More recent work has shown that amethyst's coloration is due to ferric iron impurities. Further study has shown a complex interplay of iron and aluminium is responsible for the color.
On exposure to heat, amethyst generally becomes yellow, and much of the citrine, cairngorm, or yellow quartz of jewelry is said to be merely "burnt amethyst". Veins of amethystine quartz are apt to lose their color on the exposed outcrop
Synthetic amethyst is made to imitate the best quality amethyst. Its chemical and physical properties are so similar to that of natural amethyst that it can not be differentiated with absolute certainty without advanced gemological testing (which is often cost-prohibitive). There is one test based on "Brazil law twinning" (a form of quartz twinning where right and left hand quartz structures are combined in a single crystal) which can be used to identify synthetic amethyst rather easily. In theory however it is possible to create this material synthetically as well, but this type is not available in large quantities in the market. Composition
Amethyst is composed of an irregular superposition of alternate lamellae of right-handed and left-handed quartz. It has been shown that this structure may be due to mechanical stresses.
Because it has a hardness of seven on the Mohs scale, amethyst is suitable for use in jewelry.Hue and tone Amethyst occurs in primary hues from a light pinkish violet to a deep purple. Amethyst may exhibit one or both secondary hues, red and blue. The ideal grade is called "Deep Siberian" and has a primary purple hue of around 75–80%, 15–20% blue and (depending on the light source) red secondary hues.Green quartz is sometimes called green amethyst. Other names for green quartz are prasiolite, vermarine or lime citrine. History
Amethyst was used as a gemstone by the ancient Egyptians and was largely employed in antiquity for intaglio engraved gems.
The Greeks believed amethyst gems could prevent intoxication,while medieval European soldiers wore amethyst amulets as protection in battle – the reason for this being that amethysts are believed to heal people and keep them cool-headed.[citation needed] Beads of amethyst were found in Anglo-Saxon graves in England.
A large geode, or "amethyst-grotto", from near Santa Cruz in southern Brazil was presented at the 1902 exhibition in Düsseldorf, Germany. Amethyst is the traditional birthstone for February.
