a rectangular shape with a 50-50 combination of amethyst and citrine showing its bicolor nature. There are times when there is a checkerboard pattern of facets that is added to the top of the stone to increase the natural light reflection. This stone can also be cut in such a way as to blend the two colors creating a mixture of yellow, purple, and peach tones in the stone. Ametrine is also a popular stone among artistic cutters and carvers that like to play with the various colors creating landscapes from the stone.

When buying one of these stones the buyer has to remember that at a Moh’s hardness of 7 it is not a particularly durable stone that should not be used in rings that are going to be worn steadily. This tone is more suitable for broaches and pendants. You can buy this stone in just about any size or shape but remember the color contrast stands out better in stones over seven carats in size.

1 comment:

  1. Excellent, John. I did not know you could create this characteristic using heat. I'll have to try that sometime!