What Is Obsidian? About The Igneous Rock
WHAT IS OBSIDIAN – In this topic, we are going to know about the igneous rock from volcanic glass known as obsidian.
It is a naturally occurring volcanic glass that is formed as an extrusive igneous rock. It is produced when felsic lava extruded from a volcano rapidly cools with minimal crystal growtn.
This rock can be found within the margins of rhyolitic lava flows known as obsidian flows. The flows are where the chemical composition causes a high viscosity, which results in a natural glass forming from the lave upon rapid cooling.
It is a mineral-like but not a true mineral since it is not crystalline as a glass and is usually regarded as a mineraloid. The rock consists mainly of SiO2 or silicon dioxide, which is usually 70% by weight or more.
Pure types are usually dark in appearance, but the color varies depending on the impurities present. What gives the rock its dark brown to black color are Iron and other transition elements. Most black types contain nanoinclusions of magnetite, an iron oxide. There are some samples that are nearly colorless.
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