Obsidian Value, Price, and Jewelry Information

OBSIDIAN: Mexico (banded and sheen varieties): Utah (“snowflake obsidian,” cabochon 30 x 40 mm). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Obsidian

Obsidian Information

Data Value
Name Obsidian
Is a Variety of Natural Glass
Varieties Apache Tears, Fire Obsidian, Mahogany Obsidian, Rainbow Obsidian, Sheen Obsidian, Snowflake Obsidian
Colors Black; gray, banded with brown streaks. Iridescence noted: gold, silver, blue, violet, green, and combinations of these colors, due to inclusions of minute bubbles that reflect light.
Crystallography Amorphous; usually as rounded masses ejected in volcanic eruptions, as small broken pieces, fine, hairlike filaments (for example, Pele’s Hair), and as flows.
Refractive Index 1.48-1.51; usually 1.49
Luster Vitreous.
Polish Luster Vitreous.
Hardness 5; 6 for basalt glass.
Wearability Poor
Fracture Conchoidal (best example of this type of fracture).Basalt glass may be splintery
Specific Gravity 2.25-3.00. (Typically 2.33-2.42; 2.70-3.00 for basalt glass).
Birefringence None, but crystals included in obsidian may be birefringent.
Cleavage None
Luminescence None.
Luminescence Present No
Transparency Transparent to opaque.
Phenomena Iridescence, chatoyancy.
Formula

Variable composition: SiO2 approximately 66-72% + oxides of Ca, Na, K, and so forth. Basaltic glass is ~5O% SiO2.

Pleochroism

None.

Optics

Isotropic.

Etymology

After Obsius, an explorer who discovered this material in Ethiopia, according to the Ancient Roman naturalist Pliny the Elder.

Occurrence

Obsidian is found in areas of present and former volcanic activity.

Inclusions

Elongated, torpedo-shaped bubbles, round bubbles, teardrop-shaped bubbles. Bubbles are often in parallel arrangement. Needlelike inclusions may give a silvery sheen. Protogenic silica minerals crystallizing in obsidian may be white and resemble snowflakes, hence the term snowflake obsidian.

“Obsidian,” showing conchoidal fractures, by Kevin Walsh is licensed under CC By 2.0

“Obsidian,” showing conchoidal fractures, by Kevin Walsh is licensed under CC By 2.0

Comments

Obsidian is naturally occurring volcanic glass.  This material is considered a rock. It’s heat sensitive and brittle, so cutting requires great care. Faceted gems tend to be very dark, except in small sizes. These pieces make delicate jewelry.

Varieties

This attractive material has a wide variety of appearances.

Snowflake obsidian, with spherulites of cristobalite, is widely used in jewelry as beads and cabochons.

Apache tears, which are cores of unaltered glass in nodular shells of decomposed obsidian, are popular among beginning hobbyists. Some of these have been faceted.

Mahogany obsidian has a reddish-brown color due to iron impurities.

Rainbow and fire obsidian show multiple brilliant colors due to inclusions of magnetite nanocrystals. Fire obsidian contains thinner layers of magnetite than the rainbow variety.

Sheen obsidian has a sheen produced by inclusions of gas bubbles.

Obsidian has been knapped into arrowheads and other tools since prehistoric times. This material can be shaped into a blade with a cutting edge sharper than surgical steel. “(HMM) Ancient technology - a broken piece of obsidian stone tool” by aotoro is licensed under CC By 2.0

Obsidian has been knapped into arrowheads and other tools since prehistoric times. This material can be shaped into a blade with a cutting edge sharper than surgical steel. “(HMM) Ancient technology – a broken piece of obsidian stone tool” by aotoro is licensed under CC By 2.0

Pele’s Hair is a light, string-like volcanic basalt glass that can become airborne.

Pele's hair can be found caught in trees and outdoor structures. “Pele's hair (DSC_3905)” by Thomas Tunsch is licensed under CC By-SA 2.0

Pele’s hair can be found caught in trees and outdoor structures. “Pele’s hair (DSC_3905)” by Thomas Tunsch is licensed under CC By-SA 2.0

Synthetics

Artificial or manufactured glass in blue, green, or red is sometimes passed off as obsidian. Natural obsidian does not form in these colors.  (However, these colors can be shown through iridescence). See the glass gem listing for more information.

Sources

The United States is a major source of gem-quality material.

  • Oregon: fire, mahogany, and rainbow varieties are known.
  • Wyoming: notably at Yellowstone National Park.
  • New Mexico: Apache tears.
  • Arizona; Colorado; California; Nevada: several localities.
  • Utah: major source of snowflake variety.
  • Hawaii: Pele’s hair and other varieties
  • Mexico: abundant, especially banded and sheen varieties.
  • Ecuador; Iceland; Indonesia; Italy; Japan.

Stone Sizes

Fragments range from microscopic to many inches across. Carvings up to 8-10 inches could be made. Larger pieces are available in place in certain localities.