search
  • Sign In
    Sign Up
  • English speaking customer support only

    1-800-464-1640

  • Change Language
  • USD
By Gavin Clarke Reviewed By Andreas Zabczyk Oct 13, 2009 Updated Aug 23, 2017

Obsidian: Volcanic Glass

When you buy a gem, you want to be sure that it is a natural stone and not glass. But there is one kind of natural gemstone that actually is glass. Obsidian is naturally occurring volcanic glass. It is formed when felsic lava extruded from a volcano cools without crystal growth. Obsidian has been known since prehistoric times, and has some fascinating properties as well as some important practical uses.

Obsidian Rough Stone
Obsidian Rough Stone

Obsidian is mineral-like, but is not a true mineral because it is not crystalline and does not have a well-defined chemical composition. Usually obsidian is at least 70% silicon dioxide. Pure obsidian is usually dark in color, though the color varies depending on the presence of impurities. Iron and magnesium give the obsidian a dark-green, brown or black color.

Gold-Sheen Obsidian
Gold-Sheen Obsidian

In some stones, small white inclusions of radially clustered cristobalite crystals in the black glass produce a blotchy or snowflake pattern, and this is known in the gem trade as snowflake obsidian. Obsidian may contain patterns of gas bubbles remaining from the lava flow, aligned along layers created as the molten rock was flowing before being cooled. These bubbles can produce interesting effects such as a golden or rainbow sheen.

Since obsidian is composed mainly of silicon dioxide, it has similarities to quartz. However, since obsidian is not crystalline, it is not as hard as quartz. Obsidian has a hardness of 5 to 5.5 on the Mohs scale. It also has a lower density (2.35 to 2.60) and refractive index than quartz (1.45 to 1.55). Unlike quartz, obsidian is singly refractive.

Snowflake Obsidian
Snowflake Obsidian

In addition to its use as a gemstone, obsidian has been used in cardiac surgery, since well-crafted obsidian blades have a cutting edge many times sharper than high-quality steel surgical scalpels, with the edge of the blade being only about 3 nanometers wide. Even the sharpest metal knife has a jagged, irregular blade when viewed under magnification. When examined under an electron microscope an obsidian blade is still smooth and even.

Obsidian is found in many locations that have seen volcanic activity, including Ecuador, Japan, Italy, Iceland, Indonesia, Mexico and the USA.

STAY IN TOUCH
*You're signing up to receive GemSelect promotional email.
Partners and Trust Payment options

Switch to Mobile Version

Privacy Notice © 2005-2023 GemSelect.com all rights reserved.

Reproduction (text or graphics) without the express written consent of GemSelect.com (SETT Company Ltd.) is strictly prohibited.

