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 or "vugs". Some of the vugs form from trees that were
engulfed in a lava 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 vugs. Calcite sometimes is associated
and inclusions of cacoxenite are common.
- 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 patchiness 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.
Serendipity
Ranch Gem Mine