History & Introduction
Obsidian occurs naturally by volcanic glass that is being used as a gemstone since
antiquity. Obsidian name came from Obsius, a Roman who actually found a similar
stone. The formation of obsidian occurs when lava cools and it looks like a mineral,
however because of its complex composition it is not considered to be a true mineral
and it lacks crystalline structure. Including to the decorative use, obsidian has
a practical use. With the absence of cleavage, conchoidal fracture with acute edges
after it is broken, even used to make smooth and sharp surgical scalpel blades.
From centuries ago obsidian are used to make arrow heads and blades, along with
ornaments by people in the pre-Columbian Mesoamericans and the ancient Egyptians.
The pure form of obsidian is in dark body colour because of iron and magnesium.
Obsidian is actually categorized in various kinds of characteristics. The basic
types of obsidian include the following: Mottled (snowflake and peanut obsidian),
banded or veined (Mahogany, midnight lace and pumpkin obsidian), pebbles or small
nodules (Apache tears) and sheen (cat's eye, sheen obsidian, rainbow and fire/flame
obsidian).
Recognizing - Obsidian is recognized as the glassy luster and single
refraction.
Availability - Obsidian is available to different areas in the
world that have experienced volcanic eruptions. Such places include Argentina, Georgia,
Canada, Armenia, Azerbaijan, Chile, Greece, El Salvador, Guatemala, Iceland, Italy,
Japan, Kenya, Peru, Mexico, New Zealand, Scotland, Turkey and the United States.
Usages - Cristobalite is used in scientific study. The crystals
give the basic information to how crystals form, and how they change over in different
environments.
Buying Guide
Color - Pure obsidian looks very dark and this is due to the presence
of iron and magnesium. Colourless obsidian is very rare to find. Mahogany obsidian
has dark-brown to black and red banding. Sheen obsidian is from dark-brown to black
by a golden or silver sheen (this is also called venturescence). Rainbow obsidian
is dark-brown to black with an iridescent sheen. Thus the iridescence of obsidian
can come in any colour blue, green, gold, silver, violet, or combinations of these
colours. Due to the presence of augitic pyroxene we have rainbow colors in rainbow
obsidian. Transparent pale yellow-green to brownish obsidian from Peru is referred
to as macusanite. Obsidian gemstone is available from translucent to opaque, black-streaked
orange, red or brown. The nodules from the American Southwest are famous as "Apache
tears". "Pumpkin obsidian" is another name for orange obsidian and plum-coloured
obsidian is called "plum obsidian".
Clarity and Lustre - Since obsidian is volcanic glass, it has a
vitreous (glassy lustre). It may include additions that cause a silver or gold sheen.
It even carry needle-like inclusions, gas bubbles, teardrop-shaped bubbles, torpedo-shaped
bubbles, or cristobalite crystal inclusions that look like "snowflakes" in "snowflake
obsidian". Obsidian available in Chile is found containing hardly any inclusions
of euhedral indialite crystals and transparent rods of sillimanite. Bolivian obsidian
contain orange spessartine inclusions. Obsidian can display chatoyancy (cat's eye
effect).
Cut and Shape - Due to the opacity of the maximum kinds of obsidian,
it is mainly in fancy cut, tumbled, cabochon cut, sphere-cut, made into cameos or
carved. Cabochon cuts shows the best presentation of any sheen or iridescence. Mainly
the materials that are translucent to transparent are faceted.
Treatment - Obsidian is generally not treated or improved in any
sort.
Gemological Characteristics: