Olivine description of minerals

Olivine description of minerals

1. Dr. Harisingh gour vishwavidyalaya SAGAR, M.P (Central University) DEPARTMENT OF APPLIED GEOLOGY Under guidance of: Dr. G.C.Gautam Presented by: Nalini das Reg no:Y17251013

2. CONTENTS Introduction Members of olivine family Weathering Solid-solution Bowens reaction series Structure Alteration High pressure polymorph Spinifex texture Physical and optical property Paragenesis Significance References

3. Introduction Olivine is named due to its olive green color. Olivine are the important rock forming mineral This group consist of number of closely related mineral crystallized in orthorhombic system. Structure of the minerals of this group has independent tetrahedron linked by Sio 4 diavalant atom in 6-fold co-coordination.

4. The general formula of olivine series of mineral is R 2 sio 4 where R=mg or fe The members of this group belongs to continous solid-solution between forsterite and fayalite . The olivine is considered as mixture of two end member i.e (fo 63 fa 37 ) MEMBERS OF OLIVINE FAMILY

5. MINERALS OF OLIVINE Mg-Rich Forsterite (Mg 2 SiO 4 ) Fe-Rich Fayalite (Fe 2 SiO 4 ) Mn -rich Tephorite (Mn 2 SiO 4 ) Mn -Fe Rich Knebelite ( Mn,Fe ) 2 SiO 4 Ca- rich Larnite (Ca 2 SiO 4 ), Ca-Mg rich Monticellite ( Ca,Mg )SiO 4 Ca-Fe Rich kirschsteinite ( Ca,Fe )SiO 4

6. WEATHERING Fig:www.google / blogspot

7. Solid-solution Fig- www.google / blogspot

8. Why forsterite and fayalite form solid-solution series? The two minerals form solid solution only when atomic size difference between two minerals should be less then 15. The mineral which form solid-solution should have similar crystal structure. The electro negativity difference should be very less. if E.N is high there may be chances of compound formation. Valency of this compound should not be widely difference.

9. How it is derived The ultramafic rock such as peridotite and dunite after partial melting produce olivine. The metamorphism of impure dolomite or other sedimentary rock with high magnesium and low silica can produce mg rich olivine or forsterite . Why mg rich olivine does not occur with silica? Firstly mg rich olivine crystallized at temperature of about 1900 c where silica crystallized 573 c so there is no doubt,they never occur together. Secondly if they occur together then they form orthopyroxinite which they never wants to be change.

10. BOWENS REACTION SERIES Fig:www.google / wikipedia

11. The structure of olivine was proposed by Bragg and Brown. The structure consist of indivisual si -o tetrahedron linked by mg or fe atom each of which has 6 nerest oxygen atom. STRUCTURE

12. The alteration mechanism involves the diffusion of hydrogen ion into olivine structure which enable oxygen ion to release mg,fe 2+ and Si ions from there sites and allow fe 3+ Al and Ca to fulfill the space. Serpentinization is the most widespread form of olivine alteration. 2Mg 2 Sio 4 +3H 2 O=Mg 3 si 2 O 5 (OH) 4 +Mg(OH) 2 3Mg 2 Sio 4 +4H 2 o+Sio 2 =2Mg 3 Si 2 O 5 (OH) 4 The main alteration products are brucite,talc and carbonates. ALTERATION

13. Fig:www.google / blogspot DURING ALTERATION OLIVINE CHANGES TO SERPENTINE

14. With high temperature and pressure found at depth the olivine structure is no longer stable. Below depth about 410 km(250mi),olivine undergo exothermic phase transition to the mineral wadsleyite and at about 520km(320mi), wadsleyite transfer into Ringwoodite which has spinel structure. And at depth about 660km (410mi), Ringwoodite decompases into silicate Pervoskite ( Mg,Fe )sio 3 These phase transition leads to discontinious increase in density of earth surface which can be measure by seismic method. HIGH PRESSURE POLYMORPH

15. The term spinifex was introduced by Lewis and Nesbitt(1971).The name is came from spinifex plant of Western Australlia . It consist of long acicular phenocryst of olivine which give rise to bleaded appearance. mechanism we know that olivine has crystal structure of independent tetrahedron i.e Nesosilicate structure. So it is difficult to get into glass phase during sudden cooling or quenching. So long acicular of phenocryst (olivine) are found in spinifex texture. SPINIFEX TEXTURE

