Feldspar- An important rock forming mineral

FELDSPAR MINERAL

1. FELDSPARS : AN IMPORTANT ROCK FORMING MINERAL GROUP Guided By Presented By Dr. NARENDRA JOSHI SONAM CHOUHAN Class – M.Sc. ( I Sem.) Govt. Holkar Science College Indore (M.P.) 03/10/2019 1

2. CONTENT 03/10/2019 2 INTRODUCTION CLASSIFICATION CRYSTLLOGRAPHICALLY 2.ON THE BASIS OF TEMPERATURE 3.ON THE BASIS OF CHEMICAL COMPOSITION ALKALI FELDSPAR GROUP PLAGIOCLASE GROUP CONCLUSION REFERENCE

3. INTRODUCTION 03/10/2019 3 The feldspar group approximates ternary system and may be considered of three components: orthoclase, Or=KALSi3; albite AB=NaALSiO8; and anorthite, An= CaAl2Si2O8. Or and AB from the alkali feldspar group, with An absent or a minor constituent. An form the plagioclase group where a range in composition may occur from 100 percent. Feldspar is the most common rock forming mineral (60%of the earth’s crust) The mineral name feldspar is derived from the German words feld+spar the word “ feld” is “field” in German and spar” is a term for light coloured minerals that break with a smooth surface. It is more commonly fount in Igneous and metamorphic rocks. Feldspar minerals are essential components in Igneous, metamorphic and sedimentary rocks to suck an extent that the classification of a number of rocks is based upon feldspar content.

4. 03/10/2019 4 FELDSPAR

5. CLASSIFICATION 03/10/2019 5 1. On the basis of Crystallography : The optical properties of the feldspars are ordinarily oriented with respect to crystallographic direction. (1.1) Monoclinic feldspar:-Monoclinic feldspar crystals may be illustrated by orthoclase. (1.2) Triclinic feldspar :- Triclinic feldspar crystals of the plagioclase group may be illustrated by albite.

6. Classification 03/10/2019 6 2. On the basis of temperature : 1. High temperature feldspar: when correlated with X- ray data and composition the optic angles for the alkali feldspars indicate high temperature division containing. Example : Anorthoclase, sanidine, albite. 2. Low temperature feldspar : Low – temperature albite constitute a low- temperature group. Example : Orthoclase, microcline. 3. On the basis of chemical composition: 1 Alkali feldspar MONOCLINIC COMPOSITION Orthoclase ( KNa ) AlSi3O8 Sanidine ( KNa ) AlSi3O8 Adularia ( KNa ) AlSi3O8 TRICLINIC Microcline ( KNa ) AlSi3O8 Anorthoclase ( KNa ) AlSi3O8

7. CLASSIFICATION 03/10/2019 7 2 Plagioclase group Triclinic Composition Ab An 100 0 Albite 90 10 Oligoclase 70 30 Andesine 50 50 Labradorite 30 70 Bytownite 10 90 Anorthite 0 100

8. Alkali feldspar group 03/10/2019 8 The alkali feldspar of volcanic rocks is frequently sanidine , while plutonic rocks yield orthoclase ,microcline is a common constituent of pegmatites while adularia may be a vein mineral High and low temperature group of alkali feldspars has been distinguished by Makenzie and smith (1956) Higher temperature group:- Cryptoperthitic Lower temperature group:- Microperthitic SODIUM FELDSPAR :- Glass :-It is of the most important raw materials needed when manufacturing glass .It acts as a fluxing agent that controls the viscosity of the glass. Ceramics :-After clay feldspar is the second most important raw material manufacturing ceramic .It can make the ceramic more tough and durable . FILLERS :- Because of its incomparable dispersibility .It can become good filler for points rubber and plastics.

