Rocks & Minerals

What's a Mineral?

Minerals are made up of one or more chemical substances called elements.  Eight basic elements make up 99% of the earths crust:  aluminum, calcium, iron, magnesium, oxygen, potassium, silicon and sodium.

These eight elements can combine in different ways producing more than 3500 different types of minerals.  Minerals can be metals, gemstones and may also form crystals exhibiting symmetrically arranged plane surfaces.  Quartz is the most common mineral on earth.

What is a Rock?

A rock is a solid material made up of a mixture of minerals.  Rocks form over millions of years as the earth undergoes changes.  Some rocks form as a result of natural activity within the earth, such as volcanoes and earthquakes.  They are also created by natural processes such as weather or erosion.  Over 600 different types of rocks have been identified.  The three basic types are: sedimentary, igneous and metamorphic.

Sedimentary Rock

Sedimentary rock is made of bits of other rocks mixed with mud, shells or plants.  Over millions of years the mixture setttles and hardens to produce this type of rock.  Often, these rocks start to form in areas where there were once lakes or oceans.  New layers of rock pile on top of the old and over time the water is squeezed out and the bits are cemented together.  For example, limestone is made up of old seashells, crushed together over a long period of time.

Igneous Rock

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Igneous means "Made by fire."  This type of rock forms deep inside the earth where temperatures can be greater than 1800 degrees Fahrenheit.  It is actually a mixture of molten (melted) rock and crystals, called magma.  From this hot liquid magma, two types of igneous rocks can form.  If the magma cools slowly and hardens below the surface of the earth it becomes plutonic rock.  The other type of igneous rock is volcanic rock.  Volcanoes push magma to the surface of the earth where it becomes lava.  Lava cools off and hardens becoming volcanic rock.  For example, pumice is a volcanic rock filled with tiny holes.  It is the only rock that can float in water.  The difference as to whether a rock will for crystals depends on the cooling process, the slower the better. 

Metamorphic Rock

Metamorphic rock is rock that has changed from one type to another.  Depending on heat and pressure in the earth a single type type of rock may turn into several different types of rocks.  For example, shale, which is a sedimentary rock made of mud or clay, can be changed to slate if the correct amount of heat and pressure is present.  This same rock exposed to extremely high temperature and pressure will become schist. For example, limestone made from crushed shells and exposed to intense heat and pressure will form marble.