|Snowflake Obsidian. Photo: spiritrockshop|
Obsidian, a dark volcanic glass, has a smooth, glossy appearance. Snowflake obsidian is a type of black obsidian with white or grayish spots. These spots are called spherulites, and they are composed of needle-shaped cristobalite, a type of quartz.
Snowflake Obsidian is usually black in color, with white patches called Phenocryst. It resembles snowflakes, hence the name.
Snowflake Obsidian is formed when the felsic lava from a volcano rapidly cools down with very minimum crystal growth. It’s basically a volcanic glass that formed as an igneous rock.
Obsidian's high silica content makes the lava it forms from highly viscous, or thick. It also has a low water content, since as the magma reaches the surface, most of the water evaporates as steam. The lava therefore moves quite slowly. The composition of obsidian can change over time, just as any type of rock changes over time, moving through different phases of the rock cycle.
Obsidian is an easily recognizable igneous rock. It is a glassy-textured, extrusive igneous rock. Obsidian is a natural glass - it lacks crystals, and therefore lacks minerals. Obsidian is typically black in color, but most obsidians have a felsic chemistry. Felsic igneous rocks are generally light-colored, so a felsic obsidian seems a paradox. Mafic obsidians are scarce, but they have the same appearance.
Obsidian forms two ways:
1) very rapid cooling of lava, which prevents the formation of crystals.
2) cooling of high-viscosity lava, which prevents easy movement of atoms to form crystals. An example of obsidian that formed the first way is along the margins of basaltic lava flows at Kilaeua Volcano (Hawaii Hotspot, central Pacific Ocean).
It’s also known as White Snowflake Obsidian and Gray Snowflake Obsidian.Large deposits of Snowflake Obsidian can be found in Mexico, Iceland, and the USA.
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