The Rock Cycle

Rocks are the most common material on Earth. They are naturally occurring aggregates of one or more minerals.

Rock divisions occur in three major families based on how

they formed: igneous, sedimentary, and

metamorphic. Each group contains a collection of rock

types that differ from each other on the basis of the size, shape, and arrangement of mineral

grains. The rock cycle is an illustration that is used to explain how the three rock types are related to

each other and how Earth processes change a rock from

one type to another through geologic time. Plate tectonic movement is responsible for the recycling of rock materials and is the driving force of the

rock cycle http://www.youtube.com/watch?v=CvDw07iYaJQ

There are places on Earth that are so hot that rocks melt to form magma. Because magma is liquid and usually less dense than surrounding solid rock, it

moves upward to cooler regions of the Earth. As the magma loses heat, it cools and crystallizes into an igneous rock. Magma can cool on the Earth's

surface, where it has erupted from a volcano (extrusive rock) or under the Earth's surface, where it has intruded older rocks (intrusive rock).

The composition of magma is limited to the eight common elements of the earth's crust. These elements combine within a melt to form silicate minerals, the most common minerals of igneous rocks. These silicate minerals include feldspars (plagioclase feldspar, potassium feldspar), quartz, micas (muscovite, biotite),

pyroxenes (augite), amphiboles (hornblende), and olivine. These minerals make up over 95% of the volume of the common igneous rocks, making igneous rocks

easy to identifiy.

Igneous Rocks

Extrusive igneous rocks form when magma reaches the Earth's surface a volcano and cools quickly. Most

extrusive (volcanic) rocks have small crystals. Examples include basalt, rhyolite, and andesite.

Intrusive, or plutonic, igneous rocks form when magma cools slowly below the Earth's surface. Most

intrusive rocks have large, well-formed crystals. Examples include granite, gabbro, and diorite.

Igneous rocks are recognized by: the interlocking texture of the grains the presence of vesicules (holes) in

extrusive igneous rocks may be dark-colored and heavy may display two grain sizes, one

much larger than the other

Igneous (means "fire")

Igneous rock was once hot liquid inside the earth. Rock that erupted from volcanoes and cooled on the surface is called extrusive igneous rock. Igneous rock that cooled more slowly inside the Earth is called intrusive. Apache Tear and the Hawaiian Islands are mainly igneous rock.

Any rock (igneous, sedimentary, or metamorphic) exposed at the Earth's surface can become a sedimentary rock. The forces of wind, rain, snow, and ice combine to break down or dissolve (weather), and carry away (transport) rocks exposed at the surface. These particles eventually come to rest (deposited) and become hard rock (lithified).

Sedimentary rocks tell us what the Earth's surface was like in the geologic past. They can contain fossils that tell us about the animals and

plants or show the climate in an area. Sedimentary rocks are also important because they may contain water for drinking or oil and

gas to run our cars and heat our homes.

Sedimentary Rocks

Clastic sedimentary rocks form by weathering processes which break down rocks into pebble, sand, or clay particles by

exposure to wind, ice, and water. Clastic and nonclastic sedimentary rocks are the only members of the rock family

that contain fossils as well as indicators of the climate (ripple marks, mudcracks and raindrops) that was present

when the rock was formed.

Conglomerate

Breccia

Sandstone Shale

Clastic Sedimentary Rocks

Nonclastic sedimentary rocks form from chemical reactions, chiefly in the ocean. Nonclastic and clastic sedimentary rocks are the only members of the rock family that contain fossils as

well as indicators of the climate that was present when the rock was formed. Nonclastic sedimentary rocks are named

according to the mineral present. Limestone

Nonclastic Sedimentary Rocks

Rock salt

Rock gypsum

Chert

Sedimentary rocks are recognized by: grains cemented together

the presence of fossils light-colored and light weight

may display interlocking grains but is very light weight

Sedimentary

Sedimentary rock which was formed out of soil, silt, sand, seashells, bits of pieces of everything - fossils. The tiny bits settled and built up in thick layers. Minerals from water seeped into the spaces between the particles and bonded

them into solid rock. The Grand Canyon is made up of sandstone, limestone, and shale which are all sedimentary rocks.

