Rocks are made from one or more mineral. A mineral is a natural, usually inorganic solid with an orderly crystalline structure and a definite chemical composition.  A mineral is not man made. It is formed by natural geologic processes. Therefore manufactured and synthetic substances are not minerals. An inorganic substance is not made from a living thing. Coal is made from the buried remains of plants that lived millions of years ago in a swampy environment. Therefore coal is not a mineral. A mineral is made from a substance that was never alive such as table salt.

table salt image If you look closely at table salt, it looks like it consists of tiny, shiny crystals.  A crystal is a solid with a repetitive internal structure of atoms, ions, or molecules. They are geometrically arranged to form a pattern. The internal arrangement of atoms inside a mineral help form its particular shape.

Fluorite is also a type of mineral that has an orderly crystalline structure because its atoms or ions are arranged in a repetitive and orderly manner. It contains a unique combination of one calcium ion for every two fluoride ions. The one to two ratios of ions also gives fluorite its definite chemical composition and like most minerals, it is a compound.  Some minerals do consist of only one element.  They are called native elements.  Some examples of native elements are gold, silver, and copper.  Minerals can be classified into groups based on their specific characteristics, physical properties, and chemical nature.  The major mineral groups are silicates, carbonates, oxides, sulfides, sulfates, halides, and native elements.  Please watch the videos, How to Identify Minerals and Classifying Minerals, located in the sidebar. As you watch the videos, please take notes on how to identify and classify minerals.

You can also click on the Rocks for Kids link located in the sidebar to learn more about the characteristics used to study and identify minerals. One of the most useful properties used to identify a mineral is hardness. The Mohs Scale of Hardness consists of the known hardness of ten minerals. The minerals are arranged on the Mohs scale from 10 (the hardest) to 1 (softest). An unknown mineral’s hardness can be determined by its ability to scratch one of the minerals on the Mohs scale.   For example, a fingernail has a hardness of 2.5. Any mineral that has hardness less than 2.5 can be scratched by a fingernail.

Scientists have identified over 4,000 minerals in Earth’s crust.  Only about 30 of those minerals are responsible for forming Earth’s rocks.  A few of the most common rock forming minerals are quartz, feldspar, mica, calcite, and halite. They make up about 90% of the mass of Earth’s crust.  These minerals are made up of a combination of elements.  The most abundant elements in the Earth’s crust from greatest to least amount are oxygen, silicon, aluminum, and iron.

The majority of minerals form in shallow ocean waters. Minerals can also form deep within the crust or mantle where the temperatures are very hot. In both situations, the minerals are rearranged into crystalize structures.