1078

More Shapes
Popular Gemstones
  • Sapphire
  • Emerald
  • Ruby
  • Aquamarine
  • Zircon
  • Opal
  • Topaz
  • Tourmaline
  • Garnet
  • Amethyst
  • Citrine
  • Tanzanite
All Gemstones (146)
A B C D E F G H I J K L M N O P Q R S T V Z
  • Actinolite Cat's Eye
  • Agate
  • Agate Geode
  • Almandine Garnet
  • Amazonite
  • Amethyst
  • Amethyst Geode Slice
  • Ametrine
  • Ammolite
  • Andalusite
  • Andesine Labradorite
  • Apatite
  • Aquamarine
  • Aventurine
  • Azotic Topaz
  • Azurite
  • Black Opal
  • Bloodstone
  • Boulder Opal
  • Carnelian
  • Cat's Eye Apatite
  • Cat's Eye Aquamarine
  • Cat's Eye Gemstones
  • Cat's Eye Moonstone
  • Cat's Eye Opal
  • Cat's Eye Scapolite
  • Chalcedony
  • Charoite
  • Chocolate Opal
  • Chrome Diopside
  • Chrysoberyl
  • Chrysoberyl Cat's Eye
  • Chrysocolla
  • Chrysoprase
  • Citrine
  • Color Change Gemstones
  • Color-Change Diaspore
  • Color-Change Fluorite
  • Color-Change Garnet
  • Coral
  • Demantoid Garnet
  • Dendritic Agate
  • Diamond
  • Druzy Amethyst
  • Druzy Azurite
  • Druzy Citrine
  • Druzy Variscite
  • Emerald
  • Enstatite
  • Fire Agate
  • Fire Opal
  • Fluorite
  • Fossil Coral
  • Garnet
  • Golden Beryl
  • Grandidierite
  • Grossularite Garnet
  • Hawk's Eye
  • Hematite
  • Hemimorphite
  • Hemimorphite Druzy
  • Hessonite Garnet
  • Howlite
  • Idocrase
  • Imperial Topaz
  • Iolite
  • Jade Gemstones
  • Jadeite
  • Jasper
  • Kornerupine
  • Kunzite
  • Kyanite
  • Labradorite
  • Lapis Lazuli
  • Larimar
  • Malachite
  • Malaya Garnet
  • Mali Garnet
  • Maw-Sit-Sit
  • Moonstone
  • Morganite
  • Mother Of Pearl
  • Mystic Quartz
  • Mystic Topaz
  • Nuummite
  • Obsidian
  • Onyx
  • Opal
  • Opal Doublet
  • Opal In Matrix
  • Pearl
  • Peridot
  • Pietersite
  • Prehnite
  • Psilomelane Dendrite
  • Pyrite
  • Pyrope Garnet
  • Quartz
  • Quartz Cat's Eye
  • Quartz With Hedenbergite
  • Quartz With Marcasite
  • Rainbow Moonstone
  • Rainbow Pyrite
  • Rhodochrosite
  • Rhodolite Garnet
  • Rhodonite
  • Rose Quartz
  • Rubellite Tourmaline
  • Ruby
  • Ruby In Fuchsite
  • Ruby-Zoisite
  • Rutile Quartz
  • Sapphire
  • Scapolite
  • Scolecite
  • Seraphinite
  • Serpentine
  • Sillimanite
  • Sillimanite Cat's Eye
  • Smithsonite
  • Smoky Quartz
  • Snowflake Obsidian
  • Sodalite
  • Spectrolite
  • Spessartite Garnet
  • Sphalerite
  • Sphene
  • Spinel
  • Star Diopside
  • Star Garnet
  • Star Gemstones
  • Star Moonstone
  • Star Rose Quartz
  • Star Ruby
  • Star Sapphire
  • Strawberry Quartz
  • Sunstone
  • Tanzanite
  • Tiger's Eye
  • Tiger's Eye Matrix
  • Topaz
  • Tourmaline
  • Tsavorite Garnet
  • Turquoise
  • Variscite
  • Zircon
Main Categories
  • New Arrivals
  • Gemstone Lots
  • Calibrated Gemstones
  • Gemstones By Piece
  • Top Grade Gems
  • Matching Pairs
  • Cabochon Gemstones
  • Drilled Gems, Briolettes and Beads
  • Birthstones
  • Gemstone Carvings
  • Fancy Gemstones
  • Star Gemstones
  • Unheated Sapphire
English speaking customer support only

Toll Free - USA & Canada only:
1-800-464-1640

International:
+66-39609697

Save Money
No shipping Fees for Additional Items!
$8.90 Worldwide Shipping

Update Translation
 
Current Value
New Value
GemSelect Gemstones
X Close Window
Colored Gemstones
X Close Window
Colored Gemstones
X Close Window
Colored Gemstones
Size and Weight

Gems are always measured in Millimeter (mm)

Dimensions are given as;
length x width x depth,
except for round stones which are;
diameter x depth

Select gems by size, not by weight!
Gem varieties vary in density, so carat weight is not a good indication of size

Note: 1ct = 0.2g

Size Comparison Chart