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Mineral

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Collage of minerals and what can be created using minerals

Minerals are inorganic compounds that naturally occur in the earth who have a qualifiable chemical composition and crystalline structure. Its name refers to its chemical composition and physical structure. Rocks are not the same as minerals and should not be confused with this term. A rock contains one or more minerals, and can also have organic materials [1].

Contents

Mineral definition and classification

Calcite and Quartz Sphere

A mineral can be an element or a chemical compound that normally is crystalline and is formed through geological processes. Biogenic materials have been excluded from the mineral kingdom because of mineral definition and classification scheme [1]

There are over 3,000 different kinds of minerals, so mineralogists have to group them all. Minerals are grouped into families based on their their chemical composition[1]. Many minerals with similar characteristics and can classified together. Mineralogist take in consideration streak, luster, sheen, hardness, cleavage, crystal system/habit, color, specific gravity,and clarity when they identify minerals[2]. There are many different grouping systems, but the most commonly used is the Dana system, which was devised by Professor James Dana in 1848 [1]Author Unknown.This system is divided into eight classes. They are: Native Elements, Silicates, Oxides, Sulfides Sulfates, Halides,Carbonates, Phosphates,and Mineraloid[2].

Chemical Properties of Minerals

Atoms, Molecules, and Elements

Everything on our planet is made up of many small building blocks called atoms. Each atom comes in various forms and each one of those are classified as elements. On earth there are ninety two elements that form naturally and the matter on the earth is made of twenty of these elements. Atoms can bond together because they can have positive and negative charges, which attracts them to each other. When atoms bond together they form molecules, from which mixtures and compounds are formed. A distinct ratio of particular molecules are in a mineral's structure. A mineral can have impurities when foreign molecules that are not part of its makeup are found. These impurities can change the mineral's appearance, like changing its color [3].

Chemical Formula

All minerals have elements in their structure and they are in an exclusive arrangement. The order of atoms will say what type of mineral it is. Al the different minerals have their own chemical formula. A chemical formula is made up of the types and amounts of the elements that are in a specific mineral. Elements have one or two letters to abbreviate their name. For example: the mineral Hematite's chemical formula is Fe2O3. The letters say what element is present and in this case "Fe" stands iron and "O" stands for oxygen. The sub-scripted numbers tell how many of those atoms are in each molecule, so there are 2 iron, and 3 oxygen, atoms. In some cases there are no numbers sub-scripted after the element and this means that there is only one atoms of that element [3].

The Dana System

  • Native Elements- A lot of minerals are made of combinations of chemical elements. This class is made up of the most pure minerals.
  • Silicates- This class has the largest group of minerals. Silicates are a combination of metals, silicon, and oxygen.
  • Oxides- oxides are minerals that are made from a combination of metal and oxygen.
  • Sulfides- sulfides are a kind of minerals that are made from compounds of sulfur(usually with metal). Most are heavy and brittle.
  • Sulfates- minerals which are made from a combination of compounds of sulfur, metal, and oxygen.
  • Halides- They are soft and can be easily dissolved in water and made from halogen elements that are combined with metallic elements.
  • Carbonates- minerals which are made of carbon, oxygen, and some metallic element.
  • Phosphates- The minerals in this class occur less than any other mineral family because they are formed after the breaking down of other minerals caused by weathering .
  • Mineraloid-These minerals are places into this class because they do not fit into any other eight classes[2].

