Obsidian facts for kids
Quick facts for kids Obsidian |
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| General | |
| Category | Volcanic glass |
| Identification | |
| Color | usually black; sometimes green or brown; rarely yellow, orange, red or blue |
| Fracture | Conchoidal |
| Mohs scale hardness | 5–6 |
| Luster | Vitreous |
| Specific gravity | c. 2.4 |
| Optical properties | Translucent |
| Other characteristics | Texture: Smooth; glassy |
Obsidian is a type of natural volcanic glass. It forms when hot lava from a volcano cools down super fast. Because it cools so quickly, there isn't enough time for crystals to grow. This makes obsidian a smooth, glassy rock. It's a type of igneous rock, which means it comes from cooled magma or lava.
Obsidian comes from a special kind of lava called "felsic" lava. This lava is rich in light elements like silicon and oxygen. You often find obsidian where this type of lava has flowed out of a volcano. This lava is very thick, like super-thick syrup. Its thickness, combined with fast cooling, stops atoms from forming into crystals. That's how this natural glass is made!
Obsidian is a very hard and brittle rock. It breaks with super sharp edges, like broken glass. Because of its sharp edges, people in the past used it to make cutting tools and weapons. Today, some surgeons even use it for special scalpel blades!
Contents
What is Obsidian and How Does it Form?
The Roman writer Pliny the Elder wrote about a volcanic glass called obsidian. He said it was found in Ethiopia by a Roman explorer named Obsidius. That's where the name "obsidian" likely comes from!
Obsidian forms when lava cools very quickly. This can happen when lava flows out of a volcano and touches cool air or water. It can also form at the edges of a lava flow or inside cracks in the Earth where lava cools fast.
Obsidian is not considered a true mineral. This is because minerals have a specific crystal structure, and obsidian is a glass with no crystals. It's often called a mineraloid instead. Even though obsidian is usually dark, it's made of the same stuff as light-colored rocks like granite. It's mostly made of silicon dioxide (SiO2), which is like super-fine sand.
Obsidian doesn't last forever on Earth's surface. Over long periods, it slowly turns into tiny mineral crystals. This process is sped up by water. That's why you rarely find obsidian that's millions of years old.
Colors and Patterns of Obsidian
Pure obsidian is usually very dark, often black. But its color can change depending on tiny bits of other elements inside it. For example, iron can make it dark brown or black. Some rare obsidian is almost clear!
Sometimes, you can find white spots in black obsidian. These spots are tiny crystals called cristobalite. This type of obsidian is called snowflake obsidian.
Obsidian can also have cool patterns from gas bubbles trapped inside. These bubbles can make the obsidian look shiny or golden, which is called sheen obsidian. If you see a rainbow-like shimmer, it's called fire obsidian or rainbow obsidian. This happens because of tiny layers or particles that reflect light like a rainbow.
Where Can You Find Obsidian?
Obsidian is found near volcanoes that have had a certain type of eruption. You can find it in many places around the world, including Argentina, Japan, Mexico, New Zealand, Turkey, and the United States.
In the U.S., you can find large obsidian flows in places like Newberry Volcano and Medicine Lake Volcano in California. Yellowstone National Park also has a mountain of obsidian! Other western states like Arizona, Colorado, and Oregon also have deposits.
In the Mediterranean Sea, important obsidian sources are on islands like Lipari and Sardinia. In ancient times, islands like Milos and Gyali in Greece were major sources.
Obsidian's Past Uses
People have used obsidian for a very long time. The oldest evidence of its use dates back about 700,000 years ago in Kenya! In the Stone Age, obsidian was very valuable. Just like flint, it could be shaped into incredibly sharp blades and arrowheads. This shaping process is called knapping.
Obsidian breaks in a special way called a "conchoidal fracture." This means it breaks with smooth, curved surfaces, like the inside of a seashell. This type of break creates those super sharp edges. Ancient people also polished obsidian to make early mirrors.
Scientists today can even figure out how old an obsidian artifact is by studying how much water it has absorbed over time. This is called obsidian hydration dating.
Obsidian in Europe
Obsidian tools first appeared in Europe a long time ago. They became very common during the Upper Paleolithic period. Obsidian was important for sharing new ideas and skills during the Neolithic revolution. People used it to make sharp tools.
Obsidian from the Greek island of Milos was traded far and wide. People in Hungary and Slovakia got their obsidian from local sources. These tools traveled thousands of kilometers, showing how valuable obsidian was! A famous obsidian mirror, brought from Mexico, was owned by John Dee in Europe in the 1500s.
Obsidian in the Middle East and Asia
In ancient Turkey, people made blades from obsidian around 5,000 BC. The Ancient Egyptians imported obsidian from areas near the Red Sea. They used it for tools, mirrors, and decorations.
In Japan, people living near volcanoes also used obsidian tools. They mined it during the Jōmon period.
Obsidian tools have even been found in Israel. Scientists studied these tools and found that the obsidian came from Turkey. This helped them learn about ancient trade routes!
Obsidian in the Americas
Ancient people in Mesoamerica (like the Maya and Aztec) used obsidian a lot. They were very skilled at carving it into tools and beautiful objects. They even made a type of sword called a macuahuitl. This weapon had sharp obsidian blades set into a wooden body. It could cause terrible injuries!
Obsidian mirrors were special to some Aztec priests. They believed these mirrors could help them see visions and predict the future. These mirrors were linked to Tezcatlipoca, the god of obsidian and magic. His name means 'Smoking Mirror'.
Native American people traded obsidian all across the Americas. Each volcano produces a slightly different type of obsidian. This allows archaeologists to trace where an obsidian tool came from. For example, obsidian found in Greece has been traced back to specific islands like Milos.
Obsidian in Oceania
The Lapita culture, which lived across the Pacific Ocean around 1000 BC, used many obsidian tools. They traded obsidian over long distances. The way they made and stored these tools suggests that obsidian was not just practical, but also a sign of importance or high status.
On Rapa Nui (Easter Island), people used obsidian for tools like Mataia. They also used it for the pupils of the eyes of their huge Moai statues, which were surrounded by bird bone rings. Obsidian was even used to carve the mysterious Rongorongo writing.
Modern Uses of Obsidian
Obsidian can still be used to make extremely sharp knives. Some surgeons use obsidian blades for very delicate operations. These blades can be much sharper than steel scalpels. When you look at a steel blade under a powerful microscope, it looks jagged. But an obsidian blade looks smooth, even under an electron microscope!
The main problem with obsidian blades is that they are brittle. They can break more easily than metal blades. So, they are used for special surgeries where this isn't a big concern.
Obsidian is also used for decoration and as a gemstone. It can look different depending on how it's cut. From one angle, it might look jet black, but from another, it might be a shiny gray. Small, rounded pieces of obsidian are sometimes called "Apache tears".
Since the 1970s, some high-quality audio turntables have used obsidian for their bases.
Images for kids
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A piece of obsidian.
See also
In Spanish: Obsidiana para niños
- Apache tears
- Helenite
- Hyaloclastite and tachylite – volcanic glasses
- Knapping
- Libyan desert glass
- Mayor Island / Tūhua - a source of Māori obsidian tools
- Obsidian hydration dating
- Stone tool
- Yaxchilan Lintel 24 – Ancient carving showing a Maya bloodlet ritual involving a rope with obsidian shards.
