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picture1_Geology Pdf 200871 | Mines Outreach Education Features Rocks


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File: Geology Pdf 200871 | Mines Outreach Education Features Rocks
rocks minerals adapted from geology and geological features a photographic slide collection compiled by b f kean 1993 minerals are naturally formed crystals that are composed of one or more ...

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                                                                                                                                                                                          Rocks & Minerals
                                                      (Adapted from: Geology and Geological Features: A Photographic Slide Collection compiled by B.F. Kean,
                                                      1993)
                                                      Minerals are naturally formed crystals that are composed of one or more chemical elements. They are
                                                      distinguished from other natural solid materials by their crystalline structure. Some natural solid materials
                                                      formed in rocks are not minerals because they lack a crystalline structure, i.e., they are amorphous, eg.,
                                                      obsidian or volcanic glass. Most minerals are formed by inorganic processes; however, a few are formed
                                                      by organic processes (living organisms), eg., calcite in coral. 
                                                      Single-element minerals include diamond (from carbon) and the native (i.e., elemental) metals gold,
                                                      copper and silver. Other minerals, such as chalcopyrite, sphalerite and mica, are chemical compounds
                                                      consisting of several elements. 
                                                      Rocks are made up of minerals, the exception being glassy rocks (eg., some rhyolites). Most rocks are
                                                      polymineralic (i.e., contain more than one mineral); however, a few are monomineralic, eg., limestone and
                                                      marble. 
                                                      Rock-forming processes, some rapid and others requiring millions of years, are as active today as in the
                                                      geological past. Rocks are divided into three main classes: 
                                                      IGNEOUS ROCKS are formed as magma (molten rock) cools and solidifies. Magma is produced far
                                                      below the Earth's surface by heat generated mainly from radioactive disintegration of uranium, thorium
                                                      and potassium. The two main types of igneous rock are extrusive and intrusive. Extrusive rocks, or lava,
                                                      form when magmas reach the surface of the Earth through volcanic fissures or vents. They cool rapidly
                                                      and are fine-grained or glassy, eg., basalt and obsidian. Explosive eruptions produce rocks composed of
                                                      rock dust or fragments (pyroclasts). Intrusive rocks form when magma cools slowly at depth, eg., granite,
                                                      allowing the constituent minerals to grow much larger. These magmas intrude fissures and other zones of
                                                      weakness in the Earth's crust, crystallize, and are eventually uplifted and exposed by erosion. Some
                                                      magmas carry fragments of rocks and minerals from deep within the Earth, and this allows us to study
                                                      samples from regions too deep to be reached by drilling. The table below shows the relationship between
                                                      different igneous rocks and how they form.
                                                                                 Extrusive Igneous
                                                                                                                                                                                          Basalt                                                                   Andesite                                                                     Rhyolite
                                                                                 Rocks (volcanic)
                                                                                                                                                                                                                                                                                                                                    Granite batholith
                                                                                                                                                                               Gabbro stock;                                                               Diorite stock; 
                                                                                                                                                                                                                                                                                                                                                or stock;
                                                                                 Intrusive Igneous
                                                                                                                                                                                diabase dyke                                                                         or dyke
                                                                                                                                                                                                                                                                                                                                      pegmatite  dyke
                                                                                 Rocks
                                                                                                                                                                                                                                                                                                                                                   Quartz
                                                                                                                                                                                       Feldspar                                                                     Feldspar
                                                                                 Main
                                                                                                                                                                                                                                                                                                                                                 feldspar
                                                                                                                                                                                     pyroxene                                                                     pyroxene
                                                                                 Minerals
                                                                                                                                                                                                                                                                                                                                                     mica
