![]() ![]() These two basic types of lava can produce what we call obsidian, but true obsidian forms from felsic lava cooled rapidly. ![]() You see this in the lava flows of Hawaii that flow rapidly spreading over the land often solidifying on the surface and continuing to flow underneath the new crust. Mafic lava is more fluid and, when hot enough, flows almost like a river. This inhibits atomic diffusion, the movement of molecules needed to form crystals. Lava that’s high in silica tends to be viscous, move slowly and develop thicker, solid flows. Rhyolite rock is a prime example of high silica lava. They are composed of quartz and feldspar so they are lighter hued. Basalt is a common form of mafic lava.įelsic lavas are just the opposite, high in silica and low in iron and magnesium minerals. Mafic lavas are dark, dense and made primarily of dark iron and magnesium minerals but are low in the lighter elements that make up the silica minerals and rocks. There are two major types of lava based on their mineral content and chemistry - mafic and felsic. Under other conditions, it can be vitreous, glassy and gemmy. Under the right conditions, we can find gem agate, fire agate or even mineral crystals. Depending on its gas content, the hardened lava can be vuggy meaning it contains pores or voids. Its layers are dense, seldom revealing any crystals. Normally when lava flows, it ends up as thick layers of solid rock. Is it a mineral? The answer lies in how it’s formed. Obsidian is a volcanic glass that’s formed when molten lava cools suddenly. ![]()
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