what is obsidian

Obsidian is a naturally occurring volcanic glass formed when lava extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock, produced from felsic lava rich in lighter elements such as silicon, oxygen, aluminum, sodium, and potassium. Obsidian is hard, brittle, and amorphous, and it fractures with sharp edges. It is usually dark in color, similar to mafic rocks such as basalt, but its composition is extremely felsic, consisting mainly of silicon dioxide. Obsidian can be found in various colors, including black, red, brown, and green, and it is known for its conchoidal fracture, which causes it to break into pieces with razor-thin and extremely sharp curved surfaces. Obsidian has been historically used to manufacture cutting and piercing tools, and it has been used experimentally as surgical scalpel blades. It is also used to make jewelry due to its smooth, glassy texture. Obsidian is found in areas with volcanic activity and is associated with volcanic rocks, forming the upper portion of rhyolitic lava flows. It has been used throughout history to make tools, weapons, and decorative objects, and some modern surgical scalpels are made from obsidian.