Felspar group
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This document provides a summary of alkali feldspar and plagioclase feldspar. It discusses their crystal structure, composition, physical and optical properties, paragenesis, and applications. Alkali feldspar includes orthoclase, sanidine, and microcline. Plagioclase feldspar is a solid solution between albite and anorthite. Both have important industrial uses such as in ceramics, glass, paints, plastics, and as gemstones. The document is presented by Atish Kumar Sahoo for his MTech course at the Department of Applied Geology.
Felspar group
- 1. PRESENTED BY- NAME-ATISH KUMAR SAHOO MTECH 1ST YEAR(2018-19) 1ST SEMESTER DEPARTMENT OF APPLIED GEOLOGY REGISTRATION NO-Y18251009 GUIDED BY DR.G.C. GAUTAM
- 2. SYNOPSIS • INTRODUCTION • STRUCTURE • ALKALI FELDSPAR COMPOSITION • PHASE DIAGRAM • PHYSICAL AND OPTICAL PROPERTIES K-FELDSPAR • PARAGENESIS OF K-FELDSPAR • PLAGIOCLASE FELDSPAR COMPOSITION • ZONING • PHYSICAL AND OPTICAL PROPERTIES OF PLAGIOCLASE FELDSPAR • PARAGENESIS OF PLAGIOCLASE FELDSPAR • APPLICATIONS • REFERENCES
- 3. It is derived from GERMAN word. Feld=field and spar=light colour mineral that break with a smooth surface. Most common rock forming mineral in Earth crust. Most common constituent in igneous rock. FELDSPAR are essential component in igneous, metamorphic and sedimentary rock. Classification based on its content. Most of the product we use every day made with feldspar.
- 4. • X Al(1-2) Si(3-2) O8 • The X in the formula can be K &/or Ca &/or Na
- 5. STRUCTURE Structure of feldspar consists of a framework of corner sharing si-al tetrahedral. Rings are formed crankshaft like chains.
- 6. ionic radius Charge balance Ordering of Al-Si tetrahedra (temperature and no. of Al necessary to maintain charge balance)
- 7. Feldspar may derive into two compositional series Alkali feldspar (solid solution between ORTHOCLASE and ALBITE) Plagioclase feldspar (solid solution between ALBITE and ANORTHITE) TERNARY DIAGRAM OF FELDSPAR GROUP
- 8. MONOCLINIC ORTHOCLASE,SANIDINE,ADULARIA TRICLINIC MICROCLINE,ANORTHOCLASE • It is due to displacive trasformation • Sifting of atomic position • Bending of bond angle
- 10. Diagram showing alkali feldspar polymorphs stable at different temperatures No single mineral is stable under this particular P-T condition UNMIX OF TWO END MEMBER at low temp. o PERTHITE-Irregular veins,patchs,lenses of Na feldspar in K-feldspar o ANTIPERTHITE-OPPOSITE to perthite EXSOLUTION
- 11. COLOUR- SEA GREEN MICROCLINE FLESH RED ORTHOCLASE HABIT-PRISMATIC AND TABULAR FRACTURE-UNEVEN LUSTURE-VITREOUS CLEAVAGE-PERFECT AT(001);GOOD AT(010) STREAK-WHITE TWINNIG- HARDNESS- 6 CARLSBAD SPECIFIC GRAVITY-2.54 TO 2.72 TWINNING
- 12. OPTICAL PROPERTIES (POTASH & ALKALI FELDSPARS) Properties Orthoclase Microcline Anorthoclase Color Colorless, Cloudy Relief Low - Moderate Twinning Carlsbad Cross - hatched Very Fine Cross - hatching Interference Color Grays of First Order Extinction Max. 21˚ Max. 15˚ ≈ 2˚ Optic Sign Biaxial (-ve)
- 13. ALKALI FELDSPAR IN IGNEOUS ROCK Important constituent of Acid and alkali rock They are generally found in granite ,syenite and their volcanic equivalents They are found in pegmatite rocks In plutonic rock orthoclase essentially present and in volcanic rock sanidine essentially present ALKALI FELDSPAR IN METAMORPHIC K-feldspar is stable product of thermal and regional metamorphism Microcline and sanidine are generally found as feldspar ALKALI FELDSPAR IN SEDIMENTARY ROCK These are found in sandstone,siltstone ,shale and sediments MINERAL IN GRANITE
- 17. ZONING IN PLAGIOCLASE FELDSPAR If equilibrium between crystal and melt is maintained results will be compositionally homogeneous crystals If equlibrium is not maintain a rim of new composition around the old one will be formed.
