Rocks 101

What is a Rock?

A rock is made up of many different mineral crystals/fragments. A rock can be classified into three types:

A. Igneous Rocks

B. Sedimentary Rocks

C. Metamorphic Rocks


How are different rock types formed?

Rocks are formed through a system that constantly forms, deforms, transforms, destroys, and reforms them. This system can be best understood by looking at a Rock Cycle Chart. Here you can see that any one rock type can be transformed into either of the other two rock types or recycled within its own group.


If minerals have properties; do rocks also have properties?

The properties that a rock exhibits are our main clues to identify them. All three types of rocks exhibit different properties. However, there are some properties that are common among all three types of rocks. These properties are form, color, composition, and texture.


How do you tell the difference between an Igneous, Sedimentary, and Metamorphic Rocks?

As stated before different rock types have different properties. However also remember that because there are some common properties among all rocks that when identifying them you have to use many properties.

Igneous Rocks commonly have a composition consisting of olivine, pyroxene, and feldspar crystals. They also may exhibit have a ropy type of banding, this is caused by cooling lava.

Sedimentary Rocks are generally layered and exhibit a clastic texture. They also preserve fossils and other organic remains. Common places that sedimentary rocks occur at are river beds, deltas, beaches, sand bars, and extensive flat layers (depositional environments).

Metamorphic Rocks have textures such as folds, fractures, faults, and foliation. Foliation is the most common indicator of a metamorphic rock. Often the composition consists of garnet, tourmaline, and mica. It is a metamorphic rock if it contains serpentine, epidtoe, graphite, galena, or sphalerite because these minerals only occur in metamorphic rocks.


Rock Flow Charts
(requires at least Acrobat 4 to open)

Igneous, Sedimentary, or Metamorphic Flow Chart Part 1

Igneous, Sedimentary, or Metamorphic Flow Chart Part 2

Rock Cycle Flow Chart

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