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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:

Chemical Formula 70-75% SiO2 + MgO, Fe3O4 Volcanic, amorphous, siliceous glassy rock
Crystal Structure None
Colour Black, grey, brown, orange; rarely red, blue or green
Hardness 5 - 5.5
Refractive Index 1.45 - 1.55
Density 2.35 - 2.60
Cleavage Not available
Transparency Transparent to opaque
Double Refraction or Birefringence Not present
Lustre Vitreous
Fluorescence None
Crystal System Tetragonal
Tenacity Brittle
Rock Type Igneous
Popularity (1-4) 3
Prevalence (1-3) 2
Demand (1-3) 2
Fracture Conchoidal
Environment Cristobalite occurs in igneous rocks located in areas of volcanic activity, often lining gas bubbles in the host rock.

Classification:

  • White obsidian
  • Light gray obsidian
  • Yellow obsidian
  • Light brown obsidian
  • Blue gray obsidian