- 18. PLAY OF COLOUR DUE TO VERY FINE GRAIN EXSOLUTION LAMELLAE MANY LABRADORITE CRYSTAL SHOW PLAY OF COLOUR
- 19. COLOUR – WHITE TO GRAY LUSTURE-PEARLY TO VITRIOUS STREAK –WHITE HARDNESS-6 SPESIFIC GRAVITY-2.54-2.75 FRACTURE- UNEVEN CLEVAGE-2 SETS TWINING-POLYSYNTHETIC TWINNING TRASPARENCY-TRASPARENT TO TRASLUCENT POLYSYNTHETIC TWINNG(ALBITE)
- 20. OPTICAL PROPERTIES (PLAGIOCLASE FELDSPARS) Properties Albite Oligoclase Andesine Labradorite Bytownite Anorthit Color Colorless, cloudy Cleavage 2 sets, ≈ 90˚ Relief Low – Moderate, increases from Albite to Anorthite Twinning Albite Law Interference Color Gray of First Order Extinction 12˚ - 16˚ Only a few degrees 20˚ 27˚ - 37˚ 38˚ - 40˚ > 40˚ Optic Sign Changes with composition
- 21. IN IGNEOUS ROCK Most common in basalt In plutonic rock ANORTHITE,TRACTOLITE,TONALITE In PEGMATITE ALBITE is common IN GABBRO LABRADORITE is common In anorthosite anorthite is common IN METAMORPHIC ROCK Albite is essential constituent of metamorphic rock schist IN SEDIMENTARY ROCK Mostly in sedimentary rocks of near volcanic area.
- 22. ADULARIA LOW TEMP. ORCHOCLASE AMAZON STONE(AMAZONITE) BRIGHT GREEN MICROCLENE
- 23. AVENTURINE GEM V. OF ALBITE MOON STONE(ALBITE) PINK PLAGIOCLASE
- 24. Two properties which makes feldspar useful for downstream industry are alkai and aluminium contain Due to its attractive looking colour ,it is more useful CERAMIC: In manufacture of ceramics,feldspar is second most important ingredient after clay
- 25. Feldspar is used in Glass Industry for - 1. Due to its Alumina content which provide glass with hardness, durability and resistance to chemical corrosion. 2. Na2O and K2O are fluxes which reduce the melting temperatures of the quartz enabling control of the glass's viscosity, less energy is used and decrease the amount of soda ash needed. 3.70% of feldspar use is in Glass Industry. Paints / Plastic / Rubber: • Feldspars also are used as fillers and extenders in applications such as paints, plastics and rubber. • Beneficial properties of feldspars include good dispersbility, high chemical inertness, stable pH, high resistance to abrasion, low viscosity at high filler. • Loading, interesting refractive index and resistance to frosting . Welding: Feldspar are used in coatings of welding electrode for their fluxing properties,particularly for coating electrodes .
- 26. OTHER USES IN MILD ABRASIVES AS A WELDING ROAD CUTTIG ROAD AGGREGATE TABLE WERE AND MOST IMPORTANTIS -AS A GEMSTONE
- 28. MINERALOGY-DEXTER PERKINS INTRODUCTION TO MINERALOGY-WILLIAM D.NESSE AN INTRODUCTION TO ROCK FORMING MINERALS- J.ZUSSMAN GOOGLE.COM REFERENCE