Rocks

How Rocks Form Using color, texture, and mineral composition, geologists can classify a rock according to its origin (how it was formed) Geologists classify rocks into three major groups: Igneous Sedimentary Metamorphic

Igneous Rocks

What is an Igneous Rock? Any rock that forms from magma or lava Three ways to classify Origin Texture Mineral composition

Origin May form ON or BENEATH Earth’s surface Extrusive rock – igneous rock formed from lava that erupted onto Earth’s surface Think “exterior” – meaning on the outside Example – Basalt Intrusive rock – igneous rock formed when magma hardened beneath Earth’s surface Think “interior” – meaning on the inside Example - Granite

Texture cont… Extrusive & Intrusive Rocks have different textures Intrusive = larger crystals/ coarse grained Extrusive = small crystals/fine grained or glassy

Mineral Composition Lava low in silica = dark colored rock Magma high in silica = light colored rock The formula for silica is: SiO2 (Silicon + Oxygen)

Uses of Igneous Rocks Largely used for tools and building materials Statues Bridges Paving streets Counter tops Good for cleaning pumice

Sedimentary Rock

What is a sedimentary rock? Sediment – small, solid pieces of material that come from rocks or living things may include shells, bones, leaves, stems Formed when sediment is deposited by water and wind Formed through a series of processes 1. erosion 2. deposition 3. compaction 4. cementation

1. Erosion Forces constantly weathering rocks on earth’s surface Heat, cold, rain, waves, grinding ice Forces form sediment In Erosion (1) running water, or ice loosen and carry away fragments of rock 1

2. Deposition Moving water, wind, or ice slow and deposit sediment into layers Sediment will sink to bottom Deposition (2) is process by which sediment settles out of the water or wind carrying it 2

3. Compaction Compaction (3) – the process that presses sediments together Thick layers eventually build up Heavy layers press down on layers beneath Weight of new layers further compacts sediments, squeezing them tighter together Layers remain visible in rock 3

4. Cementation While compaction occurring, minerals in rock slowly dissolve in water Cementation (4) – process in which dissolved minerals crystallize and glue particles of sediment together Dissolved minerals seep into the spaces between particles then harden 4

Types of Sedimentary Rock

Organic Sedimentary Rock Form where the remains of plants and animals are deposited in thick layers “organic” = once living

Chemical Sedimentary Rock Chemical rocks form when minerals are dissolved in a solution and crystallize

Uses for Sedimentary Rock Building materials Cement steel Tools Arrow heads

Metamorphic Rocks

What is a Metamorphic Rock? EVERY metamorphic rock is a rock that has changed its form HEAT and PRESSURE deep beneath Earth’s surface can change any rock into metamorphic rock (MR) When rock changes into MR its appearance, texture, crystal structure, and mineral content change Can form out of igneous, sedimentary or metamorphic rock

How can the rocks change? Collisions between Earth’s plates can push rock down toward heat of mantle Pockets of magma rising through crust provide heat Deeper rock is buried in crust, greater the pressure When under great pressure and temperature, minerals in rock can be changed creating a metamorphic rock

Types of Metamorphic Rock Foliated Rocks Grains arranged in parallel layers or bands May split apart along bands Example Shale  Slate

Types of Metamorphic Rock cont… Nonfoliated rocks Grains arranged randomly Do not split into layers Example Sandstone  Quartzite

Uses of Metamorphic Rock Building Flooring Roofing walkways Sculpture Use marble (Lincoln Memorial)

The Rock Cycle What is it? Forces deep inside the earth and at the surface produce a slow cycle that builds, destroys, and changes the rocks in the crust