# Science: An Elementary Teacher’s Guide/Types of Minerals
## Minerals

A mineral is a naturally occurring substance, representable by a chemical formula, that is usually solid and inorganic, and has a crystal structure. It is different from a rock, which can be an aggregate of minerals or non-minerals and does not have a specific chemical composition. The exact definition of a mineral is under debate, especially with respect to the requirement a valid species be abiogenic, and to a lesser extent with regard to it having an ordered atomic study of minerals is called mineralogy.
The silicate minerals compose over 90% of the Earth's crust. The diversity and abundance of mineral species is controlled by the Earth's chemistry. Silicon and oxygen constitute approximately 75% of the Earth's crust, which translates directly into the predominance of silicate minerals. Minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish various species, and these properties in turn are influenced by the mineral's geological environment of formation. Changes in the temperature, pressure, or bulk composition of a rock mass cause changes in its minerals.
Minerals can be described by various physical properties which relate to their chemical structure and composition. Common distinguishing characteristics include crystal structure and habit, hardness, lustre, diaphaneity, colour, streak, tenacity, cleavage, fracture, parting, and specific gravity. More specific tests for minerals include magnetism, taste or smell, radioactivity and reaction to acid.
The Rocks of the crust can me divided into three groups.
Sedimentary rock, they are made of layers of sediment that gather together on the earth's surface and are pressed together by pressure and chemicals. Igneous rock, forms of molten rock material, which is called magma. These two types of rocks are exposed to really high temperatures and pressures. Metamorphic rock, is a rock that has under gone a change.
Minerals are defined as solid, inorganic naturally compounds. Almost of all chemical elements of the earth, crust is associated with one mineral. Minerals grow in a wide variety of geological environments for example Deep Ocean, salt lakes, and volcanoes.

## Types of Minerals

Minerals do not come from living things. Geologists classify minerals into four major categories, depending on the chemicals in them and the structure of the crystals they form.
1. Silicate Minerals first category are those that contain the chemical element silicon. Common examples of this group include quartz, feldspar, mica, garnet, hornblende, augite, and talc. About 40% of the commonly known minerals are of this group, including the minerals found in granite.
2. Nonmetallic Minerals second category, although some of them contain metals, such as calcium or magnesium. This group includes such well-known minerals as sulfur, rock salt, gypsum, calcite, dolomite, fluorite, graphite, and apatite.
3. Metallic Minerals third category of metal ore minerals. These include gold, silver, copper, iron, lead, zinc, aluminum, tin, mercury, uranium, and titanium.
4. Gem Minerals fourth category are the gem minerals, which are those that are made into precious and semiprecious stones. These include diamonds, emerald, ruby, opal topaz, jade, sapphire, and others.

## Identifying Minerals

Each mineral has its own unique characteristics. A variety test are usually performed on minerals in order to correctly identify them:
Color Test which is the color of a freshly cleaned surface.
Streak Test (the color of a minerals powder) mineral is scratched on an unglazed porcelain white tile.
Hardness Test (resistance to be scratched; is very useful since a mineral's hardness is constant)certain minerals are used as standards, then the unknown mineral is used to try to scratch the known standards. To determine the hardness of a mineral you must try to scratch the mineral against a glass plate. Hardness is measured on a scale from 1 being the lowest to 10 being the highest. Basically how hard is it to scratch the mineral i.e. diamonds are hard to scratch.
Other Tests
* Luster (the way a mineral shines in reflected light)is it dull, silky, pearly, glassy
* Crystal form is it square, cubical, pyramid shaped
* Magnetic is the ability to attract magnet
* Odor sometimes the powder of a mineral has a certain odor i.e. sulfur smells like rotten eggs
A mineral is:
* Naturally occurring
* Definite chemical composition
* Inorganic solid
* Crystalline structure
* Definite set of chemical and physical properties

## External Links

8th Grade Science Class Mineral Identification Video