Table of Contents
Where does obsidian form?
Origin and properties Obsidian is formed from quickly cooled lava, which is the parent material. Extrusive formation of obsidian may occur when felsic lava cools rapidly at the edges of a felsic lava flow or volcanic dome, or when lava cools during sudden contact with water or air.
How are obsidian formed?
obsidian, igneous rock occurring as a natural glass formed by the rapid cooling of viscous lava from volcanoes. Obsidian is extremely rich in silica (about 65 to 80 percent), is low in water, and has a chemical composition similar to rhyolite.
How is obsidian extracted from the Earth?
Because obsidian is easy to break (like glass), collecting samples from an outcrop is relatively simple. A good rock hammer will easily break large chunks of volcanic glass into small, usable pieces. However, make sure to bring a good collection bag because obsidian tends to be quite heavy.
Can crystals form above ground?
When magma cools within the Earth, the cooling proceeds slowly. Slow cooling allows time for large crystals to form, so intrusive igneous rocks have visible crystals. Extrusive igneous rocks form above the surface. The lava cools quickly as it pours out onto the surface (Figure below).
Where does green obsidian come from?
It is commonly found within the margins of rhyolitic lava flows known as obsidian flows, where the chemical composition (high silica content) gives rise to a high viscosity that forms a natural lava glass after rapid cooling.
What type of rock is obsidian and how it is formed?
Obsidian is an “extrusive” rock, which means it is made from magma that erupted out of a volcano. If it was an igneous rock that formed from magma underground and did not erupt, it would have been called an “intrusive” rock. Obsidian: Can we get started already? I don’t have all day!
Where was obsidian first found?
Mesopotamia
Since obsidian is the result of volcanic activity and lava eruptions, it is formed in nature where there are active volcanoes, dormant or extinct. Therefore, the scope of its distribution is quite wide. The mineral was first discovered 9,000 years ago in Mesopotamia.
Where is black obsidian found?
Obsidian can be found all over the world in areas with volcanic activity. For example, significant deposits of obsidian can be found in the United States, Canada, Mexico, Guatemala, Argentina, Chile, Greece, Hungary, Italy, Iceland, Russia, New Zealand, Japan, and Kenya.
Is formed from granite?
Granite is an igneous rock and is formed from magma. Granitic magma has many potential origins but it must intrude other rocks. Most granite intrusions are emplaced at depth within the crust, usually greater than 1.5 kilometres and up to 50 km depth within thick continental crust.
Where does yellow obsidian come from?
Natural Yellow Obsidian There may be instances where you happen upon a yellow-looking glass stone that really did solidify under the Earth, when volcanic lava was cooling. This is not natural yellow obsidian, but rather a mix between brown and orange obsidian that has, as a result, taken on a yellowish hue.
Is Blue obsidian man-made?
This is a man-made stone. Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock. It is produced when felsic lava extruded from a volcano cools rapidly without crystal growth.
Are there any igneous rocks similar to obsidian?
Granites and rhyolites can form from the same magma as obsidian and are often geographically associated with the obsidian. Rarely, volcanic glasses are found with a composition similar to basalt and gabbro. These glassy rocks are named “tachylyte.” Are There Other Glassy Igneous Rocks?
Where can obsidian be found in the world?
The Valles Caldera in New Mexico is a particularly good example, with a huge lava flow and several lava domes all constructed from obsidian.
How big is the average size of an obsidian rock?
Obsidian: The specimen shown above is about two inches (five centimeters) across. The curved semi-concentric ridges are breakage marks associated with obsidian’s conchoidal fracture. The rock has very sharp edges.
What causes obsidian to break into small pieces?
The conchoidal fracture of obsidian causes it to break into pieces with curved surfaces. This type of fracturing can produce rock fragments with very sharp edges. These sharp fragments may have prompted the first use of obsidian by people.