Feldspar Group Of Minerals in geology.pptx

Feldspar Group Of Minerals in geology.pptx

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  Feldspar Group Of Minerals PresentedBy, Meenakshi A MSc Geology
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  Introduction Feldspars are themost common rock forming mineral.  Feldspars make up more than half of Earth’s crust. Word feldspar is derived from German words : FELD + SPAR Feld : field and Spar : light colored minerals that break with a smooth surface. Common rock forming mineral in igneous and metamorphic and sedimentary rocks.
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  • The silicatestructure is Frame Work or Tecto-silicate structure also known as 3-D structure. • Feldspars are Aluminosilicate minerals with the general formula : XAl Si O . where X can be Na/K/Ca. Structure of Feldspars 1-2 3-2 8 • The structure contains SiO4 and AlO4 tetrahedrons • Each tetrahedron consists of a central Silicon/Aluminum atom bonded to four oxygen atoms. • Si and Al tetrahedrons are arranged to form 4 membered rings.
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  Structure of Feldspars
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  • These 4membered rings are joined together to form Crankshaft Structure. Structure of Feldspars
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  Structure of Feldspars
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  • The crankshaftstructure created Voids. • The positively charged cations: Na/K/Ca that occupy relatively large Voids/Intersticies in the frame work structure. Structure of Feldspars
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  Structure of Feldspars
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  COMPOSITION • Feldspars include3 principal end members: 1) Albite 2) Anorthite 3) K-feldspar • Compositional range between albite and anorthite is : Plagioclase feldspar AND Between K-feldspar and Albite is Alkali feldspar. : NaAlSi3O8 : CaAl2Si2O8 : KAlSi3O8
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  Ternary Diagram ShowingCompositional Range Of Feldspars
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  Alkali feldspars Feldspars withcomposition ranging from: KAlSi3O8 – NaAlSi3O8 Members include : Microcline Sanidine Anorthoclase Orthoclase Adularia
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  Alkali feldspars Formation ofdifferent alkali feldspars based on cooling rate.
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  PHYSICAL PROPERTIES • Form/Habit :Usually prismatic, also tabular and elongated. Colour : Flesh red, pink, light pink or red. • Streak : White • Lustre : Vitreous • Cleavage : Perfect two directional • Fracture : Uneven. • Hardness : 6 • Specific Gravity : 2.57 Alkali feldspars
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  PHYSICAL PROPERTIES Crystallographic system : Alkali feldspars
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  Plagioclase feldspars Feldspars withcomposition ranging from: NaAlSi3O8 – CaAl2Si2O8 Members include : Albite (Ca%0-10 – Na%100-90) Oligoclase (Ca%10-30 – Na%90-70) Andesine (Ca%30-50 – Na%70-50) Labradorite (Ca%50-70 – Na%50-30) Bytownite (Ca%70-90 – Na%30-10) Anorthite (Ca%90-100 – Na%10-0)
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  PHYSICAL PROPERTIES Form/Habit : Usuallyprismatic, also tabular Colour : Variable, usually white or light coloured, also grey and colourless Streak : White Lustre : Vitreous, semi-vitreous to pearly Cleavage : Two directional Fracture : Uneven and splintery Hardness : 6.0 - 6.5 Specific Gravity : 2.55 - 2.76
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  Uses Of Feldspars • Feldsparsare used widely in the glass and ceramics industries. • In addition, several feldspars are used as gemstones. For example, moonstone. • Amazonite, a green variety of microcline, is used as an ornamental material. • Used in paint, fabrics etc.
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  References Earth Materials 2ndEdition Nesse Rutley’s Elements of Mineralogy Wikipedia Study.com
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  Thank You All Presentedby, Meenakshi A MSc Geology Year One Email [email protected]