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Rocks are solid clumps of minerals that make up the Earth's crust.  A mineral is a substance, which has a definite chemical composition and distinctive physical properties such as hardness, crystal structure and luster.  Some examples of minerals are quartz, pyrite, gold and copper. There are three different ways in which rocks are created, so geologists usually classify rock according to how it was made. The three main types of rocks- igneous, sedimentary and metamorphic.

Igneous

Igneous rocks originate from magma, or liquid rock, from within the earth.  Tremendous heat within the Earth's crust produces the liquid magma. When the magma cools and hardens either underneath or on the Earth's surface, it produces igneous rocks. The rate at which a rock cools from a liquid state to a solid influences its shape and texture, characteristics that help to classify the rock as igneous. Granite is an igneous rock that cools below the earth's surface.  It is a hard rock with "speckles" of quartz crystals. Other igneous rocks cool above the surface of the earth and are known as volcanic rocks. Two examples of this, obsidian and pumice look very different from each other. The most rapid cooling of lava results in obsidian.

Metamorphic

Metamorphic implies a change of form or composition. Metamorphic rocks are formed deep within the earth when previously existing rocks undergo changes due to intense pressure, chemical reactions and heat. Often these rocks are former sedimentary rocks that have been recrystallized (a repetition of the rock forming process). E.g. slate is recrystallized shale, marble is recrystallized limestone and quartzite is recrystallized sandstone.

Sedimentary

Sedimentary rocks are made up of sediments or small pieces of rocks, shells, or the remains of plants and animals. Over millions of years these sediments have settled to the bottom of the oceans or lakes. When layers of sand and mud are pressurized together over time it produces sedimentary rocks. The most familiar type of sedimentary rock found  is sandstone. The layers in sedimentary rock are quite evident.  Shale is the most abundant sedimentary rock.  It is made from mud and clay deposits, is very soft and weathers rapidly.

Minerals

Minerals are either free, uncombined native elements or elemental compounds.  Our definition in this activity is simply that they are the substances that make up rocks. A mineral is a natural occurring inorganic solid (with the exception of water, mercury and opal) with a definite chemical composition (atomic structure) and crystalline structure. Each mineral's composition varies within fixed limits.