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Obsidian is formed by the rapid cooling of viscous lava due to volcanic explosions. It consists of the same minerals as granite, but cools so quickly that they do not have time to crystallize. Obsidian has a glassy luster and is usually black or a very dark green, but it can also be found in an almost colorless form.

Obsidian Polished
Obsidian Classification
Common Name Obsidian
Species Glass
Obsidian Optical Properties
Transparency Transparent - Opaque
Dispersion Strength: Weak Fire Value: 0.01
Refractive Index 1.490
Optic Character NA
Optic Sign NA
Polariscope Reaction Singly Refractive (SR) With ADR
Fluorescence SWUV: Inert
LWUV: Inert
Pleochroism None
Obsidian Characteristic Physical Properties
Hardness 5-5.5
Streak White
Specific Gravity 2.330-2.600 Typical:2.400
Toughness Varies
Inclusions Obsidian often has gas bubbles, cristobalite inclusions and stubby needle like inclusions. Banded obsidian: curved or sinuous bandsMacusanite: pale yellow to greenish obsidian from Peru. Mahogany obsidian: red and black banded material. Onyx obsidian: straight, parallel bandsSheen obsidian: silvery or golden looking sheen caused by gas bubbles Snowflake or flowering obsidian: white patches of cristobalite inclusions on a black backgroundRainbow obsidian: rainbow iridescent colors caused by numerous tiny bubblesApache tears: small, rounded irregularly shaped black nodules found in the American Southwest.
Luster Vitreous, Greasy
Fracture Conchoidal
Cleavage None
Obsidian Chemistry & Crystallography
Chemical Name silica
Chemical Formula SiO2(MgO,Fe3O4)
Crystal System NA

Obsidian Colors

  • Black Obsidian Black
  • Yellow Obsidian Yellow
  • Red Obsidian Red
  • Multi-color Obsidian Multi-color
  • Green Obsidian Green
  • Gray Obsidian Gray

Alternate Names

Banded Obsidian, Onyx Obsidian, Sheen Obsidian, Snowflake Obsidian, Rainbow Obsidian, Apache Tears

Countries of Origin

Argentina; United States of America (the); Unknown; Uruguay; China; Mexico; South Africa; Australia; Indonesia

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Tim Matthews is President and Chief Executive Officer of Jewelry Television® (JTV), as well as a member of the company's Board of Directors. He oversees and leads all aspects of the company's powerful omni-digital retail platform that uniquely specializes in fine jewelry and gemstones. His passion for business and gemstones has led him to become a recognized expert in the field of gemology. He is a life member of the Gemmological Association of Great Britain (Gem-A) and has earned Gem-A's highest degrees, the Gemmology (FGA) and Diamond (DGA) diplomas. He is also a Graduate Gemologist (GG) of the Gemological Institute of America (GIA) and has also completed GIA's Graduate Diplomas in Diamonds, Colored Stones and Pearls. Under his leadership, JTV has become the leader in the sourcing and selling of color gemstones and jewelry.

This page was created on June 27, 2014.

This page was last edited on October 24, 2019.