Physical Geography - Version 1 Unit 8 Basic Mineral Development

Figure Halite Crystals . Image by Jeremy is used under a license . UNIT BASIC MINERAL DEVELOPMENT Goals Objectives of this unit Explain how minerals are formed and identified . Describe how color , luster , and streak are used to identify minerals . Identify additional properties that can be used to identify some minerals . GEOGRAPHY

MATERIALS OF EARTH CRUST The best way to learn about Earth crust would be to travel around the world , viewing minerals , rocks , and structures in a variety of places to see what they are and how they can be coaxed into telling Earth story . All matter is made of tiny particles . Protons , neutrons , and electrons form atoms that bond together to create molecules . Atoms are the smallest units that have the properties of the element they are , and molecules are the smallest units of a compound . For example , water is made of hydrogen and oxygen , but a molecule of water is very different from an atom of hydrogen or an atom of oxygen . The atoms combine to form molecules by different types of chemical bonding . Molecules bond into structures as well . The structures created by molecules form the different types of minerals , most importantly silicates , which are the substances that make up most of Earth crust . Other important minerals are and native elements , which are some of the most important materials used by society . Minerals come together to create the three major rock types , igneous , sedimentary , and metamorphic . These rocks are the material part of the rock cycle , which will be discussed in the following units ) Atoms to Molecules Everything you can see , touch , smell , feel , and taste is made of atoms . Atoms are the basic building block of all matter , so if we want to know about what Earth is made of , then we have to know a few things about these incredibly small objects . Everyday experience should convince you that matter is found in myriad forms , yet all the matter you have ever seen is made of atoms , or atoms stuck together in configurations of dizzying complexity . A chemical element is a substance that can not be made into a simpler form by ordinary chemical means . The smallest unit of a chemical element is an atom , and all atoms of a particular element are identical . There are two parts to an atom . At the center of an atom is a nucleus made up of two types of particles called protons and neutrons . Protons have a positive electrical charge . The number of protons in the nucleus determines What element the atom is . Neutrons are about the size of protons but have no charge . Electrons , much smaller than protons or neutrons , have a negative electrical charge , move at nearly the speed of light , and orbit the nucleus at exact distances , depending on their energy . GEOGRAPHY

Proton Nucleus Neutron Electron Figure The Anatomy ofan Atom . Image is used under a Alike . IONS Atoms are stable when they have a full outermost electron energy level . To fill its outermost shell , an atom will give , take , or share electrons . When an atom either gains or loses electrons , this creates an ion . Ions have either a positive or a negative electrical charge . What is the charge of an ion if the atom loses an electron ?

An atom with the same number of protons and electrons has no overall charge , so if an atom loses the negatively charged electron , it will have more protons , therefore , a positive charge . Ions with a positive charge are referred to as a cation ( pronounced ) What is the charge of an ion if the atom gains an electron ?

If the atom gains an electron , there will be more electrons and will have a negative charge . are ions that have a negative charge . MOLECULES When a cation gets close to an anion , they link up because oftheir different net charges , positive charges attract negative charges , and vice versa . When two or more atoms link up , they create a molecule . A molecule of water is made of two atoms of hydrogen ( and one atom of oxygen ( The molecular mass is the sum of the masses of all the atoms in the molecule . A collection of molecules is called a compound . BASIC MINERAL IDENTIFICATION Minerals can be identified by their physical characteristics . The physical properties of minerals are related to their chemical composition and bonding . Some characteristics , such as a GEOGRAPHY

hardness , are more useful for mineral identification . Color is readily observable and certainly obvious , but it is usually less reliable than other physical properties . Check out the mineral in Figure below . What is the color , shape ?

Are the individual crystals shiny or dull ?

Is there a definite crystalline structure ofthese minerals ?

In this unit , the properties used to identify minerals are described in more detail . Figure Fluorite Crystals . Image by Jeremy is used under a license . Color Color is the most feature of many minerals . Some minerals will always have a similar color , such as Gold , whereas some minerals , such as Quartz and Calcite , come in a variety of colors . The presence and intensity of certain elements will determine a specific color . Minerals with an inherent color ( all specimens of the mineral are the same color ) have essential elements in them which cause their color . Good examples are Azurite and Malachite , which has their strong blue and green color due to their copper in their atomic structure . But there are many minerals which have slight additions of elements in some specimens that cause it to be a different color . For example , pure Quartz ( is colorless , whereas Amethyst , a purple variety of quartz , has its purple color caused by traces of the element iron . The amount of iron present determines the intensity of the color . Certain minerals exhibit a color change when exposed to light , heat , radiation , or when atomic anomalies are present . Red Realgar transforms into yellow upon GEOGRAPHY

repeated exposure to light . Some minerals , such as Proustite and Vivianite , darken upon prolonged exposure to light , whereas other minerals , such as Kunzite fade . Some minerals undergo color changes when put under intense heat . This method is commonly used in the gemstone industry to artificially enhance the color of many gemstones . For example , some varieties of Topaz , Beryl , and Corundum are to produce deep colored gemstones from duller stones . Radioactivity can also have an effect , as is the cause of the color of Smoky Quartz . Figure Examples Mineral , Reacting Under Ultraviolet Light image on Commons by , Streak Streak is the color of a mineral powder . Streak is a more reliable property than color because streak does not vary . Minerals that are the same color may have a different colored streak . Many minerals , such as the rose quartz in the figure above , do not have , as they are harder than the plate . To check streak , scrape the mineral across an unglazed porcelain plate ( Figure below ) gold pyrite has a blackish streak , another indicator that pyrite is not gold , which has a golden yellow streak . The streak of hematite across an unglazed porcelain plate is . GEOGRAPHY

