Rocks are the building blocks of the Earth (at least the solid part!) and the rest of the solar system. Rocks are made of minerals and are generally inorganic (What is a mineral? Click HERE to go to the Minerals page!)


Scientists classify rocks as being of one of three types:

 Igneous, or cooled from molten rock

 Sedimentary, or built up and solidified in layers, and

 Metamorphic, or rocks changed by pressure, temperature, and other environmental conditions into another type (We often think of igneous and sedimentary rock being changed into metamorphic rock, but metamorphic rocks can also be changed into other types of metamorphic rocks.)


See THIS LINK or THIS LINK for examples of these types of rocks.


Wikipedia is acknowledged as a source for the definitions on this webpage.


This changing and building of rocks is called the rock cycle. A very nice description of it can be found at the Michigan DEQ site by clicking HERE.

Rock Sizes (Sedimentary) from HERE

Text Box: The common names for rock sizes are in everyday use, such as pebbles, sand, boulder, etc.  Yep, pebbles are just a type of small rock.

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What is a Rock?Text Box: What is a rock?  Is it the same as a stone?  Are pebbles just small rocks?
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Size, approx. diameter


> 10 inches


2.5 - 10 inches


0.12 - 2.5 inches


0.08 - 0.12 inches


0.007 - 0.08 inches


0.000015 - 0.007 inches


< 0.000015 inches