RocksA rock is a mixture of one or more minerals. They are classified by

the way they are made.

Classifying RocksIgneous Rocks

Sedimentary RocksMetamorphic Rocks

Rock Cycle

Classifying Rocks

• When studying a rock sample, geologists observe the rock’s color, grain size, texture and determine its mineral composition.

• Using these characteristics, geologists can classify a rock according to its origin, or where and how it formed.

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.

Classifying Rocks: Texture

A rock’s texture is the size, shape and pattern of the rocks grains.

•Grain Size (fine or coarse grained)

•Grain Shape•Grain Pattern•No Visible Grain

Classifying Rocks: Mineral Composition

• Viewing the size and shape of crystals in the rock.

• Testing acid to determine if the rock includes minerals made of compounds called carbonates.

• Testing with a magnet to detect iron or nickel.

Classifying Rocks: Origin

Three major groups of rocks

• Igneous

• Sedimentary

• Metamorphic

Igneous Rocks

Igneous rocks are classified according to their origin, texture, and mineral

composition

•“Fire Formed”- melted rock material cools and solidifies (“freezing”) •Intrusive- rock formed inside the Earth •Extrusive- rock formed on the surface •Texture- the size of the crystals- NOT HOW IT FEELS

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).

Difference Between Intrusive and Extrusive Rocks

Intrusive Extrusive

Rocks INSIDE the Earth Rocks OUTSIDE the Earth

Plutonic Volcanic

Formed from magma Formed from lava

Usually dark Usually light colored

Usually dense Usually low density (light)

Mafic: magnesium & Iron Felsic: feldspar (aluminum)

Cools slowly Cools quickly

Large grains Small or no grains (fine or glassy)

Igneous rocks have “Intergrown Crystals”

• Intergrown...

• Not Intergrown...

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

Sedimentary RocksAny 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.

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.

From Sediment to Rock

• Erosion – running water or wind loosens and/or carries away small fragments

• Deposition – the process by which sediment settles out of the water or wind carrying it.

• Compaction – the process that presses sediments together. Often visible as layers.

• Cementation – process in which dissolved minerals crystallize and glue particles of sediment together.

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 & 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.

1. Types of Sedimentary Rock: Clastic

Clastic (fragmental) – made by compaction and cementation of sediments and are identified by the size of the fragments.

– Conglomerate has rounded fragments

– Breccia has angular fragments...

2. Types of Sedimentary Rock: Organic (Bioclastic)

• Organic or also called Bioclastic-

• Bio = life

• Clastic = fragments

• Made from accumulated shells (limestone) or plants (coal)

3. Types of Sedimentary Rock: Chemical

• Chemically formed rocks: evaporites

• Formed when water carrying minerals evaporates and leaves the minerals behind.

• Are identified by the minerals present (for example: halite hardness of 2.5)

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

Clastic Sedimentary Examples

• Shale

• Sandstone

• Conglomerates and Breccia

Organic Sedimentary Examples

• Coal

• Limestone

Chemical Sedimentary Examples

•

Metamorphic Rocks•Changed from a pre-existing rock

•Caused by extreme heat and/or pressure

•May result in a distorted structure

Any rock (igneous, sedimentary, or metamorphic) can become a metamorphic rock.

The term "metamorphic" means "to change form."

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.)

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.

Classifying Metamorphic Rocks

Geologists classify metamorphic rocks by the arrangement of the grains that make up the rocks.

Foliated – grains arranged in parallel layers or bands (thin flat layering). Slate is an example

Nonfoliated – mineral grains arranged randomly. Marble and quartzite are examples.

The word metamorphic means 'changed', so rocks that have changed are called metamorphic rocks.

Layers of sedimentary rocks are changed by underground heat or underground weight, or both. They have a layered or streaky appearance.

When limestone is heated and compressed it forms marble. Sandstone changes into a much harder rock called quartzite.

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

The Rock Cycle

The surface of the Earth is always changing and the three groups of rocks recycle from one kind to another.

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.

Rock Cycle

Hardness of some items:

• 2.5 Fingernail• 2.5–3Gold, Silver• 3Copper penny• 4-4.5Platinum• 4-5Iron• 5.5Knife blade• 6-7Glass• 6.5Iron pyrite• 7+Hardened steel file

Diamond Corundum Topaz

Quartz Orthoclase Apetite

Fluorite Calcite

Gypsum Talc

Interesting Trivia

Up to 100,000 tons of rock a year fall to earth from space. The largest meteorite in the world lies in the ground in Africa and weighs more than 60 tons.

Did you know that the diamond is the hardest natural

substance found on earth?

Did you know that quartz is one of the most common minerals on Earth?

Did you know that marble forms from metamorphosed carbonate rock, most usually limestone?

Did you know that basalt is the most common rock on Earth?

Did you know that breccia is a rock composed of generally large, sharp fragments cemented together?

Did you know feldspars make up more than 50% of the Earth's crust?

Did you know the first recorded use of turqouise dates back to 5000 BC in Mesopotamia, where people used the gemstone to make beads?

Did you know lapis lazul is treasured for its rich blue color and is often used in jewelry? Did you also know that ancient Eqyptians used powdered lapis lazul as eye shadow?

Did you know jade because of it's toughness has been used for many cultural things like hammers, fish hooks, and stone axes.

Did you know that rubies are one of the most popular gemstones today.

Did you know that the first geologist on the moon was Harrison Schmitt who was part of the Apollo 17 mission? From the rock samples he collected, scientists have been able to learn many things about the moon.

Did you know that the Earth is approximately 4.8 billion years old?

Did you know that gold is so soft and easily worked that you could roll an ounce of it into a hair-thin wire 50 miles long?

Did you know that the biggest pure-gold nugget was found in Australia in 1869 and weighed 156 pounds?

Did you know that platinum is so rare that two million pounds of ore may contain only one pound of metal?

Did you know that geodes are dull balls of igneous or sedimentary rock on the outside, but contain beautiful crystals on the inside?

Did you know that meteorites, rocks from space, help scientists learn about the solar system and are very valuable, too?

Did you know that the Taj Mahal built between 1632 and 1654 in India is made entirely out of marble?

Here are some proverbs or "rock sayings" that have been handed down through the years.

• Your head is as hard as a rock. • I am between a rock and a hard place. • He is just a chip off the old rock. • Your head must be full of rocks. • Build your house upon a rock, and not shifting

sand. • She has a heart of stone. • To soften rocks, or bend a knotted oak • Rock of ages, cleft for me • Water continually dropping will wear hard rocks

hollow. • It was founded upon a rock.

Now for some fun! Here are some rock "puns“

• What does a rock want to be when it grows up?

• What do you call a dog who collects rocks?

• What do you do to a baby rock?

• What is a rock's favorite kind of music?

• Where do rocks sleep?

• How do rocks wash their clothes?

• What is a rock's favorite transportation?

• What is a rock's favorite cereal?

• Where is a rock's favorite golf course?

• What is a rock's favorite television show?

Answers

• A Rock Star

• A Rockhound

• Rock it

• Rock 'N Roll

• Bedrock

• On the rock cycle

• A rocket

• Cocoa Pebbles

• Pebble Beach

• "Third Rock from the Sun"

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