Figure Hematite Leaves a Streak an a Ceramic Plate Whether the Hematite has a Metallic Luster ar an Earthy Luster . Image by is licensed under a Alike International license . The streak test should be done on clean , weathered , or freshly broken specimens of the mineral . This is done to reduce the possibility that a contaminant , weathered coating , or tarnish will influence the results ofthe test . Select a representative point or protrusion on the specimen that will be scraped across the streak plate . With your other hand , place the streak plate flat on a tabletop or laboratory bench . Then , while holding the streak plate flat and firmly in place on the tabletop , place the point of the specimen firmly against the streak plate , and , while maintaining firm pressure , drag the specimen across the plate . Luster Luster describes the reflection of light off a surface . have special terms to describe luster . One simple way to classify luster is based on whether the mineral is metallic or . Minerals that are opaque and shiny , such as pyrite , have a metallic luster . Minerals such as quartz have a luster . Figure Examples ( a ) Diamond Has an Adamantine Luster . Quartz is Not Sparkly has a Luster . Sulfur Reflects Less Light , 50 it has a Luster . Image is used under a BY Attribution license . GEOGRAPHY

Hardness The ' scale of mineral hardness is named after Friedrich , a mineralogist who invented a scale of hardness based on the ability of one mineral to scratch another . Rocks are made up of one or more minerals . According to the scale , Talc is the softest it can be scratched by all other materials . Gypsum is harder as it can scratch talc but not calcite , which is even harder . The hardness of a mineral is mainly controlled by the strength of the bonding between the atoms and partly by the size of the atoms . It is a measure of the resistance of the mineral to scratching , the scale is for natural minerals . Figure Hardness Scale . Image is in the public domain . Diamond is always at the top of the scale , being the hardest mineral . There are ten minerals in scale , talc , gypsum , calcite , fluorite , apatite , feldspar , quartz , topaz , corundum , and for last and hardest , diamond . Because the scale was made long ago , it is not exactly correct , for example , several minerals are now known to be harder than the diamond . The scale may not be perfect , but field geologists still find it very useful . CLEAVAGE FRACTURE Cleavage refers to the way some minerals break along certain lines of weakness in their structure . Mica is a good example as it breaks along very closely spaced flat planes that yield GEOGRAPHY

thin sheets . Calcite is another good example , breaking along three different planes that yield blocky fragments that look like a rectangular box that has been warped , called a rhombohedron , simply , rhomb . Galena breaks along three planes at right angles to one another , producing true cubes as fragments . One cleavage direction Two cleavage directions Two cleavage directions at 90 degrees not at 90 degrees Three cleavage directions Three cleavage directions at 90 degrees not at 90 degrees Figure Examples of Mineral Cleavage . Image is used under a Creative Commons Alike license . are described in terms of their quality and how smoothly the mineral breaks , their resistance to fracture , and resulting shape . The quality of is perfect , imperfect , distinct , good , fair , and poor . The difficulty is described as easy , hard , and difficult to produce . By way of examples , the have perfect cleavage in one direction that is easy to produce calcite has a perfect cleavage in three directions that is also easy to produce the have perfect cleavage in one direction that is easy to produce and a good cleavage in another direction that is hard to produce and diamond has a perfect cleavage in four directions that is easy to produce . Sphalerite has perfect in six directions , some of which are easy to produce , others hard , hence you wo always see all six cleavage surfaces in any given sample of the material . GEOGRAPHY

Cleavage is the tendency of a mineral to break along certain planes to make smooth surfaces . Halite breaks between layers of sodium and chlorine to form cubes with smooth surfaces Figure Mica Exhibits of . Image is used under a BY Attribution license . Fracture is a break in a mineral that is not along a cleavage plane . Fracture is not always the same in the same mineral because fracture is not determined by the structure of the mineral . Minerals may have characteristic fractures . Metals usually fracture into jagged edges . If the mineral splinters like wood , it may be fibrous . Some minerals , such as quartz , form smooth curved surfaces when they fracture . Figure Chrysotile , Exhibits a Splintery Fracture . Image is used under a BY Attribution license . GEOGRAPHY

An atom has negatively charged electrons in orbit around its nucleus , which is composed of protons and neutrons , which have no charge . An atom that gains or loses electrons is an ion . Positively charged ions are , negatively charged ions are . Minerals can be identified by their physical characteristics . The physical properties of minerals are related to their chemical composition and bonding . Some characteristics , such as a mineral hardness , are more useful for mineral identification . Color is readily observable and certainly obvious , but it is usually less reliable than other physical properties . The International Mineralogical Association has established the following requirements for a substance to be considered a distinct mineral It must be a naturally occurring substance formed by natural geological processes , on Earth or other extraterrestrial bodies . This excludes compounds directly and exclusively generated by human activities ( anthropogenic ) or in living beings ( biogenic ) such as tungsten carbide , urinary calculi , calcium oxalate crystals in plant tissues , and seashells . It must be a solid substance in its natural occurrence . It must have a crystallographic structure or , more generally , an ordered atomic arrangement . It must have a fairly chemical composition . However , certain crystalline substances with a fixed structure but variable composition may be considered single mineral species . GEOGRAPHY