Thursday January 20, 2011 (Igneous Rocks)

The Launch Pad Thursday, 1/20/11 Which types of rocks can be weathered into sediment? Igneous, metamorphic, or even sedimentary rocks can all be weathered into sediment. Describe the process of lithification. Lithification occurs when sediment is deposited in layers, which are compacted by the weight of the layers above. The pressure on the sediment layers cement them into sedimentary rocks.

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Assignment Currently OpenDate IssuedDate Due WS – The Rock Cycle1/191/21

Igneous rocks form as magma cools and crystallizes. Rocks formed on the surface are formed from lava (a material similar to magma, but without gas) are called volcanic or extrusive rocks. Rocks that are formed inside the Earth are called plutonic or intrusive rocks.

When magma crystallizes, its ions are arranged into orderly patterns. The size of the crystal is determined by the rate of cooling. Slow cooling rates form large crystals. Fast cooling rates form microscopic crystals. Very fast cooling rates form glass.

Classification of igneous rocks is based on the rock’s texture and mineral constituents. Texture refers to the size and arrangement of the crystals in the rock. Types of igneous rock textures: Coarse-grained – slow rate of cooling Fine-grained – fast rate of cooling graniteandesite

Classification of igneous rocks is based on the rock’s texture and mineral constituents. Texture refers to the size and arrangement of the crystals in the rock. Types of igneous rock textures: Glassy – very fast rate of cooling Porphyritic (two crystal sizes) – two rates of cooling obsidianpumice porphyritic granite

Figure 3.5

Figure 3.5 A

Figure 3.5 B

Figure 3.5 D

Glassy (obsidian) Figure 3.7

Figure 3.8 pumice

Mineral composition is, of course, the types of minerals that make up the rock. The crystallization of magma is explained by Bowen’s Reaction Series, which shows the order of mineral crystallization. This is influenced by crystal-settling in the magma. Bowen’s Reaction Series is shown on the next slide.

Figure 3.13 Bowen’s reaction series

Magma, with its diverse chemistry, crystallizes over a temperature range of a t least 200 o C. Therefore, as magma cools, certain minerals crystallize first, at relatively high temperatures. At successively lower temperatures, other minerals crystallize. This arrangement of minerals became known as Bowen’s Reaction Series.

The first mineral to crystallize from a mass of magma is olivine. Further cooling results in the formation of pyroxene, as well as plagioclase feldspar. At intermediate temperatures, the minerals amphibole and biotite begin to crystallize.

During the last stage of crystallization, after most of the magma has solidified, the minerals muscovite and potassium feldspar may form. Finally, quartz crystallizes from any remaining temperature.

In nature, we find that minerals that form in the same general temperature range on Bowen’s chart are found together in the same igneous rocks. For example, the minerals quartz, potassium feldspar, and muscovite are typically found together as major components of the igneous rock granite.

Figure 3.13 Bowen’s reaction series

Worksheet Igneous Rocks (Part 1)