Minerals
a naturally occurring solid formed through geological processes that has acharacteristic chemical composition, a highly ordered atomic structure, and specific physical properties. A rock, by comparison, is an aggregate of minerals and/or mineraloids and need not have a specific chemical composition. Minerals range in composition from pure elements and simple salts to very complex silicates with thousands of known form. The study of minerals is called mineralogy
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Characteristics of a Mineral
The Mohs Scale of Hardness is used to explain how hard a mineral is. Hardness ranges from 1 [soft] to 10 [hard]. Since a mineral can only be scratched by something that is harder than it is, its place on the Mohs Scale is usually explained with a description of the thing that will scratch it. A mineral that is higher in number on the scale, will scratch anything that has a lower number. For example, Topaz that is an 8 on the scale will scratch Talc that is a 1. On the other hand, Topaz won't scratch a diamond that is a number 10. Gemstones are always harder minerals. Even though there are other pretty minerals, they are not used as gemstones unless they are hard. Gemstones cost a lot of money and if they were soft, they would break easier. The gemstones couldn't be used for jewelry if they were soft. On the chart below, the gemstones are higher numbers since they are harder
external image Hardness%20scale.gif The hardness scale is not a normal scale with even changes from one number to another. It looks more like the diagram to the right. You can see that the numbers from one to seven are evenly spaced apart. This means that it is a gradual rise in hardness from one to two, from three to four, and so on. But when you get to the hardest part of the scale, the hardness increases a lot. This means that there is a big difference in the hardness of a diamond, for example, that is a 10 on the scale and a mineral that is nine. If you didn't see a diagram like the one on the right, you wouldn't know that there were such big differences between the numbers.
Mineralogists know what colors the minerals usually are. An example of this is the diamond. After studying diamonds for years and years, scientists can say, from experience, that diamonds are usually colorless, yellow, or grey. They also know that they can be other colors, too. Color is only one of the characteristics that they use to identify a mineral. Because there are differences in minerals [like colors], mineralogists don’t depend on just one of the characteristics to figure out which mineral it is. They use them all.
This is the color of the dust that is left after you grind up a mineral. In school, we usually use something called a streak plate because we can’t just pound all the minerals into dust to test streak. Instead, we rub the mineral on the ceramic plate which has a hardness of 7. Any mineral that is softer than 7 will leave a little dust on the plate when it is rubbed on it. The color of the dust is a mineral characteristic. Sometimes the color of the dust is different than the color of the mineral.
Cleavage is how a mineral splits. Some minerals split evenly in one direction into sheets, like Mica . Other minerals always split in three or four directions. The mineral does the same split every time. If you had 2000 chunks of Mica, every one would split in one direction into thin sheets. Because it happens every time, it is a way to identify a mineral.
When a mineral shatters, it doesn’t always break evenly like cleavage. It fractures into different shapes depending on what mineral it is. Some have jagged edges, some have smooth ones, and some break into grains or uneven chunks. Mineralogists expect certain minerals to fracture into jagged pieces because they always do.
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Mineralogists will check to see if the mineral is magnetic or not. If it is attracted to a magnet, it is magnetic. If it is not attracted to a magnet, it isn't magnetic. This is another way to identify a mineral.
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This is the weight of the mineral compared to the weight of water. This tells the scientist how heavy a mineral is. For example: platinum is very, very heavy. Mineralogists are able to narrow down what the mineral is based on its weight. Metals are heavier than regular minerals.
there are lots of different crystal formations. A mineral always has the same one. With each mineral, we named the crystal system with its proper name and then our team artist drew a picture of what the crystal looks like. We felt this would be easier to understand than axes, prisms, and symmetry.
Most minerals are transparent, translucent, or opaque. Transparent means that light can shine straight through it. An easier description is that you can see right through it like you do with window glass. Translucent means that light can shine through it but its path is changed when it exits. An easier description is that it is blurry to look through. Opaque means that light won't go through it at all. Our easier description is that you can't see through it at all.
Chemical Properties of a Mineral
Minerals may be classified according to chemical composition. They are here categorized by aniom group. The list below is in approximate order of their abundance in the Earth's crust. The list follows the Dana classification system, which closely parallels the Strunz classification Silicate class
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The largest group of minerals by far are the silicates (most rocks are ≥95% silicates), which are composed largely of silicon and oxygen with the addition of ions such as aluminum ,magnesium, iron, and calcium . Some important rock-forming silicates include the feldspars, quarts,olivines ,pyroxenes,amphiboles , garnets, and micas.
Carbonate class
The carbonate minerals consist of those minerals containing the anion (CO3)2- and include calcite and aragonite (both calcium carbonate), dolmite (magnesium/calcium carbonate) and siderite (iron carbonate). Carbonates are commonly deposited in marine settings when the shells of dead planktonic life settle and accumulate on the sea floor. Carbonates are also found in evaporitic settings (e.g. the Great Salt Lake Utah ) and also in Karst regions, where the dissolution and reprecipitation of carbonates leads to the formation of caves stalactites and atalgmites. The carbonate class also includes the nitrate and borate minerals.
Sulfate class
Sulfate Minerals all contain the sulfate anion, SO42-. Sulfates commonly form in evaporitic settings where highly saline waters slowly evaporate, allowing the formation of both sulfates and halides at the water-sediment interface. Sulfates also occur in hydrothermal vein systems as gangue minerals along with sulfide ore minerals. Another occurrence is as secondary oxidation products of original sulfide minerals. Common sulfates include anhydrite (calcium sulfate), celestine (strontium sulfate), barite (barium sulfate), and gypdum (hydrated calcium sulfate). The sulfate class also includes the chromate , molybdate, selenate , sulfite ,tellurate , and tungstate minerals.
Halide class
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The halide minerals are the group of minerals forming the natural salts and include fluorite (calcium fluoride), halite (sodium chloride), sylvite (potassium chloride), and sal ammoniac (ammonium chloride). Halides, like sulfates, are commonly found in evaporite settings such as playa lakes and landlocked seas such as the Dead Sea and Great Salt Lake. The halide class includes the fluroride, choride, bromide, iodide minerals.







