The Rock CycleCh 10

Rocks and the Rock Cycle

• Magma is the parent of all rocks

• Three Major types–Igneous “from fire”

–Sedimentary

–Metamorphic “Changed Form”

The Rock CycleSeries of processes in which rock

changes from one type to another and back again.

Igneous Rocks• Forms as Magma cools

- Igneous Rock Structures

• Below crust is Intrusive

• Intrusions- underground rock masses

• Batholiths over 100 square kilometers

• Stock under 100 Km2

• Laccolith-domed lake of rock, forces up small mountain ranges

• Sill layer of rock formed between other layers

• Dikes- magma forcing it self across layers

• Extrusions

• Above Crust is Extrusive

• Volcanic neck-lava remains from interior of volcano

• Lava plateau-lava flows out of cracks and covers land

• Texture of igneous rock–Slow cooling allows large

(course) crystals to form

–Extrusive rock will have very small crystals

PorphyryPorphyry is a mix of large and

small crystals

• Rapid cooling may result in a glassy appearance obsidian, or may trap gas bubbles, pumice

Obsidian

Three Families of Igneous Rock

• Granite light colored or felsic (silica) orthoclase feldspar, quartz, hornblende, and mica

Granite

Diorite medium colored, plagioclase feldspar, hornblende, augite and biotite. Little quartz

–Basalt dark or mafic (Iron) plagioclase feldspar, and augite

Basalt

Sedimentary RocksSedimentary rocks are formed when sediments undergo compaction (pressure) and cementation (glue)

3 typesClastic, Chemical, Organic

• Clastic- sediments (small pieces) are carried away by wind, water or ice and left as deposits

• These deposits then undergo cementation and compaction

• Chemical- rocks form from minerals that have been dissolved in water

• Organic- rocks are the remains of living things

Clastics• Clastics are identified by the size of

their sediment

• Conglomerate- rounded. pebble size

• Breccia- angular pebble size

• Sandstone- sand sized particles

• Shale- clay particles

• Conglomerate- rounded. pebble size

Conglomerate

• Breccia- angular pebble size

Breccia

• Sandstone- sand sized particles

Sandstone

• Shale- clay particles

Shale

Chemical• Some minerals precipitate due to a

change in temperature, limestone

• Evaporates-left behind when water evaporates gypsum, halites

Limestone

Rock salt and Gypsum

Organic• Coal-formed from plants being buried

then compacted

• Organic limestone-shells from clams, coral, oysters and plankton form limestone

Coal

Organic Limestone

Features• Stratification-layer representing

conditions when formed. cross-bedding

• Ripple marks and mud cracks

• Fossils

• Concretions precipitated minerals build up around existing rocks

Concretion

Metamorphic rocks• Rock may change because of

exposure to heat and pressure, or have minerals dissolved or added

• Two types metamorphism– Contact (direct)

–Regional (Barrovian)

Classification• Foliation

–metamorphic rock has visible stripes

• Can be formed when crystals are pushed into parallel bands or minerals of different densities separate into bands

Schist

• Banding–Minerals form into district lines,

–Requires more heat and pressure than foliation

Both take flat minerals like mica and force them into bands

Gneiss

Example of formation

• Slate, schist and gneiss

• Slate comes from shale

• More heat and pressure turn slate in schist

• Schist transforms into gneiss

•Unfoliated •Have no bands•Formed from rocks with one mineral• Quartzite formed from sandstone• Marble formed from limestone

Slate

Quartzite

Marble

Images from about.geology.com