Rocks change over time
depending on how much pressure, weathering, and
they get. Pressure is the pushing down of top layers of
rock on lower layers of rock. We use football as an
example of this. Letís say that the football falls on the
ground and a player leaps on top of it. Think about the
player. He is just lying there, like a top layer.
He is feeling pretty good because he is the top layer.
Other players see this and jump on top of him, hoping to get the
ball away. First one player leaps on top, and the player with
the ball feels pressed down a little. Little by little, as
more players pile on top, he is pressed down so much that he
feels pushed into the ground and flattened. This is what
we mean by pressure.
Weathering is how the wind,
rain, snow, etc. affect the rock. Weathering isnít how one rain
storm affects a rock. Itís what lots of rain storms do to it
over a long, long time. Most of the time, weathering causes
bits and pieces of rock to separate from larger chunks and
washes them into streams and rivers. Erosion moves the pieces
of rock from place to place using gravity, running water, or
weathering. Erosion wears away rock over lots of time.
Rocks go through something
called the rock cycle. This is where rocks change over a lot of
time. Time, to a rock, is thousands and millions of years. A
rock can begin as one kind of rock and then change many times
before it is mined. Underground heat and the pressure we were
talking about, plus weathering can change rocks over millions of
There are three kinds of rocks:
and gemstones are mined in many different ways depending on how
close to the surface they are found. For example, if you found
a certain kind of rock at the bottom of streams or rivers, it
would be mined using
surface mining like
placer mining. If it
was about six feet underground, a different kind of surface
open pit mining would be used. In open pit mining,
layers of dirt are taken off the top until they get down to the
rock they want to mine. If it is deep in the Earth, different
underground mining are used. Mining companies use the
kind of mining that will get them to the rocks,
gemstones the cheapest. Mining companies will not mine for
anything that wonít make them money.
Each of the rocks
that we included on our site will include the following
information: What it is and where itís formed, how and where it
is mined, and what its uses are.
The rocks we cover
on this site are: