Topic 3B – Rocks and the Rock Cycle Ms Cooke Earth Science

Rocks  Rocks are mixtures of minerals, organic material, glasses, and fragments of other rocks.  A single-mineral rock is both a rock and a mineral.  It has the mineral’s definite composition and properties.  i.e. Rock Salt, Rock Gypsum, Dolostone

The Types of Rocks  Igneous – Mostly formed deep under the Earth’s surface, when magma cools and hardens. A small percent form from lava.  Sedimentary – Weathering and Erosion (the breakdown and transport of rocks) such as wind or water break down all rock types into fragments, called sediments. These sediments become compressed and cemented together forming sedimentary rocks.  Metamorphic – From forces such as heat and pressure, as well as chemical processes, that act on existing rocks, altering them to a new form.

The Rock Cycle  The Rock Cycle illustrates the changes the rock types undergo over time.  Some rocks have been through the cycle many times  We are recycling rocks!

The Rock Cycle – ESRT Pg 6

Rock Recycling

IGNEOUS ROCKS Rocks formed by MELTING of existing rock to form a new rock

IGNEOUS ROCKS  IGNEOUS ROCKS come from molten rock (or magma)within the earth, or from lava (extruded from the surface).  The kind of Igneous Rock formed depends on what material was melted, and THE RATE of cooling.  Igneous rocks are classified based on their mineral composition and texture!

IGNEOUS ROCK TEXTURE Intrusive (Plutonic)  Form deep within the crust - magma  Cool slooooooowly  Have LARGE (visible) crystals  Coarse to Very Coarse Grained  1mm to 10+ mm Extrusive (Volcanic)  Form at the surface – lava  Cool fast  Have small to microscopic crystals  Fine Grained to Glassy  Less than 1 mm

IGNEOUS ROCK TEXTURE  Extrusive rocks may also be VESICULAR  Have Gas Pockets  Due to gases escaping from the lava  If no gasses – Non-Vesicular

Igneous Rock Mineral Composition Felsic Mafic Intermediate

Classifying Igneous Rocks ESRT Pg 6

Sedimentary Rocks Rocks formed from compacting and cementing rock particles or fragments (sediments)

Sedimentary  Sedimentary Rocks form when rock fragments, organic materials, or minerals that have precipitated out of solution are compacted and cemented together.

Main Process of Formation  Converts loose sediment into sedimentary rocks  COMPACTION – Due to the layering by deposition the sediment is squeezed and the size of the pore space (air pockets) is reduced.  CEMENTATION – Sediments are “glued” together by the minerals that are deposited by water.

Main Process of Formation

Sedimentary Rock Types Clastic  Formed by the deposition of sediments which are then compacted and cemented together.  Classified by Size of Sediments Crystalline  Formed by Minerals that we once dissolved in water. Some form when minerals precipitate out of water.

Sedimentary Rock Types Clastic – Sediment Sizes ParticleSize Boulder25.6 cm and over Cobbles6.4 cm – 25.6 cm Pebbles0.2 cm – 6.4 cm Sand0.006 – 0.2 cm Silt cm – cm ClayLess than cm

Sedimentary Rock Types Clastic – Sediment Sizes ParticleSize Boulder25.6 cm and over Cobbles6.4 cm – 25.6 cm Pebbles0.2 cm – 6.4 cm Sand0.006 – 0.2 cm Silt cm – cm ClayLess than cm

Clastic – Conglomerate and Breccia  CONGLOMERATE – have larger sized rounded particles or fragments cemented by sand, silt, or clay.  BRECCIA – similar to conglomerates, but with angular particles.

Clastic – Sandstone  SANDSTONE – is composted of sang grains that have been cemented  Largely composed of quartz  Many types are porous  DOES NOT REACT WITH ACID

Clastic – Shale and Siltstone  SILTSTONE – consists of clay sized particles that are cemented and compacted  SHALE – consists of silt sized particles Shale is VERY fine, usually dark colored (green, black, or red). Often splits into thin, flat pieces. Siltstone is fine, but doesn’t split into flat sheets. Also called mudstone.

Clastic – Bioclastic – Organic Fragments COAL  Composed of mostly CARBON  Black LIMESTONE  Composed of mostly Calcium Carbonate  CaCO 3  BUBBLES WITH ACID Forms when living things are buriedbefore they can decay

Sedimentary Rock Types Crystalline  Formed by Minerals that we once dissolved in water. Some form when minerals precipitate out of water.

Sedimentary Rock Types

Metamorphic Rocks Changing a Rock’s Chemical Structure by Heat and Pressure

Changing the Chemical Structure  Usually formed deep within the Earth’s Crust  Formed by Heat and Pressure  Causes rock’s chemical structure to change

Metamorphic Types REGIONAL  The process by which heat and pressure deep under the surface change a LARGE area of rock  Mountain Building CONTACT  Process in which rocks come in contact with magma, causing changes to occur  Small area around magma intrusion

Grades of Metamorphism  Low Grade – Low temperature and pressure (just enough to change).  Slate and Phyllite – Small crystals, fine grained  Intermediate – Higher temperature and pressure than low grade  Schist – larger mica crystals  High Grade – Highest Temperature and pressure possible without melting  Gneiss – Crystal alignment into bands

Grades of Metamorphism

Foliation and Banding  Foliated Rocks – When metamorphism results in the alignment of crystals into layers.  Schist  Banding – When crystals grow in alternating light and dark layers  Gneiss  Non-foliated – No alignment of crystals or layering.  Marble

Foliation and Banding