Amethyst

VARIETY INFORMATION:

• Variety of: Quartz , SiO2 .
• Uses: Gemstones and ornamental stones.
• Birthstone for: February
• Color: various shades of purple.
• Index of refraction: 1.544-1.553
• Birefringence: 0.009
• Hardness: 7
• Cleavage: none
• Crystal system: trigonal
• Pleochroic: no 

Amethyst is the purple variety of quartz and is a popular gemstone. If it were not for its widespread availability, amethyst would be very expensive. The name "amethyst" comes from the Greek and means "not drunken." This was maybe due to a belief that amethyst would ward off the effects of alcohol, but most likely the Greeks were referring to the almost wine-like color of some stones that they may have encountered. Its color is unparalleled, and even other, more expensive purple gemstones are often compared to its color and beauty. Although it must always be purple to be amethyst, it can and does have a wide range of purple shades.

Amethyst can occur as long prismatic crystals that have a six sided pyramid at either end or can form as druzes that are crystalline crusts that only show the pointed terminations. As a mineral specimen, amethyst is popular for its color and nice crystal shapes that produce a handsome, purple, sparkling cluster.

However, amethyst is not the same everywhere. Different localities can produce a unique amethyst to that particular region or even to that particular mine. Experts can often identify the source mine that a particular amethyst came from. The key to this is the specimen's color, shape of crystal, inclusions, associations and character of formation.

The following is a list of many of the more noteworthy localities and some of the attributes that characterize the amethyst found there.

• Vera Cruz, Mexico  very pale, clear, prismatic crystals that are sometimes double terminated and have grown on a light colored host rock. Crystals are typically phantomed, having a clear quartz interior and an amethyst exterior. Some are sceptered and phantomed.
  
• Guerrero, Mexico  dark, deep purple, prismatic crystals that radiate outward from a common attachment point. Often the crystals are phantomed opposite of Vera Cruz amethyst having a purple interior with a clear or white quartz exterior. These are some of the most valuable amethysts in the world.
  
• Minas Gerais and Rio Grande do Sul, Bahaia, Brazil  crystals form in druzy crusts that line the inside of sometimes large volcanic rock pockets (vugs) called geodes. Some of the vugs form from trees that were engulfed in a lava or volcanic ash flow millions of years ago and have since withered away. Other vugs are just gas bubbles in the lava. Some vugs can be quite large. The crystals that form are usually light to medium in color and only colored at the tops of the crystals. Most clusters form with gray, white and blue agate and have a green exterior on the geodes. Calcite sometimes is associated and inclusions of cacoxenite are common. More rarely, gypsum crystals adorn the amethyst.
  
• Maraba, Brazil  large crystals with unattractive surfaces that are of a pale to medium color and often carved or cut into slices.
  
• Thunder Bay, Canada  a distinct red hematite inclusion just below the surface of the crystals is unique to this locality. Clusters are druzy crusts that line the fissures formed in ancient metamorphic rocks.
  
• Uruguay  crystals are dark to medium and form in druzy crusts that line the inside of volcanic vugs that have a gray or brown exterior. The crystals are usually colored throughout, unlike the Brazilian crystals, and form with a multicolored agate that often contains reds, yellows and oranges. Often amethyst- coated stalactites and other unusual formations occur inside these vugs.
  
• Africa  crystals are usually large but not attractive. However, the interior color and clarity are excellent and polished slices and carvings as well as many gemstones are prized and admired.
  
• Maine, USA  Dark druzy clusters that are not widely distributed today.
  
• North Carolina, USA  Druzy clusters that have a bluish-violet tint.
  
• Pennsylvania, USA  druzy clusters that filled fractures in metamorphic rocks. They are generally a brownish purple and patchy in color.
  
• Colorado, USA  druzy clusters form crusts inside of fissures in sandstone, often on top of a crust of green fluorite. Crystals are dark but rather small.
  
• Italy  both Vera Cruz like crystals, although not as well defined, and large parallel growth clusters with good evenly distributed color.
  
• Germany  associated with colorful agates that form a druzy light-colored crust.
• Ural Mountains, Russia  a very clear and dark variety that is cut for fine expensive gemstones, natural uncut clusters are rarely on the market.

 

Often cut gems of amethyst are graded using the terms: Siberian, Uruguayan or Bahain; to represent high medium and low grade respectively, regardless of the actual source. Because of the patchyness of the color distribution in the crystals, Amethyst is often cut as brilliant round cuts to maximize the color. Other cuts can be used when the color is better distributed.

The color purple is traditionally the color of royalty and amethyst has been used since the dawn of history to adorn the rich and powerful monarchs and rulers. Today, amethyst is a lovely and affordable gemstone that is fortunately available in a wide variety of cut and uncut stones that we can all possess and admire.

Amethyst is only one of several quartz varieties. Other varieties that form macroscopic (large enough to see) crystals are as follows:

• Citrine is a yellow to orange gemstone variety that is rare in nature but is often created by heating Amethyst.
• Milky Quartz is the cloudy white variety.
• Prasiolite is the leek-green variety, rare in nature but used as a gemstone, sometimes (wrongly) called Green Amethyst.
• Rock crystal is the clear variety that is also used as a gemstone.
• Rose quartz is a pink to reddish pink variety.
• Smoky quartz is the brown to gray variety.