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10. 03/10/2019 10 ENAMEL FRITS AND GLAZES :-Feldspar can assist in the composition of enamel that can help in making the finish of the product neat and spotless. PALASH INTERNATIONAL IS THE BEST :- Feldspar manufactures in India. ORTHOCLASE :- Orthoclase or orthoclase feldspar is an important tectosilicate mineral which form Igneous rock. 1.1 Physical properties :- Chemical composition potash Aluminium silicate. crystal system- monoclinic colour:- colourless pink ORTHOCLASE ORTHOCLASE

11. 03/10/2019 11 Form: prismatic Lustre :-Vitreous Cleavage:-2 sets cleavage Fracture:-Uneven Hardness:-6 streak:- White specific gravity:-Low(2.5) Diagnostive properties:-Cleavage -2 sets Colour- Colorless Origin:- Igneous –This potash combines with a lot of rocks Occurrence:-Orthoclase is the characteristic potash feldspar of igneous rocks ,occurring both alone and in perthitic intergrowth with albite. It also occurs in metamorphic rocks OPTICAL PROPERTIES UNDER ORDINARY & POLARISED LIGHT Colour-Colourless, Form-Granular, Cleavage -2 sets Relief-Moderate, Isotropic/Anisotropic- Anisotropic, Order of colour-First order. Under crossed Nicol position Extinction angle -5° – 12° ,Twinning –Simple Alteration –sericite ,Occurrence - It is occasionally found in Granite pegmatites and also in some metamorphic rocks.

12. Sanidine 12 PHYSICAL PROPERTIES :-chemical composition-Potash aluminium silicate ,crystal system –Monoclinic ,Colour –Colourless ,pink Form –prismatic ,cleavage-2 sets ,Lustre-vitreous ,Fracture –Uneven ,Hardness-6, Streak –white Specific gravity –low Diagnostic properties– Cleavage-2 sets ,Hardness-6,Colour – Colourless, Occurrence:-Sanidine occurs in potash rich volcanic rocks such as rhyolite and trachyte. FIG 4 SINIDINE

13. Optical properties 03/10/2019 13 PROPERTIES UNDER ORDINARY /POLARISED LIGHT :-Colour-colourless in thin sections. Form-Subhedral sanidine usually occurs in distinct crystals as phenocrysts .Cleavage -2sets perfect parallel. There may also be parting parallel. Relief-Low balsam. CROSSED NICOL POSITION :-Anisotropic, Order of colour –First order Extinction angle –parallel sections normal to an optic axis remain practically dark since the axial angle is often very small. Twinning –Usually according to the Carlsbad law. Occurrence-Sanidine has been generally considered characteristic of volcanic rock in plutonic rocks as well .

14. Adularia 03/10/2019 14 ADULARIA :-Adularia is probably a variety of orthoclase but is treated separately because of genetics significance THE OPTICAL PROPERTIES :-Adularia correspond to those of orthoclase ,but the crystal habit is pseudo –orthorhombic with a rhombic cross section .The is narrow or absent . Adularia is a rather low temperature feldspar found in veins and re- placement deposits, and in some rocks of low –grade metamorphism .It is especially characteristic of tertiary gold and silver ores of the bonanza types .The crystals are commonly minute and can be identified only with a rather high –power objective .X-ray study indicates a triclinic phase and Chemical composition.

15. Microcline 03/10/2019 15 MICROCLINE :-. Chemical composition -Potash Aluminium silicate . crystal system -Triclinic , colour -White, green ,pink Form –prismatic ,. cleavage -2 sets lustre -Vitreous ,Fracture –Uneven, Hardness -6-6.5 . streak –White . Specific gravity- Low(2.56 ),.diagnostive property -Hardness -, cleavage -2 sets , Colour -White, green, pink Occurrence- Microcline is the common potash feldspar of pegmatite and hydrothermal veins .It also occurs in metamorphic rocks . MICROLINE