                                                                                                                                                                                         olivine                                                                      olivine
                                                                                                                                                                                                                                                                                                                                                  olivine
                                                                                                                                                                                                                                                       MAGMA
                                                                                                                                                                                                                                                                    SSiOiO          (l(ligighht t ccoololouurreedd))
                                                                                                                                                                                                                                                                          22
                                                                                                                                                                                                  (d(daarkrk c coololouurreedd) )                 MMggOO
        SEDIMENTARY ROCKS are formed by the accumulation and cementing of loose sediment (eg.,
        sandstone), the deposition of chemical compounds held in solution in water (eg., limestone), or by the
        accumulation of animal or plant debris (eg., coal). 
        Wind, river and ocean currents are the main methods of transport. This transported material settles to
        form distinct layers, which are compressed by overlying layers and cemented to form solid rock. Rock
        layers can be distinguished from each other by differences in grain size, colour and composition. 
        Sedimentary rocks may have a coarse-grained, gravel-like appearance or be extremely fine grained, and
        may be hard or soft. The principal varieties are sandstone, limestone and shale. Many sedimentary rocks
        contain fossils and some, such as coral reefs, are composed entirely of such organic remains. The table
        below illustrates how sedimentary rocks form.
             1. Surface rock          Conglomerate
                               erosion
                                      Sandstone
                                      Shale
                                   precipitation
             2. Chemicals dissolved in sea water
                                      Limestone, Dolostone
                           accumulation
             3. Animal (shell, coral) or plant remains
                                          Coal seams
                               evaporation
             4. Salts dissolved in sea water
                                      Salt, Potash, Gypsum
                                                  METAMORPHIC ROCKS are formed when rocks of any class are subjected to heat and pressure at
                                                  depth. This causes new minerals to form and other minerals to recrystallize. During the process, material
                                                  from the rock may be added or lost. Marked changes in temperature (T) and pressure (P) occur, which
                                                  may produce completely new types of rocks. In addition to the formation of new minerals, existing
                                                  minerals may be realigned into parallel bands and new textures may be formed. At sufficiently high
                                                  temperatures, the rock may undergo partial melting to form magma, which may then become the source
                                                  of an igneous rock. Metamorphic rocks include, gneiss, schist, slate, quartzite and marble, and the table
                                                  below shows how they form.
                                                                              Sandstone
                                                                                                                          Shale                             Limestone
                                                                                                                                                                                                                                              Igneous, sedimentary or
                                                                                                                                                                                                                                             other metamorphic rocks
                                                                                       TT,P,P                                 TT,P,P                                     TT,P,P                               hhigighh T T, , PP                                  hhigighh T T, , PP                                   hhigighh T T, , PP
                                                                                                                                                                                                       flflaakkyy c cleleaavvaaggee                       ppaartrtiaial l mmeeltltiningg,,                   eexxtetennsisivvee m meeltltiningg
                                                                                                                                                                                                                                                           mminineeraral l bbaannddss
                                                                               Quartzite                                  Slate                                 Marble                                              Schist                                            Gneiss                                             Migmatite
                                                        The Geological Cycle
                 Sooner or later most rocks are exposed to the processes of erosion. The resulting products accumulate to
                 form sedimentary rocks. These may be buried to great depths and converted by heat and pressure into
                 metamorphic rocks. At still greater depths, they may be melted to form magma, which if crystallized forms
                 igneous rocks; if uplifted and exposed, these renew the cycle. The cycle may, however, be interrupted and
                 follow any of the paths shown in the diagram below.
                                                                             M
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...Rocks minerals adapted from geology and geological features a photographic slide collection compiled by b f kean are naturally formed crystals that composed of one or more chemical elements they distinguished other natural solid materials their crystalline structure some in not because lack i e amorphous eg obsidian volcanic glass most inorganic processes however few organic living organisms calcite coral single element include diamond carbon the native elemental metals gold copper silver such as chalcopyrite sphalerite mica compounds consisting several made up exception being glassy rhyolites polymineralic contain than mineral monomineralic limestone marble rock forming rapid others requiring millions years active today past divided into three main classes igneous magma molten cools solidifies is produced far below earth s surface heat generated mainly radioactive disintegration uranium thorium potassium two types extrusive intrusive lava form when magmas reach through fissures vents ...

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