Feldspar Group Of Minerals in geology.pptx

Feldspar Group Of Minerals in geology

1. Feldspar Group Of Minerals Presented By, Meenakshi A MSc Geology

2. Introduction Feldspars are the most common rock forming mineral.  Feldspars make up more than half of  Earth’s crust . Word fel dspar 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.

3. The silicate structure 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.

4. Structure of Feldspars

5. These 4 membered rings are joined together to form Crankshaft Structure . Structure of Feldspars

6. Structure of Feldspars

7. The crankshaft structure created Voids . The positively charged cations: Na / K / Ca that occupy relatively large Voids/ Intersticies in the frame work structure. Structure of Feldspars

8. Structure of Feldspars

9. COMPOSITION Feldspars include 3 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

10. Ternary Diagram Showing Compositional Range Of Feldspars

11. Alkali feldspars Feldspars with composition ranging from: KAlSi3O8 – NaAlSi3O8 Members include : Microcline Sanidine Anorthoclase Orthoclase Adularia

12. Alkali feldspars Formation of different alkali feldspars based on cooling rate.

13. 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

14. PHYSICAL PROPERTIES Crystallographic system : Alkali feldspars

15. Plagioclase feldspars Feldspars with composition 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)

16. PHYSICAL PROPERTIES Form/Habit : Usually prismatic, 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

17. Uses Of Feldspars Feldspars are 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.

18. References Earth Materials 2nd Edition Nesse Rutley’s Elements of Mineralogy Wikipedia Study.com

19. Thank You All