NATS 1750 Lecture Notes - Lecture 6: Volcanic Glass, Oceanic Crust, Particle Size
13 Apr 2016
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Document Summary
Rocks are mainly mixtures of minerals, though there are some things like coal or volcanic glass that are exceptions to this. There are 3 main types - these arise from how the rock is formed. Igneous rock forms from molten rock magma. If molten rock reaches the surface it is called lava. When it solidifies at surface lava becomes extrusive or volcanic rock. (however, if magma solidifies underground (and a lot of it does) it is called intrusive or plutonic) Very important to the properties of the resultant rock is the cooling rate (temperature again!) Rate of cooling produces texture - very rapid cooling -glassy or frothy texture. As rate of cooling slows, grains in rock tend to become larger. Igneous rock is mainly silicates, but the exact mixtures varies. ~ dark silicates includes olivine, pyroxene, amphibole etc are richer iron or magnesium. ~ light silicates higher silica content quartz & feldspars.
