ROCKS AND THE ROCK CYCLE

WHAT IS A ROCK? A rock is mineral matter of variable composition, consolidated or unconsolidated, assembled in masses or considerable quantities in nature, as by the action of heat or water In other words, a bunch of minerals stuck together

WHAT IS A MINERAL? A natural, inorganic, crystalline solid that has a definite chemical composition. natural – not man-made inorganic – not made up of living or once living things crystalline solid – has a definite geometric shape (may be at the atomic level) definite chemical composition – will not vary ex. SiO 2

Scientist have identified more that 3000 different minerals Only 20 of those are common – called “rock- forming minerals” 10 of those make up 90% of the mass of the Earth’s crust

3 MAJOR ROCK TYPES Igneous rock – “from fire”, cooled and hardened lava Sedimentary rock – compressed and cemented sediments; broken from all rock types Metamorphic rock – “changed form”; heat, pressure, and chemical processes change existing rock

ROCK CYCLE The rock cycle is the natural process in which rocks transform from one rock type into another rock type over time, a type of natural recycling.

ROCK CYCLE

IGNEOUS ROCKS 2 major types based on where they form Intrusive Extrusive

TYPES OF IGNEOUS ROCK Intrusive igneous rock Forms from cooling and hardening magma within the earth Usually large crystals, cools slowly – coarse grained Intrudes into other rock types Extrusive igneous rock -Forms from cooling and hardening lava outside of the earth -Usually small crystals, cools rapidly - fine grained

EXAMPLES Intrusive Granite Basalt Extrusive Obsidian Pumice

IGNEOUS ROCK FORMATION

SEDIMENTARY ROCK Much of Earth’s surface is covered with sediments. Sediments are pieces of solid material that have been deposited on Earth’s surface by wind, water, ice, gravity, or chemical precipitation. When sediments become cemented together, they form sedimentary rocks.

WEATHERING AND EROSION The formation of sedimentary rocks begins when weathering and erosion produce sediments. Weathering is a processes that break rock into smaller pieces. After weathering, sediments are transported to new locations.

EROSION Erosion is the removal and movement of surface materials from one location to another. Four main agents of erosion are wind, moving water, gravity, and glaciers.

DEPOSITION Deposition occurs when sediments are laid down on the ground or sink to the bottoms of bodies of water. Sediments are deposited when transport stops. Largest particles settle out first, the next largest, and so on, so they are sorted into layers.

LITHIFICATION As more and more sediment is deposited in an area, the bottom layers are subjected to increasing pressure and temperature which causes lithification. Lithification includes physical and chemical processes that transform sediments into sedimentary rocks. Cementation occurs when mineral growth cements sediment grains together into rock.

FEATURES OF SEDIMENTARY ROCKS Bedding, or horizontal layering, is the primary feature of sedimentary rocks.

FEATURES OF SEDIMENTARY ROCKS Evidence of Past Life Fossils are probably the best-known features of sedimentary rocks. Fossils are the preserved remains, impressions, or any other evidence of once-living organisms. Ammonites mya

METAMORPHIC ROCKS Metamorphic rock forms when high temperature and pressure combine to alter the texture, mineralogy, or chemical composition of a rock without melting it. High temperatures from interior of Earth. High pressure from Weight of overlying rock Compressive forces caused by Plate Tectonics

METAMORPHIC TEXTURES Foliated rocks are characterized by wavy layers and bands of minerals. Nonfoliated rocks lack banded minerals. Composed mainly of minerals that form with blocky crystal shapes.

EXAMPLES Sedimentary rock limestone will undergo heat and pressure and become the metamorphic rock marble. Sandstone (sed) will become quartzite Shale (sed) → slate → schist → gneiss