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.

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

14. CRYSTALOGRAPHY-TRICLINIC
SERIES
ALBITE- 0-10% AN
OLIGICLASE-10-30%AN
ANDESINE-30-50%AN
LABRADORITE-50-70%AN
BYTWOWNITE-70-90%AN
ANORTHITE-90-100%AN

15. Albite
AlbiteOligoclase

16. Andesine
Labradorite
Bytownite
Anorthite

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

27. SUNSTONE
MOONSTONE
ORTHOCLASE
OLIGOCLASE

28. MINERALOGY-DEXTER PERKINS
INTRODUCTION TO MINERALOGY-WILLIAM D.NESSE
AN INTRODUCTION TO ROCK FORMING MINERALS-
J.ZUSSMAN
GOOGLE.COM
REFERENCE