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Igneous rock: Obsidian mahogany
What are minerals?
A mineral is a naturally occurring solid substance. Most minerals have an exact Crystal structure' target='_parent'>crystal structure and are found in rocks. Chemical elements are also classified among the minerals. Mineralogy is the science of minerals, their chemical composition and their Crystal structure' target='_parent'>crystal structure. Some useful minerals for humankind occur in such a large amount that it can be exploited as ore.
Minerals are usually composed of molecules which are a connection between multiple types of atoms. The molecules are arranged in a specific Crystal structure' target='_parent'>crystal structure. The Crystal structure' target='_parent'>crystal structure and the chemical composition of a mineral will ultimately determine the properties. The various types of minerals are distinguished by differences in their characteristics.
The igneous rocks on Earth are a mixture of various types of minerals. Certain rocks consist exclusively of crystals of minerals that have grown next to each other. Sedimentary rocks consist of reworked pieces (clasts) of original igneous rocks and usually also contain minerals. Sandstone consists largely of pieces of the mineral Quartz which originated from eroded igneous rocks. Also in sedimentary rocks minerals occur under the influence of various (chemical) processes.
Most rock types consist mainly of minerals of the Silicates group. These minerals contain silicon. Almost all igneous rocks, metamorphic rocks and some sedimentary rocks are included. An important exception is limestone which is composed of carbonates.
Types of minerals
The classification of minerals has been the subject of many discussions. We discuss here the classification of Strunz, commonly used in Europe, but there are many more classifications in use. Most classifications also have subcategories.
- 1 Elements (e.g. metals, Carbon and Sulfur)
- 2 Sulfides and Sulfosalts (e.g. Pyrite)
- 3 Halides (e.g. Halite, or salt)
- 4 Oxides (e.g. Cuprite)
- 5 Carbonates (e.g. Calcite and Dolomite)
- 6 Borates (e.g. Boracite)
- 7 Sulfates (e.g. Gypsum and Barite)
- 8 Phosphates, Arsenates and Vanadates (e.g. Turkois)
- 9 Silicates (e.g. Quartz, Feldspar, Biotite, Muscovite, Olivine, Pyroxenes and Amphibole)
- 10 Organic compounds (e.g. mellite and whewellite)
Minerals are very difficult to identify properly with only the color and the crystal shape. For a conclusive identification, it is needed to view thin sections of the mineral under a polarizing microscope. For further investigation, for example, also X-ray fluorescence spectrometry and electron microanalysis is applied.
The color of minerals is strongly influenced by the occurrence of various metals and elements present in the mineral. A small amount of "pollution" in the mineral can significantly affect the color. The color is therefore not a strong identification characteristic.
There are many kinds of minerals but most of them are very rare and are only found in specific locations. With basic knowledge of some common minerals, you can still get a good identification.
Do you have additional information for this article? Please contact the Fossiel.net Team.