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الموضوع: Minerals II Properties

  1. #1
    عضو مميز الصورة الرمزية مالك محمد
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    Aug 2011
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    افتراضي Minerals II Properties


    ©NASA
    Figure 1: The small spheres in this picture were dubbed "berries" by geologists who first saw them. They sit on the surface of Mars and were photographed by the Mars rover Opportunity. A mass spectrometer on the rover was able to determine the chemical content of the berries and geologists recognized the chemical formula for hematite (Fe2O3). Photograph courtesy of NASA.
    Geologists have recently determined that the بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى goethite and hematite exist in abundance on Mars, sure signs of the presence of water. None of those geologists have been to Mars, of course, but the unmanned rovers Spirit and Opportunity have. These rovers are equipped with three بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى , each of which is capable of determining the chemical composition of a solid with a high degree of بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى . With such a precise chemical analysis in hand, geologists on Earth had no problem identifying the minerals (see Research link to the right).
    A بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى is defined in part by a specific chemical composition. In بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى , therefore, it is always easy to identify a mineral, if you can determine the chemical composition with a بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى like the Mars rovers. In reality, however, even if you are looking at rocks on earth, determining the exact chemical composition of a substance involves significant time preparing the sample and sophisticated laboratory equipment (and often significant money). Luckily, it is usually unnecessary to go to such lengths, because there are much easier ways that require little more than a magnifying lens and a penknife. The most common minerals can be quickly identified in the field using basic physical properties such as color, shape, and hardness. The context of a mineral is important, too – specific minerals only grow under specific conditions, so context can often be used to rule out minerals that have similar color, for example. Although there are many thousands of named minerals, only a dozen or so are common in the earth’s بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى . Testing a few physical properties therefore بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى that you can identify about 90% of what you are likely to encounter in the field.
    Because the physical properties of a بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى are determined by its chemical composition and internal atomic structure, they can be used diagnostically, the way a runny nose and sore throat can be used to diagnose a cold. There are many physical properties of minerals that are testable with varying degrees of ease, including color, بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى form (or shape), hardness, luster (or shine), بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى , and cleavage or fracture (how the mineral breaks). In addition, many minerals have unique properties, such as بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى , fluorescence under black light, or reaction to بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى . In most cases, it is necessary to observe a few properties to identify a mineral; to extend the medical analogy even further, a runny nose is a symptom of a cold بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى , allergies, or a sinus infection among other things, so we have to use other symptoms to diagnose the problem – a headache, fever, watery eyes, and so on.
    Color

    The most obvious property of a mineral, its color, is unfortunately also the least diagnostic. In the same way that a headache is a symptom for a whole host of problems from the flu to a head injury, many minerals share the same color. For example, several minerals are green in color – olivine, epidote, and actinolite, just to name a few. On the other extreme, one mineral can take on several different colors if there are impurities in the chemical composition, such as quartz, which can be clear, smoky, pink, purple, or yellow.
    Part of the reason that the color of minerals is not uniquely diagnostic is that there are several components of the بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى compositions and structure that can produce color. The presence of some بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى , such as iron, always results in a colored mineral, but iron can produce a wide variety of colors depending on its state of oxidation – black, red, or green, most commonly. Some minerals have color-producing elements in their crystal structure, like olivine (Fe2SiO4), while others incorporate them as impurities, like quartz (SiO2). All of this variability makes it difficult to solely use color to identify a mineral. However, in combination with other properties such as crystal form, color can help narrow the possibilities. As an example, hornblende, biotite, and muscovite are all very commonly found in rocks such as بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى . Hornblende and biotite are both black, but they can be easily distinguished by their crystal form because biotite occurs in sheets, while hornblende forms stout prisms (see photos below). Muscovite and biotite both form in sheets, but they are different colors - muscovite is colorless, in fact.
    Figure 2: These three minerals can be distinguished using both color and form. Biotite and hornblende share the same color, but are different forms; muscovite and biotite share form but not color. Images courtesy National Park Service.
    Crystal form

    The external shape of a mineral crystal (or its crystal form) is determined largely by its internal atomic structure, which بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى that this property can be highly diagnostic. Specifically, the form of a بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى is defined by the angular relationships between crystal faces (recall Steno's Law of Interfacial Angles as discussed in بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى module). Some minerals, like halite (NaCl, or salt) and pyrite (FeS) have a cubic form (see below left), others like tourmaline (see below middle) are prismatic. Some بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى , like azurite and malachite, which are both copper ores, don't form regular crystals, and are amorphous (below right).
    ©Corel Corporation
    Figure 3: Examples of different types of crystal forms. On the left, pyrite has a cubic form; tourmaline (middle) is prismatic; azurite and malachite (on the right) are often amorphous.
    Unfortunately, we don’t always get to see the crystal form. We see perfect بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى only when they have had a chance to grow into a cavity, such as in a geode. When crystals grow in the context of a cooling بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى , however, they are competing for space with all of the other crystals that are trying to grow and they tend to fill in whatever space they can. The shape of the crystal can vary quite a bit depending on the amount of space available, but the angle between the crystal faces will always be the same.
    Hardness