Properties of Minerals

  • COLOR-Minerals have a unique color that can help to identify them. The color is usually more consistent when the mineral is opaque, so knowing the color that relates to the mineral is helpful when it comes to identification. The color in clear minerals usually varies. Color alone is not a reliable away to identify minerals [2].
  • STREAK- Streak is the name given to the mineral when it is in a powdered form, which shows the actual color of the mineral. As a solid, trace minerals can change color because of the light it can be reflecting. Trace minerals do not really change the color of the mineral when it is a powdered form. Metallic minerals usually have a streak that looks dark because of the light that is being absorbed by the small fragments of the streak. Non-metallic particles reflect most of the light so they look like they have a lighter color or are white. Streak is more accurate in determining the real color of the minerals so it is a more reliable way to identify minerals [2].
  • HARDNESS-Hardness is one of the best ways to identify a mineral. It is the measure of the mineral’s resistance to scratching. There are ten minerals whose hardness is already know and they form a scale called Mohs scale. The softest mineral known is called talc and its Mohs scale rating is one. Diamond is the hardest mineral with a Mohs scale of ten. Soft minerals can be easily scratched by harder minerals because the crystals have a weaker force holding them together and are broken by the harder mineral.[2].
Mohs Scale
1 Talc
2 Gypsum
3 Calcite
4 Fluorite
5 Apatite
6 Orthoclase Feldspar
7 Quartz
8 Topaz
9 Corundum
10 Diamond [2].
  • CLEAVAGE AND FRACTURE-Minerals usually break along lines or on their smooth surfaces when they are hit sharply. All minerals break in different ways and they show different types of cleavage. Cleavage brakes into two points. First, the mineral needs to be tested to see how easy cleavage is obtained. If the cleavage is obtained easily and the cleavage planes are easily notable then it is considered perfect. The cleavage is considered good if it is made with little difficulty but also has notable cleavage planes. Finally, a cleavage is considered imperfect if it was difficult to obtain and the planes are not easy to make out.Fracture shows the worth of the cleavage surface. A lot of minerals exhibit either an uneven or rough fracture, conchoidal fracture, or hackly fracture [2].
  • CRYSTALLINE STRUCTURE-Mineral crystals come in various shapes and sizes. Each individual shape is determined by the collection of atoms, molecules or ions that form the crystal and how they are connected to each other. There are fibers in the crystal that are almost impossible to see with the naked eye. Microcrystalline and cryptocrystalline structures are only visible with high magnification. If the crystal has no crystalline structure then it is called amorphous. There are not many amorphous crystals, these can only be see under extremely high magnification [2].
  • TRANSPARENCY OR DIAPHANEITY-Diaphaneity is the degree of transparency in a mineral, which depends on the thickness of the mineral [2].
  • TENACITY-How particles of a mineral hold together [2].
  • MAGNETISM-There are many different kinds of magnetism that allows a mineral to attract or repel other magnetic materials [2].
  • LUSTER-A property that mineral has that indicated the amount of light that is reflected off its surface. The luster can be affected by how bright the light is. It can be described in two different ways: metallic, submetallic, and nonmetallic. Metallic minerals are opaque and reflect light. Submetallic minerals are opaque and dull, which means they do not reflect a lot of light Nonmetallic minerals do not reflect any light.[2].
  • ODOR- Minerals do not have an odor unless they have been moistened, heated, breathed upon, or rubbed [2].
  • TASTE-Minerals that can be dissolved have taste[2].
  • SPECIFIC GRAVITY-Specific Gravity can be obtained by comparing the weight of the mineral and the weight of an equal amount of water. This can help identify minerals in the field [2].

The Difference between Rocks and Minerals

Minerals are inorganic solids that occur naturally. They have unique chemical makeup and crystal structure. Some may be made up of one kind of element, like diamonds are made of carbon, or they can have more elements [4].

Rocks on the other hand are made up of one or more minerals. Even though minerals compose a rock that does not make it a mineral. The minerals in a rock are tightly bonded together and make a hard solid. The classification of rocks depends on the process of its formation. Some rocks can also have organic matter and mineraloids in them [5]. Rock are classified into three families: igneous, sedimentary, and metamorphic rocks [4]. Rocks can be mined to get minerals from them, these rocks are called ores[5].

Gallery

References

  1. 1.0 1.1 1.2 1.3 Unknown Author. Mineral definition and classification Mineral Crusher. Web. Date of access: 30 January 2012.
  2. 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 2.15 Author Unknown.Mineral Classification Rocksandminerals. Web. Date of access: 30 January 2012.
  3. 3.0 3.1 Author Unknown.THE CHEMICAL PROPERTIES OF MINERALS minerals.net. Web. Access Date: March 28, 2012.
  4. 4.0 4.1 Unknown Author. Rocks and Minerals ontariogeoscience.net. Web. Date of access: 28 March 2012.
  5. 5.0 5.1 Author Unknown. Difference Between Rocks and Minerals differencebetween.net. Web. Access Date: 28 March 2012.
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