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6.1 Rocks and the Rock Cycle Three Major Types of Rock • rock~ collection of one or more minerals or organic material • Igneous~ forms when magma or lava hardens and cools • Magma~ molten rock beneath Earth’s surface • Lava~ molten rock above Earth’s surface • Sedimentary~ formed when sediment deposits ( rock, mineral crystals, and organic matter broken in fragments) harden • Metamorphic rock~ rock that forms when existing rock is altered (pressure and heat) The Rock Cycle • ~ series of processes in which rock forms, changes from one type to another, is destroyed, and forms again by geological processes Properties of Rocks • All rock has physical and chemical properties that are determined by how and where rock formed • Bowen’s reaction series~ pattern that illustrates the order in which minerals crystallize from cooling magma according to their chemical composition and melting point Chemical Stability of Minerals • ~ measure of the tendency of a chemical compound to maintain its original chemical composition rather than break down to form a different chemical • Depends on strength of bonds • Most resistant to weathering have the highest number of bonds between Si and O Physical Stability of Rocks • Rocks have natural zones of weakness that are determined by how and where the rocks form • Sedimentary~ weakness between layers • Metamorphic~ break in layers that form as the minerals align • Igneous~ have evenly spaced zones of weakness called joints that form as the rock cools and contracts