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We know three main classes of rocks, sedimentary, igneous, and metamorphic. In Limestone article, we learned how sedimentation occurs, and the formation of sedimentary rocks takes place. Today, we are going to know Obsidian rock, which falls in the main class igneous rocks.

We know igneous rocks have two basic types:

1. Intrusive Igneous Rocks

When molten lava/magma is cooling slowly below the surface of the earth and forms large crystals in the rocks they known as intrusive igneous rocks. For examples-

Diorite
Diorite
Gabbro
Gabbro
Granite
Granite
Pegmatite
Pegmatite

 

2 – Extrusive Igneous Rocks

When molten magma is cooling rapidly onto the surface of the earth and forms small crystals in the rocks they known as extrusive igneous rocks. For examples-

Obsidian
Obsidian
Andesite
Andesite
Basalt
Basalt
Dacite
Dacite
Pumice
Pumice
Rhyolite
Rhyolite
Scoria
Scoria
Fire Opal
Fire Opal

 

What Is Obsidian Rock?

If you strive to know the obsidian meaning, go ahead in this section. Obsidian is a class of igneous rocks, which forms when felsic lava extruded from a volcano onto the surface of the earth.

The cooling of lava takes place so rapidly that no chance remains for proper crystallization (Atomic Arrangements) and finds as an amorphous glass material. It has a smooth and uniform texture, which breaks with a conchoidal fracture.

Geological Classification of Obsidian Rocks:

Let’s see the classification of obsidian rocks at the perspectives of a geologist.

Class: Igneous Rocks

 

Sub-Class: Medium Hardness Rocks

Family-Group: Volcanic

Category: Opaque Rocks

Alternate Names: Lava, Glassy Lava, Xaga, Royal Agate, Glass Agate, Volcanic Glass, Glass Gem, Guardian Gem, and Black Beauty

 

Formation of Obsidian Rocks in Nature

We have seen in the earlier section that obsidian is an extrusive rock type and formation used to takes place on the surface of the earth when magma or lava coming out due to volcanic phenomena and rapid cooling takes place. The obsidian formation can happen in a variety of cooling environment such as

  • Along the edges of a flow of magma or lava
  • Along the edges of a dome of the volcano
  • Along the edges of a sill or dike, which takes place under the surface and it is the only intrusive type
  • The point where magma comes into the contact of water on the surface
  • The point where magma cools due to airborne cooling effects

 

Properties of Obsidian

Obsidians have various physical & visual properties, such as Hardness, Grain Size, Fracture, Streak (Colors), Porosity, Luster, and Strength. These all property attributes determine the applications of obsidian rocks. Let’s see some significant properties of obsidians.

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