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Notes for Exam 1

Notes for Exam 1 - 8.29.07 9.5.07 Rock cycle Rocks are...

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8.29.07, 9.5.07 Ÿ Rock cycle Ÿ Rocks are sources of natural resources Ÿ They can tell us about past history Ÿ Basic knowledge is req to understand earth phenomena Ÿ Ÿ 3 Types of Rocks Ÿ Igneous Ÿ Made of cooled magma, or melted rock UNDER the surface (crystallization). Hot, thick fluid of liquids, gases, and solids. Ÿ Solids - mineral crystals, as ions (charged particles) moving freely within the melt Ÿ Crystallization - Magma cools, the movement of ions slow and are arranged into orderly patterns Ÿ Crystal size depends on rate of cooling of the magma or lava Ÿ Slow cooling = large crystals Ÿ Fast cooling = microscopic cooling Ÿ VERY fast rate = glass (amorphous solid) Ÿ Magma is buoyant Ÿ Magma made of silicate minerals (most abundant mineral grp on planet). Some water vapor in them but not a lot. Ÿ If the magma reaches the surface it is lava (melted rock AT the surface). Ÿ Eruptions may be explosive or fluid Ÿ Igneous rocks formed at the surface Ÿ Extrusive Ÿ Volcanic Ÿ Classification is based on the texture and mineral constituents Ÿ Texture - overall appearance Ÿ Size and arrangment of crystals Ÿ Indicative of environment of formation Ÿ Fine grained - fast rate of cooling Ÿ Coarse grained - slow rate of cooling Ÿ Prophetic (two crystal sizes) - two rates of cooling Ÿ Glassy - very fast reate of cooling Ÿ Vesicular - vesicles aor bubbles” formed by gas escaping from the melt during rapid cooling Ÿ Rhyolite has a fine grained texture Ÿ Granite - coarse grained Ÿ Dark silicates = rich in iron and/or magnesium Ÿ Basaltic rocks Ÿ Light silicates = greater amt of potassium, sodium, and calcium Ÿ Granitic - felsic Ÿ Andesitic - intermediate Ÿ Andesite Ÿ Ultramafic Ÿ Bowen’s Reaction series Ÿ Magma crystallizes over a temp range of several hundred degrees Ÿ Crystallize in a predictable order Ÿ Last ones formed are very diff from first Ÿ Sedimentary Ÿ Metamorphic Ÿ Igneous rocks
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Ÿ Formed at the depth, beneath the surface. Ÿ Intrusive (batholith) - Stome Mtn, Yosemite Nat’l Park Ÿ Plutonic Ÿ Cooling and crystallization Ÿ Textures and weather compositions Ÿ Weathering - a natural response of Earth’s materials to a new environment. A gradual change to a state of equilibrium. Ÿ Mechanical Weathering - the PHYSICAL breaking apart of Eart’s material Ÿ Result: rock is broken down into smaller pieces generally retaining properties of the original rock. Ÿ Frost wedging: splitting of rocks due to alternate freezing and thawing of water in cracks or voids (potholes) Ÿ Water expands ~9% when it freezes Ÿ Increase in volume exerts a tremendous outward force, enlarging any opening Ÿ Unloading - slabs of rock that “peel” away due to a reduction in pressure when overlaying rock is eroded away - sheeting Ÿ Biological activity - activities of plants and burrowing animals Ÿ Chemical weathering - alters the internal structure of the minerals by removing and/or adding elements Ÿ Water - most impt agent Ÿ Reactions such as oxidation of dissolution by acids serve to decompose rocks.
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