6th Types of Rock - MRS. BOGUSLAW'S WEBPAGEIntrusive Igneous Rock • Rock formed from the cooling and solidification of magma UNDER the Earth’s surface • Usually cools slowly,

Igneous RockInside the Restless Earth Chapter 2, Section 2

6th Grade Mrs. Boguslaw

Igneous Rock• Always begins as magma

• Magma can form when rock is heated, when pressure is released, or when rock changes composition

• Because magma is made of many different melted minerals, some minerals become solid before others do

Composition and Texture of Igneous Rock

• The longer it takes for magma or lava to cool, the more time mineral crystals have to grow

• Longer time —> bigger crystals —> coarser texture

• Less time —> smaller (or no) crystals —> finer texture

Intrusive Igneous Rock

• Rock formed from the cooling and solidification of magma UNDER the Earth’s surface

• Usually cools slowly, so has a coarse-grained texture with large crystals

Intrusive Igneous Rocks• Masses are named for sizes and shapes

• Batholith: largest

• Stock: smaller than batholiths

• Dike: sheetlike, cut across other previous rock units

• Sills: parallel to previous rock units

Extrusive Igneous Rock

• Rock that forms as a result of volcanic activity at or near the Earth’s surface, cools ABOVE the surface of the Earth

• Cools quickly, so usually fine grained with small or no crystals

Sedimentary RockInside the Restless Earth Chapter 2, Section 3

6th Grade Mrs. Boguslaw

Sedimentary Rock

• Forms at or near the Earth’s surface

• Forms without the extreme heat and pressure needed for igneous and metamorphic rock

• Most noticeable feature is strata - layers of rock

Origins of Sedimentary Rock• Wind, water, ice, sunlight, and gravity all cause rock to

weather into fragments called sediment

• Through erosion, this sediment is moved from one place to another

• During deposition, the sediment is deposited in layers

• As new layers of sediment are deposited, old layers are covered and compacted. Dissolved minerals form a natural cement that binds the sediment into sedimentary rock

Composition of Sedimentary Rock

• Classified by the way it forms

• Clastic sedimentary rock: made of fragments of rock cemented together by a mineral like calcite or quartz

• Chemical sedimentary rock: forms from solutions of dissolved minerals and water; rainwater dissolves rock and then it re-crystalizes

• Organic sedimentary rock: forms from the remains of once-living plants and animals; includes limestones and coal

Sedimentary Rock Structures

• Most important feature is stratification

• Stratification: the process in which sedimentary rocks are arranged in layers

• Strata are different depending on kind, size, and color of sediment

• Sedimentary rock can sometimes also show the motion of wind or water, called ripple marks

• Mud cracks can show areas that once had water that has dried up, like ancient lakes, streams, or shoreline

Metamorphic RockInside the Restless Earth Chapter 2, Section 4

6th Grade Mrs. Boguslaw

Origins of Metamorphic Rock

• The texture or mineral composition of a rock can change when its surroundings change

• If the temperature or pressure of the new environment is different from the one in which the rock formed, it will undergo metamorphism

Origins of Metamorphic Rock

• Contact Metamorphism

• Heated by nearby magma

• Does not melt the rock

Origins of Metamorphic Rock

• Regional Metamorphism

• Occurs when pressure builds up deep below other rock formations or when large pieces of the Earth’s crust collide

• Increased temperature and pressure causes rock to become deformed and chemically changed

Composition of Metamorphic Rock

• Metamorphism occurs when temperature and pressure inside the Earth’s crust change

• Minerals that were present when the rock first formed might not be stable in the new temperature and pressure conditions, so they change into more stable minerals

• Index minerals are minerals that form only at certain temperatures and pressures. They help us estimate the temperature, pressure, and depth at which a rock undergoes metamorphism

Textures of Metamorphic Rock

• Either foliated or non foliated

• Foliated Metamorphic Rock

• Mineral grains are arranged in planes or bands

• As heat and pressure increases, metamorphism continues

Textures of Metamorphic Rock

• Nonfoliated Metamorphic Rock

• Mineral grains are NOT arranged in planes or bands

• Commonly made out of one or only a few minerals

• Crystals change in size and composition during metamorphism

Metamorphic Rock Structures

• Deformation: a change in the shape of a rock caused by a force placed on it

• Folds or bends in rock are structures that indicate that a rock has been deformed