Obsidian is one of the most fascinating minerals. However, it's not technically a rock—it's natural volcanic glass.
While typically black, obsidian can exhibit a variety of colors based on the minerals it contains. Some common varieties include mahogany, snowflake, rainbow, and gold or silver sheen obsidian.
When obsidian breaks, it doesn't fracture along straight lines or smooth planes. Instead, it forms curved, shell-like patterns known as conchoidal fractures—named for their resemblance to the inside of a seashell.
On the Mohs hardness scale, obsidian ranks between 5 and 6, making it slightly more rigid than ordinary glass.
This shiny, glass-like material has been prized for its striking appearance, razor-sharp edge, and ease of shaping. This unique rock has been used for tools, jewelry, and art throughout history, making it scientifically and culturally significant.
Let's explore how it forms, how to identify it, its value, and the best places to find it.
Obsidian Formation
Obsidian is made primarily of silica, the same material found in quartz and glass, which explains its smooth, shiny appearance. It forms when hot lava cools so rapidly that atoms don’t have time to arrange into crystals. This absence of crystal structure gives obsidian its distinctive glassy look and sharp edges.
This process typically occurs during volcanic eruptions when molten rock, or magma, reaches the surface and flows as lava. Once exposed to air or water, the lava cools almost instantly, creating obsidian’s smooth, glassy texture.
Imagine melting sugar and pouring it onto a cold surface—it hardens quickly before forming grains. Lava behaves similarly when it cools rapidly, producing volcanic glass.
Obsidian often forms near the edges of a lava flow or on the surface of volcanic domes. These areas cool faster than the center of the lava flow due to exposure to cooler air and surrounding terrain. Volcanic domes—large mounds of thick, slow-moving lava—frequently have obsidian along their edges, where the rapid cooling creates natural glass.
Another common source of obsidian is where lava flows into water. The sudden drop in temperature from the water accelerates the cooling process even more, forming glass-like obsidian almost instantly.
Guide to Obsidian Identification
Examine the Appearance
Obsidian is easily recognized by its smooth, glass-like surface and distinctive shine. Once you know what to look for, it's hard to mistake it for any other material.
While pure obsidian is typically dark, its color can vary based on the minerals it contains.
Obsidian Colors
Black obsidian: This is the most common type. Its dark color comes from the high iron and magnesium content in the lava.
Rainbow obsidian: Displays iridescent layers due to microscopic inclusions of magnetite or hematite.
Snowflake obsidian: Features white or gray spots (spherulites) caused by cristobalite crystals forming during cooling.
Mahogany obsidian: A reddish-brown variety, its hue is due to the presence of iron oxide.
Green or blue obsidian: Less common; these colors can result from iron or other specific mineral inclusions.
Gold or silver sheen obsidian: The shimmering effect is caused by gas bubbles trapped during the lava's rapid cooling.
Feel the Texture
You'll notice how smooth it feels when you hold obsidian. Run your fingers across the surface – it's almost slippery. While it feels smooth, obsidian is incredibly sharp. Be careful when handling it, especially along its edges.
Look for Special Visual Effects
Obsidian often contains tiny gas bubbles trapped during its formation, which can create beautiful visual effects.
When these bubbles are arranged in flat layers, they can produce a gold or silver sheen, known as sheen obsidian. It's one of my favorite types because the light catches it in such a beautiful way.
Check for a Conchoidal Fracture
If you’re unsure whether you have found obsidian, examine any broken edges. A smooth, curved surface—known as a conchoidal fracture—is a key indicator. This kind of break is typical of obsidian and other glassy materials.
When I find an obsidian piece, I always check the edges. The fracture lines can be a clear giveaway. Plus, they look really cool.
Use Light to Check Transparency
Obsidian might look completely black, but it's often slightly translucent. Hold a thin piece up to the light, such as sunlight or a flashlight. If you notice light passing through, especially around the edges, it's likely obsidian. This technique works best with thinner pieces.
Summary of Identification Tips
To quickly identify obsidian, follow these steps:
- Look for a smooth, glassy texture
- Observe color variations caused
- Feel for sharp edges resulting from conchoidal fractures
- Hold it up to the light to check for slight translucency
- Watch for special effects like gold or silver sheen from trapped gas bubbles.
Notable Obsidian Deposits
Obsidian can be found in volcanic regions around the globe. Some notable locations with rich obsidian deposits include:
United States
Oregon
Glass Butte is the largest obsidian deposit in the world, known for its rainbow, gold, and silver-sheen obsidian.
The Newberry Big Obsidian Flow is a prominent site for obsidian, formed during a relatively recent volcanic eruption around 1,300 years ago.
Wyoming
The Obsidian Cliff in Yellowstone National Park is a historic site with high-quality obsidian used by Native Americans for tools and trade.
Other Countries
Mexico
The region surrounding the Trans-Mexican Volcanic Belt is home to significant obsidian sources, especially in areas like Pachuca.
Italy
The Lipari Islands off the coast of Sicily have been a source of obsidian for thousands of years. In ancient times, obsidian from Lipari was traded all over the Mediterranean.
Turkey
The Anatolian region, particularly near the town of Kütahya, has been a source of obsidian since ancient times.
Obsidian Lapidary Use
Working with obsidian can be challenging due to its brittle nature, but with the right approach, you can create beautiful and sharp pieces. Here are a few tips based on my experience:
- Use a soft polishing medium: Since obsidian is prone to chipping, avoid using harsh abrasives during the polishing process.
- Wear protective gear: Obsidian shards are razor-sharp and can easily fly off while working. Always wear gloves and protective glasses to prevent injury.
- Flintknapping: Obsidian is perfect for flintknapping because it breaks easily into sharp edges, making it ideal for crafting arrowheads, knives, and other cutting tools.
Apache Tears – Pebbles of Obsidian
Apache tears are one the most prized types of obsidian. These small, rounded pebbles of volcanic glass carry a rich legend. According to Apache lore, they represent the tears of the women who mourned the loss of their warriors in battle.
Apache tears are primarily found in Arizona, Colorado, Nevada, New Mexico, Oregon, and Utah.
History of Obsidian Use
For centuries, ancient cultures used obsidian for cutting tools, weapons, and even Obsidian mirrors. The Aztecs used obsidian for ceremonial knives and mirrors, while Native Americans used it for arrowheads.
Even today, obsidian is used in modern surgical tools due to its ability to produce incredibly fine edges.
Obsidian was highly valuable in ancient trade. Archaeologists can trace ancient trade routes by studying where obsidian artifacts were found, often tracing them back to specific volcanic regions.
Obsidian Lore
In Aztec and Mayan cultures, obsidian held deep spiritual significance and was connected to their gods and rituals.
- Itzpapalotl, the "obsidian butterfly goddess," represented beauty and fierce protection. Her wings, made of obsidian blades, symbolized the dual forces of life and death.
- Itztlacoliuhqui, the "god of the curved obsidian blade," represented punishment and the consequences of wrongdoings, embodying the sharp, unforgiving nature of obsidian itself.
