The Earth is made up of rocks and minerals.
    
The core of the Earth is molten rock.
 
On the outside, there's a crust. Within this crust, the most abundant elements (by mass) are oxygen and silicon.
 
Sometimes this crust is covered by water, sand, soil or ice.
 
But if you dig deep down you will always find solid rock (bedrock).
 
Bedrock varies by age depending on where you are.
 
In the Finger Lakes region of New York, for example, the most common bedrock dates back to the Devonian era (approximately 408-350 million years ago).
 
Rocks and minerals are not the same.
 
 
Rocks vs. Minerals
 
The main difference between a rock and a mineral is that a mineral is the same substance all the way through -- while a rock is made up of different substances.
 
A web site called www.RocksforKids.com has this explanation.
 
A rock is like a chocolate-chip cookie.
 
Why? It's because both are made up of different things.
 
In a chocolate chip cookie, those things are flour, butter, sugar and chocolate.
 
In a rock, those things are minerals.
 
 
Minerals
 
As we said, a mineral is the same substance all the way through -- like a gold nugget or a diamond (bling, bling).
 
There are about 3000 different minerals.
 
Some are composed of just one element or chemical. Others are made up of a combination of elements or chemicals.
 
Minerals are often found in crystal form -- which means that they grew in exactly the shape specific to that mineral. Most crystals were formed millions of years ago when the liquid rock inside the earth began to cool and harden.
 
Geologists can identify a mineral by the shape of its crystal.
 
A mineral is also identified by its hardness -- which means its resistance to scratching. This hardness is most closely related to that mineral's internal arrangement of atoms.
 
Hardness is measured by something called Moh's Mineral Hardness Scale. This is a scale adapted 200 years ago by mineralogist Frederick Moh from a test regularly used by Austrian miners.
 
 
The Moh Scale
 
On the Moh scale, minerals are ranked in order of their increasing hardness:

1 = Talc
2 = Gypsum
3 = Calcite
4 = Fluorite
5 = Apatite (Fluorapatite)
6 = Feldspar
7 = Quartz
8 = Topaz
9 = Corundum
10 = Diamond

A mineral can only be scratched by a mineral or other object with a higher Moh score.
 
Here is the approximate hardness of some common everyday objects:

2.5 Fingernail
3.5 Copper Penny
4.5 Iron Nail
5.5 Glass
6.5 Steel File

This means, for example, that glass can be scratched by quartz but not by calcite.
 
For a thorough, illustrated discussion of rocks and minerals, click:
 http://www.rocks-and-minerals.com
 
 
Back to Rocks
 
There are many different names for rocks. Often, these names refer to size. Here are a few of them:

• boulder a large rock, taller than a person
   
• river rock a round, smooth rock found along the edge of a fast-flowing river
   
• stone a medium sized rock you could hold in your hand
   
• pebble so small you could hold it with two fingers; any large rock can be weathered down to the size of a pebble
   
• sand made up of tiny pieces of rock
   
• grain tiny, the size of a grain of rice or smaller
   
• dust really fine powder mixed in with sand or soil
   
• mountain a huge, giant hunk of rock still attached to the Earth's crust .

 
Rock, Soil, Plants
 
When rocks break down into smaller pieces, they become sand. This sand is found everywhere, not just at the beach.
 
It is made up of the same minerals that the original rocks were.
 
When this sand combines with decomposing plants and animals, it becomes soil (also called clay, silt, mud, dirt, topsoil, potting soil, humus or dust). But no matter what you call it, it's important -- because soil is what plants grow in.
 
And without plants, there would be no life.
 
 
The Rock Cycle
 
Rocks are constantly being formed, worn down and formed again.
 
This is known as the rock cycle.
 
Within this cycle, rocks go through three different stages. This gives us three different kinds of rock:

Igneous
Sedimentary
Metamorphic

Igneous Rocks

Igneous means made from fire or heat.
 
Igneous rocks are created when volcanoes erupt and the liquid rock inside the Earth rises to the surface and flows out.
 
When the rock is liquid and still inside the Earth, it's called magma.
 
Once it flows out of the volcano, it's called lava.
 
When it cools and hardens, it's called lava rock, obsidian or pumice (depending on how it looks).
 
If it's glassy, smooth and black, it's called obsidian.
 
If it's light and full of air pockets, it's called pumice. Pumice exhibits a definite pyroclastic (volcanic) texture. It's the only rock that floats.
 
There are different kinds of igneous rock. Here they are, along with the minerals they're made up of:

Granite or rhyolite (quartz, low-temperature feldspar and mica). If you were asked to identify a rock with a mineral composition of quartz, potassium feldspar, plagioclase feldspar, biotite and amphibole, it would be rhyolite.

Diorite (feldspar and one or more dark minerals, with feldspar dominant)

Gabbro (feldspar and one or more dark minerals, with the dark minerals dominant)

Peridotite (iron)

Pegmatite (coarse-grained granite with large crystals of quartz, feldspar
and mica)

Igneous rocks can also be classified as either Felsic or Mafic.

