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| Description: Form as magma cools and crystallizes Rocks formed inside Earth are called plutonic or intrusive rocks Rocks formed on the surface Formed from lava (a material similar to magma, but without gas Called volcanic or extrusive rocks Crystallization of magma Ions are arranged into orderly patterns Crystal size is determined by the rate of cooling Slow rate forms large crystals Fast rate forms microscopic crystals Very fast rate forms glass Classification is based on the rock’s texture and mineral constituents Texture Size and arrangement of crystals Types of igneous textures Fine-grained – fast rate of cooling Coarse-grained – slow rate of cooling Porphyritic (two crystal sizes) – two rates of cooling Glassy – very fast rate of cooling Vesicular – contains hole left by gas bubbles Pyroclastic – fragmented; produced by consolidation of volcanic fragments Picture Stats: Views: 267 Filesize: 270.26kB Height: 921 Width: 977 Source: https://biology-forums.com/index.php?action=gallery;sa=view;id=39374 |