A super-chilled igneous rock, black in colour and glassy in appearance. Fractures conchoidally. Often formed due to contact with cold seawater as the silicate minerals cool almost immediately, restricting mineral growth. Can also be called volcanic glass. Due to the rapid rate of cooling no crystals form. Obsidian forms from felsic, silica-rich, magma. Over time, crystals do form in a snowflake-like pattern, so-called “snowflake obsidian.
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GeologyRocks