Properties of Minerals Some minerals are not really in a family because they are composed of only one element. There are only twenty elements that are found in a native, solid state that we can classify as minerals. Some of these elements are considered metallic including gold, silver, copper, lead, platinum, palladium, iridium, osmium, iron, nick, mercury, tantalum, tin, and zinc. There are also nonmetallic native minerals including sulfur and carbon in the form of graphite and diamond. Three native minerals are considered semimetals which include arsenic, antimony, and bismuth.
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Diamond
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elements occur naturally on earth. Most are very rare. About 20 elements make up over 95 percent of material on the earth (including the earth itself). Each mineral has a unique arrangement and the number of elements contained in its Crystal Structure
Physical Properties of Minerals-Classifying minerals can range from simple to very difficult. A mineral can be identified by several physical properties, some of them being sufficient for full identification without equivocation. In other cases, minerals can only be classified by more complex chemical.
Special properties- A mineral's color is generally the result of trace elements within the mineral. Textures describes how minerals feel, and luster describes how a mineral reflects light. Cleavage and fracture describe how minerals break.
CHARACTERISTICS OF MINERALS (DO NOT DELETE)
Streak...
When a mineral is rubbed firmly across a streak plate, it leaves a mark, or a streak, of powder. When describing a mineral's streak, you simply state the color of the streak. For example, if you were streak testing the mineral quartz, you would find that it leaves a white streak. In your description you would write, "This mineral leaves a white streak." It's as simple as that!
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Cleavage or Fracture...

In our first lab identifying minerals, we talked about cleavage and fracture as being "how the mineral breaks apart." So, a simple definition of this property is simply, Cleavage and Fracture describe how a mineral breaks apart. More technically speaking,cleavage and fracture are two separate ways to describe how a mineral breaks apart. For example, a mineral is said to have cleavage if when it breaks it forms a flat surface. A mineral is said to have fracture if when it breaks it forms a non-flat surface. Just remember that cleavage and fracture both describe how a mineral breaks apart. Cleavage is the tendency of a mineral to break along smooth planes parallel to zones of weak bonding. Hardness... Hardness simply describes how hard a mineral is. This can be tested by scratching the mineral. Check this out... A mineral can only be scratched by something that's harder than it. A hard mineral can scratch a soft mineral, but a soft mineral cannot scratch a harder mineral. So, We can actually test hardness by simply seeing which minerals scratches another.



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