• Fossil Shark Teeth Found at Aurora in the Pungo River, Yorktown, and James City • Aurora - PCS Phosphate Mine, Aurora, NC

Any rock (igneous, sedimentary, or metamorphic) can become a metamorphic rock. If rocks are buried deep in the Earth at high

temperatures and pressures, they form new minerals and textures all without melting. If melting occurs, magma is formed, starting the rock cycle all over

again. Geologists can learn the following about the Earth from the study of

metamorphic rocks: the temperature and pressure conditions (metamorphic environment) in

which the rock was formed the composition of the parent, or original un-metamorphosed, rock.

aids in the interpretation of the plate tectonic setting in which the metamorphism took place

aids in the reconstruction of the geological history of an area. The term "metamorphic" means "to change form." Changes in the

temperature and pressure conditions cause the minerals in the rock to become unstable so they either re-orient themselves into layers (foliation) or

recrystallize into larger crystals, all without undergoing melting.

Metamorphic Rocks

Foliated Metamorphic Rocks

Foliated metamorphic rocks are formed within the Earth's interior under extremely high pressures that are unequal, occurring when the pressure is greater in one direction than in the others (directed

pressure). This causes the minerals in the original rock reorient themselves with the long and flat minerals aligning perpendicular

to the greatest pressure direction. This reduces the overall pressure on the rock and gives it a stripped look.

      

Foliated metamorphic rocks are identified on the basis of their texture:

Slate Phyllite Schist

Gneiss

Slate Phyllite

Schist

Gneiss (nices)=

Foliated Metamorphic Rocks

Nonfoliated Metamorphic Rocks

Nonfoliated metamorphic rocks are formed around igneous intrusions where the temperatures are high but the pressures are relatively low

and equal in all directions (confining pressure). The original minerals within the rock recrystallize into larger sizes and the atoms become more tightly packed together, increasing the density of the

rock.

Nonfoliated metamorphic rocks are identified on the basis of their

composition:

    

Quartzite

    

Marble

Quartzite

Marble

Nonfoliated Metamorphic Rocks

Metamorphic rocks are recognized by: the interlocking texture of large grains

foliation (layering) banded light and dark colors

"ching" sound instead of a "chunk" sound when tapped

Metamorphic(means to "change")

rock used to be igneous or sedimentary rock that was changed by heat or pressure or both. The Appalachian Mountains including the Blue Ridge are

mainly metamorphic rock with a little igneous rock.

How large is the lifetime supply of minerals for the average person?

At today's level of consumption, the average newborn infant will need a lifetime supply of 800 pounds of lead, 750 pounds of zinc, 1,500 pounds of copper, 3,593 pounds of aluminum,

32,700 pounds of iron, 26,550 pounds of clays, 28,213 pounds of salt, and 1,238,101 pounds of stone, sand, gravel, and

cement.

What are the oldest rocks on earth?

The oldest rocks on Earth found so far are the Acasta Gneisses in northwestern Canada near Great Slave Lake

(4.03 billion) and the Isua Supracrustal rocks in West Greenland (3.7 to 3.8 billion).

Rocks nearly as old are also found in the Minnesota River Valley and northern Michigan (3.5-3.7 billion years), in

Swaziland (3.4-3.5 billion years), and in Western Australia (3.4-3.6 billion years).

Why do some rocks glow in the dark?

Some minerals fluoresce under UV light due to impurities known as activators. The activator absorbs ultraviolet radiation,

and in reaction emits a combination of visible light (color). Sometimes the activator electrons get stuck in their high-

energy state and the mineral will continue to glow after the UV light is switched off. This is called phosphorescence. Common

minerals that fluoresce are Calcite and Fluorite.

What is the largest diamond?

The largest diamond every found was discovered on January 26, 1905 at Premier Mine in south Africa. The Cullinan diamond weighed 3,106 carats, about 1 1/3

pounds. It was cut into 9 stones, one of which is the worlds second largest diamond, The Star of Africa. It is set in a

scepter and is part of the British Crown Jewels. 

The Hope: AT 45.52 carats

The Star of Africa

The Allnatt: At a 101.29 cts

Strawn-Wagner Diamond" is the most perfect diamond the American Gem Society (AGS) ever certified

What makes the different colors in fireworks?

Mineral elements taken from Earth provide the colors for fireworks. Strontium yields deep reds; copper produces blue; halite yields yellow;  iron filings and

charcoal pieces produce gold sparks; barite creates greens; magnesite, zircon, and rutile are used to produce a silvery white color; Bright flashes and

loud bangs come from aluminum powder.

Each of the three basic rock types was used in the construction of the Lincoln Memorial in Washington DC; igneous granite is found in the base and lower steps of the memorial, the floor and statue of President Lincoln are made of metamorphic marble, and the interior columns and walls are composed of sedimentary limestone.