Felsic rocks are composed mainly of light-colored materials -- such as mica,
quartz and feldspar.

Mafic rocks are composed chiefly of dark colored materials containing iron and magnesium.


Sedimentary Rock

When mountains are worn away due to erosion, little bits of rock (sediment) end up in the streams and rivers that flow down from the mountains.

Over time, these sediments settle to the bottoms of the rivers and the lakes -- and the oceans they flow into. The most deposition (depositing of sediment) is likely to occur at the top of a steep slope in a streambed.

As layers and layers of sediment build up, pressure on the protolith (the original material) increases. This pressure turns the sediment into sedimentary rock.

If this process takes place at low temperatures and pressures, it's called diagenesis. Higher temperatures and pressures cause metamorphosis (see below).

Sandstone, shale and jasper are sedimentary rocks.

Sedimentary rocks often have fossils in them.

That's because animals and plants died and got mixed up in the sediment.

When this happens, sedimentary rocks turn into carbon -- which is how we get coal, oil, natural gas and petroleum.

Rocks with lots of fossil shells in them were frequently created in shallow ocean bays.

There are 6 main kinds of sedimentary rock:

Conglomerate rock (rounded rocks -- pebbles and boulders -- cemented together)

Sandstone (grains of sand cemented together)

Shale (clay that has been hardened and turned into rock; shale often breaks apart in large, flat sections)

Limestone (made of calcium carbonate and/or microscopic shells; limestone contains many fossils)

Gypsym (common salt or Epsom salt found where sea water is precipitated or evaporates)

Porphory Rock (jagged bits of rock cemented together)

Metamorphic Rock

Metamorphic rocks are rocks that have changed or morphed.
 
"To morph," as you know, means to change form -- like the Mighty Morphin' Power Rangers used to do. And some Superheroes still do.
 
Metamorphic rocks were originally either igneous or sedimentary rocks that have changed because of the movement of the Earth's crust. High temperatures and pressures are involved -- much higher than the temperatures and pressures involved in the diagensis that creates  sedimentary rock.
 
There are two kinds of metamorphic rock: foliated and non-foliated.
 
Foliated metamorphic rock has different layers or banding. Slate is a good example. Slate is usually the product of regional metamorphosis. It is morphed from shale and splits apart into smooth slabs.
 
Non-foliated metamorphic rock is not layered. Marble is a good example -- it
is morphed from limestone.
 
In some quizzes you may be asked to identify various sorts of rocks. A web site designed specifically to help you with this is:
http://www.lethsd.ab.ca/mmh/grade3c/Gr3Web/rocks_miner/indentify_rocks/identify_rocks1.htm 

Experiments for Home and Classroom

Rocks are constantly being formed, worn down and formed again as they go through the Rock Cycle to become either Igneous, Sedimentary or Metamorphic. This fascinating web site from the British Broadcasting Company offers dozens of Rock Cycle experiments. Visit the site and click on the specific part of the illustration that shows the experiment you'd like to perform. This is a terrific site! Click:
http://www.bbc.co.uk/schools/gcsebitesize/chemistry/changestoearthandatmosphere/0rocksrev1.shtml 

The surface of the Earth is made up of rocks and minerals -- which are not the same thing. A mineral is the same substance all the way through, like gold or diamonds. A rock is made up of different substances. One of the ways geologists identify minerals is by the shape of their crystals. In this simple experiment (appropriate for all ages with parental consent), students actually grow crystals themselves. Click:
http://www.yesmag.ca/projects/crystal_gardens.html 

In this activity, students learn five basic steps to perform when identifying a mineral. Read the instructions and then click "Start Mineral Identification:"
http://www.minsocam.org/MSA/K12/properties/minid/mineralid.html

This "Hot Rock" experiment combines rock identification with a study of energy absorption. Since it was designed for younger students, teachers should scroll down to "Teacher Information" for suggestions on how to make it more challenging for 10th through 12th graders. The basic Hot Rock web site is:
http://web.stclair.k12.il.us/splashd/hrockexp.htm 
Student Instructions begin at:
http://web.stclair.k12.il.us/splashd/HotRocks.pdf

This is an experiment in mineral triboluminescence (pronounced TRY- bo - lumen - essence). Luminescence means light or glow. Triboluminescence is light produced by pressure, friction, or mechanical shock. In this experiment, students learn about triboluminescense by rubbing two hand-sized quartz crystals together in a darkened room -- which is not as simple as it sounds. For complete instructions, click:
http://rockhoundingar.com/quartz/experiments.html 

for Students, Parents and Teachers

Now let's do Practice Exercise 3-4 (top). Choose printer friendly or online exercises. Printer friendly version requires the Adobe Acrobat Reader 5. Click HERE to obtain a free copy.