16. microcline 16 OPTICAL PROPERTIES :- Under ordinary /polarised light :-Colour-Colourless in thin sections but may be cloudy on account of incipient alteration .Form –Microcline is usually found in subhedral to anhedral crystals. .cleavage –Perfect parallel. Relief -Low CROSSED NICOL POSITION:- . Isotropic /Anisotropic -Anisotropic,. Order of colour –Frist order,. Extinction angle -5°-15°.T winning –Polysynthetic ,Intergrowth –Albite is commonly intergrowth with microcline so that the direction are parallel .This intergrowth is known as perthite . Diagnostic properties –Cross hatched. . Occurrence- Microcline occurs in some granites ,syenites ,and gneisses .In perthite it is the principal feldspars of granite pegmatites .It is also a common mineral in sandstones , arkoses .

17. Anorthoclase 03/10/2019 17 PHYSICAL PROPERTIES:- Chemical composition –Sodium –aluminium silicate , Crystal system –Triclinic . colour- colorless ,also white, pale creamy yellow, red green Cleavage .–perfect on ,other partings.. luster -Vitreous to pearly Fracture- Uneven, prismatic pinacoidal, Tenacity -Brittle, specific gravity- Low, Hardness -6.

18. Plagioclase group 18 The plagioclase minerals constitute an important group for which an unusual number of optical methods have been developed to aid in study and identification .These are physical methods illustrated in test figure and diagrams . ALBITE:- Chemical composition -Sodium aluminium silicate . crystal system – Triclinic , Colour –White ,Reddish ,Gray. , Form – prismatic ,Cleavage -2 sets , Lustre –Vitreous Fracture –Uneven Hardness-6-6.5 ,Streak –White ,Specific gravity –Low diagnostic properties – Hardness – 6-6.5 , Colour –White Reddish ,Gray , Occurrence –Albite occurs in some igneous rock but more common in pegmatite

19. Albite Optical properties 03/10/2019 19 UNDER ORDINARY /POLARISED LIGHT :-Colour-Colourless in thin section Form –Albite occurs in plates or lath –shaped ,rarely in phenocrystal ,Cleavage-perfect ,less perfect ,imperfect ,Relief-Low CROSSED NICOL POSITION :-Isotropic /Anisotropic-Anisotropic ,Order of colour –First order ,Extinction angle –The maximum extinction angle in albite twins varies from 15°to 19° ,Twinning –Polysynthetic according to the albite law is rarely absent .Occurrence –Albite occurs in some granites ,in granite pegmatites ,in veins ,and in some metamorphic rocks .

20. Oligoclase ,labradorite and anorthite 03/10/2019 20 PHYSICAL PROPERTIES :- Chemical composition –sodium calcium aluminium silicate , Crystal system –Triclinic. Colour –colourless ,pink ,. Form –prismatic ,Tabular cleavage -2 sets, Lustre –Vitreous , Fracture –Uneven . Hardness - 6 streak –White specific gravity –Low Diagnostic properties –Hardness-6 Cleavage -2 sets Lustre –Vitreous

21. OPTICAL PROPERTIES Oligoclase, labradorite and anorthite 03/10/2019 21 UNDER ORDINARY /POLARISED : -Colour –Colourless thin section Form –Oligoclase occurs in euhedral ,subhedral ,and anhedral crystal , Cleavage- Perfect Relief- Low Extinction –The maximum extinction in albite twins 0° to 12° Isotropic/Anisotropic – Anisotropic Twinning – Polysynthetic as in albite Occurrence –Oligoclase is very common in persilicic igneous rock such as granites and rhyolites ,also in syenites ,trachytes ,and other igneous rocks .

22. 03/10/2019 22 References READ H. H. RUTLEY ELEMENTS OF MINERALOGY 27 TH EDITION KERR P. F. OPTICAL MINEROLOGY ( 3 RD EDITION) McGRAW HILL BOOK COMPANY INC. NEWYORK, TORONTO, LONDON (PG. NO. 248 to 282)

23. 03/10/2019 23 THANK YOU