Obsidian

Big Photo

Mahogany Obsidian
Indonesia
69.01 carats
© gemselect.com

Obsidian was so named from its resemblance to a stone found in Ethiopia by Obsius. It was used in antiquity for amulets and necklaces.

Obsidian is a naturally occurring volcanic glass. It is usually an opaque black or grey but may be yellow, red, greenish brown. Obsidian may have an iridescent sheen caused by inclusions.

Obsidian is used for ornamental purposes and as a gemstone.

Many colored glasses are sold as "obsidian" often claiming to be natural.

Obsidian Gemstones by Colour

This table shows the variety of hues this gemstone can be found in. Click on a photo for more information.
 
 
 

Obsidian Gemstones by Size

This table shows distribution of Obsidian gemstone sizes that are listed on this site. This can give a good indication as to the general availability of this gemstone in different sizes.
Contributed photos
Lightest:0.16 cts
Heaviest:168.6 cts
Average:34.77 cts
Total photos:33
Do you have a larger Obsidian? Why not upload a photo?
0.16ct to 17.00ct17.00ct to 33.85ct33.85ct to 50.69ct50.69ct to 67.54ct67.54ct to 84.38ct84.38ct to 101.22ct101.22ct to 118.07ct118.07ct to 134.91ct134.91ct to 151.76ct151.76ct to 168.60ct
General Information
A variety or type of:Glass
Varieties/Types:
Apache Tears - Small rounded pebbles of black Obsidian found in American Southwest.
Mahogany Obsidian - A variety of Obsidian with black and red banding.
Rainbow Obsidian - Obsidian with multicolored iridescence.
Sheen Obsidian - A variety of obsidian exhibiting a golden sheen effect.
Snowflake Obsidian - A variety of obsidian containing white "snowflake" crystal patterns of the mineral cristobalite.
Photos of natural/un-cut material from mindat.org
Obsidian Simulants
Many. colored glasses are sold as "obsidian" especially, often flawless and brightly colored. These are obvious inexpensive fakes.
Physical Properties of Obsidian
Mohs Hardness5 to 5.5
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
More from other references
Specific Gravity2.35 to 2.60
Walter Schumann, Gemstones of the world (2001)
More from other references
Cleavage QualityNone
Walter Schumann, Gemstones of the world (2001)
FractureConchoidal
Walter Schumann, Gemstones of the world (2001) Large conchoidal, sharp edgedMore from other references
Optical Properties of Obsidian
Refractive Index1.450 to 1.550
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
More from other references
Optical CharacterIsotropic
Arthur Thomas, Gemstones (2009)
BirefringenceNone
Walter Schumann, Gemstones of the world (2001)
PleochroismAbsent
Walter Schumann, Gemstones of the world (2001)
Dispersion0.010
Walter Schumann, Gemstones of the world (2001)
Colour
Colour (General)Black, brown, partly iridescent or with silvery or golden sheen (opaque)
Brown, green, red (transparent)
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
More from other references
TransparencyTransparent,Translucent,Opaque
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
More from other references
LustreVitreous
Arthur Thomas, Gemstones (2009)
Fluorescence & other light emissions
Fluorescence (General)None
Walter Schumann, Gemstones of the world (2001)
Crystallography of Obsidian
Crystal SystemAmorphous
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
More from other references
HabitMassive
Arthur Thomas, Gemstones (2009)
Geological Environment
Where found:Occurs when volcanic lava is subjected to rapid heat loss.
Arthur Thomas, Gemstones (2009)
Inclusions in Obsidian
Torpedo shaped gas bubbles, needle-like inclusions, smooth undulating growth structure - Blue Chart Gem Identification, Herve Nicolas Lazzarelli, 2010, p 8

Gas bubbles, swirl marks, crystal inclusions, white spherolites ("snow flake obsidian") - Gemmological Tables, Ulrich Henn and Claudio C. Milisenda, 2004, p 2
Further Information
Mineral information:Obsidian information at mindat.org
Significant Gem Localities
Peru
 
  • Puno Department
    • Carabaya Province
[var: Macusanite]
USA
 
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