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The Rock Cycle

Rocks don't form into the three types of rocks and stay there.  The Earth is constantly changing and in motion.  The rock cycle demonstrates how a rock can start out as one type and change into another.

Any rock can be taken through the cycle.  For example, I will start with granite (remember, granite is intrusive). 

As granite is exposed on the Earth's surface it starts to weather.   Rain and snow and wind all work on breaking the granite down into smaller pieces.   As the granite is weathered, the minerals that make up granite-quartz, feldspar, and mica all break down out of the rock. 

The mica and feldspar turn to clay minerals and are deposited close to the granite.  The quartz is much stronger.   It finely ends up along rivers and lakes or oceans as sand.  The sand builds up thick layers so the sand on the bottom becomes sandstone.  As the sandstone is pressurized it becomes quartzite. 

So now lets say the quartzite is exposed to the surface due to weathering.  As the quartzite starts to weather, it will become sandstone and can start the process over again.  Or the quartzite can be buried in the Earth's crust and go into the mantle to become molten rock which can become granite again.

Not all rocks go through the rock cycle.  And not all rocks go through all the stages.  For example:  a sedimentary rock may weather again and become a new sedimentary rock.

 Suggested Classroom Project

Collect three(3) of each type of rock:  igneous, metamorphic & sedimentary.  Explain how each type of rock forms.

Bonus Question:  What is the difference between intrusive and extrusive igneous rock?

These rocks can be displayed in a number of ways.  Glue rocks to the bottom of a cardboard box or put each rock in its own plastic bag and label.   We recommend keeping track of the locality where each rock is found.  A specimen is much more interesting and scientifically more valuable if the locality is known.

For additional questions, please contact me at rockshop@rocks4u.com.  Rick Dalrymple

Suggested Classroom Project

Check out Ms. Stupelli's 5th Grade Rock Tumbling Project at:

rocktumblers.blogspot.com/2005_12_10_rocktumblers_archive.html

rocktumblers.blogspot.com/2005_12_19_rocktumblers_archive.html

Suggested Classroom Project

What are UV Minerals?  Minerals that fluoresce under Ultra Violet Light.  See for yourself!

Minerals under Ordinary Light

Minerals under Short Wave UV Light