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How is Lava Glass Made?

Published in Volcanic Glass Formation 2 mins read

Lava glass, also known as volcanic glass, is made by the rapid chilling of liquid lava when it cools too quickly for crystals to form.

The Science Behind Volcanic Glass

The formation of lava glass is a direct result of molten rock, or lava, experiencing a very fast cooling process. When liquid lava erupts onto the surface or interacts with its surroundings, its high temperature drops dramatically if it comes into contact with cooler elements.

According to the reference, volcanic glass is formed by rapid chilling of liquid lava when it comes into contact with the atmosphere, water, or cooler adjacent rocks. Unlike slow cooling that allows minerals to crystallize, this rapid chilling freezes the atomic structure of the lava before crystals have time to grow, resulting in a glassy, non-crystalline solid.

Different Forms of Lava Glass

This rapid cooling process creates various types of volcanic glass, depending on the composition of the lava and the specific cooling conditions.

Type of Lava Glass Description/Occurrence Mentioned
Obsidian Found mainly in lava flows, domes, and dykes
Pitchstone Found mainly in lava flows, domes, and dykes
Perlite Found mainly in lava flows, domes, and dykes
Pumice Found in pyroclastic rocks
Cinder Found in pyroclastic rocks
Ash Found in pyroclastic rocks

Obsidian is perhaps the most well-known form, recognized for its smooth, dark, and often shiny appearance. Pumice, on the other hand, is a vesicular (bubbly) form of volcanic glass created when gas-rich lava cools rapidly, trapping bubbles within the glass structure.

Key Factor: Rapid Cooling

The defining characteristic for the creation of all these forms of volcanic glass is the speed at which the liquid lava cools. It's this lack of time for crystal formation that differentiates volcanic glass from crystalline igneous rocks like granite or basalt.