Download Structure of Minerals Structure of minerals

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Structure of Minerals
Structure of minerals
} An orderly array of atoms chemically bonded to form a
particular crystalline structure
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Structure of minerals
} An orderly array of atoms chemically bonded to form a
particular crystalline structure
} Arrangement primarily determined by the sizes of ions
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Relative Sizes of Common Elements
Ideal Geometric Packing
for Various-sized Ions
Ideal Geometric Packing
for Various-sized Ions
} Each cation surrounded by the largest number of anions that will fit.
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The Orderly Arrangement of Sodium and Chloride Ions Is
Reflected in the Cubic Shape of the Halite Crystal
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Def: Polymorphs
} Different minerals with the same chemical composition but different
crystalline structures
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Def: Polymorphs
Graphite, diamond, and buckminsterfullerene are all made of Carbon!
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Diamond and graphite: polymorphs of C
Classification of Minerals
} Nearly 4000 minerals have been identified on Earth!
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Classification of Minerals
} Nearly 4000 minerals have been identified on Earth!
} Rock-forming minerals
ÑMake up most of Earth’
Earth’s crust
ÑOnly a few dozen
ÑComposed mainly of the 8 common elements
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Silicon-oxygen tetrahedron – the silicate building block
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How do the silicon-oxygen tetrahedra balance their
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charges?
}By bonding with positive ions
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How do the silicon-oxygen tetrahedra balance their
charges?
}By bonding with positive ions
}By sharing their oxygen ions to form structures
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Classification of Minerals
} Silicate structures
ß Isolated tetrahedra
ß Single chain structures
ß Double chain structures
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Classification of Minerals
} Silicate structures, cont.
ß Sheet or layered structure
ß Complex 3-dimensional structures
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Single, double chain, and sheet structures
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Def.: Solid Solutions
} Some ions can SUBSTITUTE for other similar sized and charged
ions
} Ex: (Fe,Mg)2SiO4
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Five mineral groups account for 90% of all of the Earth’
Earth’s
crust
}Feldspar
}Quartz
}Pyroxene
}Amphibole
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}Mica
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Feldspar, Quartz, Hornblende (amphibole)
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Mica
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Common silicate minerals
ÑOlivine
ß High temperature
ß Individual silicate tetrahedra linked by Fe and Mg
ß Small, rounded crystals with no cleavage
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Olivine
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Common Silicate minerals
ÑPyroxene Group
ß Single chain structures involving Fe and Mg
ß Two distinctive cleavages at nearly 90 degrees
ß Augite is the most common mineral in the pyroxene
group
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Common Silicate minerals
ÑAmphibole Group
ß Double chain structures involving a variety of ions
ß Two perfect cleavages exhibiting angles of 124 and 56
degrees
ß Hornblende is the most common mineral in the
amphibole group
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Cleavage angle for augite and hornblende
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Hornblende crystals
Microscopic hornblende crystal
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Common Silicate minerals
ÑMica Group
ß Sheet structures that result in one direction of perfect
cleavage
ß Biotite is the common dark colored mica mineral
ß Muscovite is the common light colored mica mineral
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Name?
Common Silicate minerals
ÑFeldspar Group
ß Most common mineral group
ß 3-dimensional framework of tetrahedra exhibit two directions of
perfect cleavage at 90 degrees
ß Orthoclase (potassium feldspar) and Plagioclase (sodium and
calcium feldspar) are the two most common members
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Potassium feldspar
Plagioclase feldspar
Common silicate minerals
ÑClay minerals
ß Clay is a general term used to describe a variety of
complex minerals
ß Clay minerals all have a sheet or layered structure
ß Most originate as products of chemical weathering
Clay mineral structure
Important nonsilicate minerals
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Oxide - Hematite
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Sulfide – name?
Sulfide – name?
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Native element – name?
Native element –name?
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Halide –name?
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Important nonsilicate minerals
}Carbonates
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ß Primary constituents in limestone and dolostone
ß Calcite (calcium carbonate) and Dolomite (calciummagnesium carbonate) are the two most important
carbonate minerals
Carbonate - Calcite
Important nonsilicate minerals
ÑMany nonsilicate minerals have economic value
ÑExamples
ß Hematite (oxide mined for iron ore)
ß Halite (halide mined for salt)
ß Sphalerite (sulfide mined for zinc ore)
ß Native Copper (native element mined for copper)
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Native Copper
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End of Chapter 2
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