    The hardness of a بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى can be tested in several ways. Most commonly, minerals are compared to an object of known hardness using a scratch test – if a nail, for example, can scratch a crystal, than the nail is harder than that mineral. In the 1820s, بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى , an Austrian mineralogist, developed a relative hardness scale based on the scratch test. He assigned integer numbers to each mineral, where 1 is the softest and 10 is the hardest. This scale is shown to the right.
    The scale is not بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى (corundum is actually 4 times as hard as quartz), and other methods have now provided more rigorous measurements of hardness. Despite the lack of بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى in the Mohs scale, it remains useful because it is simple, easy to remember, and easy to test. The steel of a pocketknife (a common tool for geologists to carry in the field) falls almost right in the middle, so it is easy to distinguish the upper half from the lower half. For example, quartz and calcite can look exactly the same – both are clear, colorless, translucent, and occur in a wide variety of rocks. But a simple scratch test can tell them apart; calcite will be scratched by a pocketknife or rock hammer and quartz will not. Gypsum can also look a lot like calcite, but is so soft that it can be scratched by a fingernail.
    Variations in hardness make بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى useful for different purposes. The softness of calcite makes it a popular material for sculpture (marble is made up entirely of calcite), whereas the hardness of diamond بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى that it is used as an abrasive to polish rock.
    Luster

    The luster of a بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى is the way that it reflects بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى . This may seem like a difficult distinction to make, but picture the difference between the way light reflects off a glass window and the way it reflects off of a shiny chrome car bumper. A mineral that reflects light the way glass does has a vitreous (or glassy) luster; a mineral that reflects light like chrome has a metallic luster. There are a variety of additional possibilities for luster, including pearly, waxy, and resinous (see pictures below). Minerals that are as brilliantly reflective as diamond have an adamantine luster. With a little practice, luster is as easily recognized as color and can be quite distinctive, particularly for minerals that occur in multiple colors like quartz.
    Figure 4: Examples of only a few of the different lusters that can be seen in minerals. Galena (on the left) has a metallic luster, amber (in the middle) is resinous, and quartz (on the right) is glassy.
    Density

    The بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى of بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى varies widely from about 1.01 g/cm3 to about 17.5 g/cm3. The density of water is 1 g/cm3, pure iron has a density of 7.6 g/cm3, pure gold, 17.65 g/cm3. Minerals, therefore, occupy the range of densities between water and pure gold. Measuring the density of a specific mineral requires time-consuming techniques, and most geologists have developed a more intuitive sense for what is “normal” density, what is unusually heavy for its size, and what is unusually light. By “hefting” a rock, experienced geologists can usually guess if there is an unusual amount of minerals that contain iron or lead, for example, because it feels heavier than an average rock of the same size (see our بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى module for more information).
    Cleavage and fracture

    Most بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى contain inherent weaknesses within their atomic structures, a plane along which the bond strength is lower than the surrounding bonds. When hit with a hammer or otherwise broken, a mineral will tend to break along that plane of pre-existing weakness. This type of breakage is called cleavage, and the quality of the cleavage varies with the strength of the bonds. Biotite, for example, has layers of extremely weak بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى that break very easily, thus biotite breaks along very flat planes and is considered to have perfect cleavage (see picture above). Other minerals cleave along planar surfaces of varying roughness – these are considered to have good to poor cleavage.
    ©Clay Hamilton
    Figure 5: Several conchoidal fractures are visible in this piece of quartz. Note the concave surface and the curved ribs.
    Some بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى don’t have any planes of weakness in their atomic structure. These minerals don’t have any cleavage, and instead they fracture. Quartz fractures in a distinctive fashion, called conchoidal, which produces a concave surface with a series of arcuate ribs similar to the way that glass fractures (see the picture to the right). For quartz, in fact, this lack of cleavage is a distinguishing property.
    Mineral بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى systems

    Physical properties provided the main basis for بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى of بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى from the بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى through the mid-1800’s. Minerals were grouped according to characteristics such as hardness, so that diamond and corundum would be in the same class of minerals. As the ability to determine the chemical composition of minerals developed, so did a new classification بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى . Many scientists contributed to the discovery of mineral chemical formulas, but بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى , a mineralogist at Yale University from 1850 to 1892 (see Biography link to the right), developed a classification system for minerals based on chemical composition that has survived to the present day. He grouped minerals according to their بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى , such as oxides (compounds with O2-), silicates (compounds with (SiO4)4-), and sulfates (compounds with (SO4)2-). A chemical classification system meant that minerals that were grouped together theoretically also tended to appear with each other in rocks since they tended to develop under similar chemical circumstances.
    Physical properties still provide the main بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى for identification of minerals, however, though they are no longer used to group minerals (from the example above, corundum is an oxide while diamond is a pure بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى , so by Dana’s بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى , they are in separate groups). A composition-based grouping highlights some common mineral associations that allow geologists to make educated guesses about which minerals are present in a rock, even with only a quick glance. By far, the most common minerals are the silicates, which make up 90% of the earth’s بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى . Of the many hundreds of named silicate minerals, only about eight are common, one of which is quartz. The uncommon minerals are critical, however, as they include economically important ones such as galena, which is the primary ore for lead, and apatite, a phosphate mined for phosphoric بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى that is added to fertilizers. The discovery of new ore deposits depends on the ability of geologists to identify what they see in the field and recognize unusual mineral occurrences that should be explored in more detail in the laboratory. A hand lens, a pocketknife, and a lot of practice still provide the easiest and cheapest methods of identifying minerals.

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  2. #2
    مشرفة الاقسام الاكاديمية الصورة الرمزية تمارا احمد
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    افتراضي رد: Minerals II Properties

    شكرا ...
    بارك الله فيك


    بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى

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  3. #3
    عضو ذهبي الصورة الرمزية زهراء غانم
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    افتراضي رد: Minerals II Properties

    Thank you
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    Super Moderator الصورة الرمزية منى زهران
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    افتراضي رد: Minerals II Properties

    بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى
    بعد التسجيل عليك الرد بكلمة شكرا وعمل refresh للصفحة لرؤية المحتوى في المشاركة الاولى

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  5. #5
    عضو ذهبي الصورة الرمزية sajeda zaben
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    افتراضي رد: Minerals II Properties

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    عضو مميز الصورة الرمزية عماد الكردي
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