Classifying Rocks Rocks -naturally occurring solid mixture of one or more minerals and organic matter -make up Earth’s crust

Geologists Texture -persons that collect and study rocks -observe texture and color -determine mineral composition -look and feel of rock’s surface -ex. smooth, glassy, rough, chalky

Grains -particles of minerals that give rock texture Size -large grains = coarse grained -small grains = fine grained

Shape of grains Pattern -wide range of different shaped grains -ex. fine pieces of sand, small seeds, smooth, jagged -grains form patterns -ex. flat layers, swirling patterns

-forms from cooling of molten rock Not visible Igneous Rock -no visible grain happens with fast cooling -forms from cooling of molten rock

The Rock Cycle The three main types of rock are formed during the rock cycle.

Igneous Rock -any rock formed magma or lava cooling -“igneous” means “fire” -made of mineral crystals -exception: different types of volcanic glass -hard, dense, and durable -used for tools & building materials -classified by: origin, texture, & mineral composition

Origin Extrusive Rock -where they are formed -two types: extrusive and intrusive -formed from lava erupting on Earth’s surface Fast cooling Small crystals -ex. Basalt and Obsidian

Intrusive Rock -formed when magma hardens below the surface Larger crystals Slow cooling magma -ex. Granite; forms core of many mountains

Sedimentary Rock -forms from other rock, plant, & animal remains pressed together -forms in layers

Sedimentary Rock Sediment -forms from particles being weathered, eroded, and deposited by water and wind are cemented together. -small, solid pieces of materials that come from rock or living things *other things include: shells, bones, leaves, stems

Erosion Deposition -running water or wind loosen and carry away fragments of rock -sediment settles out of water or wind carrying it -after deposited; compaction and cementation change the sediment

Compaction -process that presses sediments together -happens over millions of years -each year forms new layers compacted together -minerals in rock dissolve in water during compaction

Cementation -dissolved minerals seep into spaces -process where dissolved minerals crystallize and glue particles of sediment together

Types of Sedimentary Rock Clastic Rock -3 major groups: 1. clastic rock 2. organic rock 3. chemical rock -rock fragments are squeezed together -grouped by size of rock particles of which they’re made

Shale Sandstone -forms from tiny particles of clay -water deposits clay in very thin layers -feels smooth & splits easily -forms from sand on beaches, ocean floor, riverbeds -sand is compacted and cemented -easily absorbs water

Conglomerate & Breccia -mixture of fragments of different sizes -round edges are conglomerate -sharp edges are breccia

Coal Organic Rock -made from living things -remains of swamp plants buried in water -layers of decaying plants are squeezed -forms coal over millions of years

Limestone -formed from coral, clams, oysters, and snails whose shells pile up -shells are made of calcite -calcite cements shells together to form limestone

Chemical Rocks Uses of Sedimentary Rock -minerals dissolved in solution crystallize -also when seas evaporate and leave mineral deposits -ex. rock salt, gypsum -used in building materials -decorating outside walls of buildings -limestone used in cement

-formed when existing rock is changed by heat, pressure, or chemical reactions Meta (changed) Morphos (shape) -forms deep underground Metamorphic Rocks

How Metamorphic Rocks Form -collisions of Earth’s plates push rocks downward -deeper a rock is buried, the greater the pressure and temperature.

Classifying Metamorphic Rocks Foliated -classify by arrangement of grains -grains arranged in parallel layers or bands -thin, flat layering -may split apart along bands -ex. slate, gneiss

-grains arranged randomly -do NOT split into layers -ex. marble & quartzite -marble (formed from limestone) used for buildings and statues -slate (formed from shale) used for flooring, roofing, walkways, & chalkboards Nonfoliated Uses of Metamorphic Rock

Rock Cycle -continual process by which new rock forms from old rock material -Earth’s constructive and destructive forces, like plate tectonics, move rocks through cycle

Plate Tectonics -force that drives the rock cycle -push rocks back into the mantle where they melt and become magma -causes folding, faulting, & uplift that move the rocks -two types cause movement of rocks: 1. Subducting Oceanic Plates 2. Colliding Continental Plates