16. Images of spinifex texture Fig:www.google / wikipedia

17. FORSTERITE PHYSICAL PROPERTY : COLOUR : GREEN, STREAK : WHITE, LUSTER : VITREOUS, FRACTURE:CONCOIDAL CLEVAGE : POOR: HARDNESS : 6.5, SPECIFIC GRAVITY :3.2, TRANSPARENCY : TRANSLUCENT; Fig:www.google / blogspot PHYSICAL AND OPTICAL PROPERTY OF OLIVINE

18. UNDER PPL: COLOUR: COLOURLESS, FORM:PRISMATIC; RELIEF:HIGH; R.I.:HIGH; PLEOCHROISM:NO; UNDER CROSS NICOL: OPTICAL CHARCTER:ANISOTROPIC; INTERFERENCE COLOUR:THIRD ORDER; EXTINCTION:PARALLEL; ALTERATION:SERPENTINE ; Fig:www.google / blogspot THIN SECTION OF FORSTERITE

19. PHYSICAL PROPERTIES COLOUR : YELLOW STREAK : WHITE HARDNESS : 6.5 LUSTRE : VITREOUS SPECIFIC GRAVITY:4.4 CLEAVAGE : POOR; fig:www.google / blogspot FAYALITE

20. OPTICAL PROPERTY UNDER PPL COLOUR:YELLOW, PLEOCHROISM:WEAK, R.I.:HIGH RELIEF:HIGH, UNDER CROSS NICOL OPTICAL CHARACTER:ANISOTROPIC, INTERFERENCE COLOUR:THIRD ORDER, EXTINCTION:PARALLER EXTINCTION ALTERATION:ALTER TO SERPENTINE; Fig:www.google / blogspot THIN SECTION OF FAYALITE

21. Mg rich olivine also discorved in meteorites on the Moon and Sun . Such meteorites include condrites which is the collection of dabris from early solar system. The meteorite of pallasites also discorved which is the mixture of iron,nickel and olivine EXTRATERRASTRIAL OCCUARANCE Fig:www.google / blogspot

22. Oivine is the major constituent of dunite and peridotite . More iron rich olivine occur in basic rock and sometimes in volcanic rock it occurs as phenocryst and groundmass. Under anhydrous condition,diopside react with silica to form magnesium rich olivine. 2CaMg(CO 3 ) 2 +Sio 2 =Mg 2 Sio 4 +2CaCo 3 +2Co 2 Fe rich olivine rare in amount and occur granite and rhyolite and extrmely Fe rich olivine stable with quartz. PARAGENESIS

23. Olivine also called as mineral of “gemstone” which is known as “ peridot ”. It is yellow green to green color and servs as brithstone for the month of august. Most olivine used in metallorgical process as slag conditionar . High magnesium olivine( forsterite ) is added to blast furnaces to remove the the impurities from sleel and form a slag. Olivine has also been used as refractory materials.It is used to make refractory brick and used as casting sand. SIGNIFICANCE

24. Green sand beaches has green color due to its presence Ex. Papacolea beach in Hawaii Olivine is easily altered. Fe and Mg released make the soil fertile. GEOLOGICAL SIGNIFICANCE Fig:www.google / blogspot

25. Most world peridot used in ornamental purpose are mined at Sancarlos Reservation in Arizona. Higher quality and larger peridot crystal are mined at Pakisthan and Myanmar . Olivine also found at Kerali area of Abujhmar Basin in Bastar craton madhya pradesh OCCUARRANCE

26. OLIVINE DUNITE Fig:www.google / wikipedia

27. OLIVINE IN BASALT Fig:www.google / blogspot

28. OLIVINE IN RHYOLITE Fig:www.google / blogspot

29. REFERENCES Alexander P.O, A handbook of minerals, crystals, rocks and ores . J Zussman,An introduction on the rock forming mineral . Karr P.F, Mineral optics. Perkins Dexter, Mineralogy, 3 rd edition, PHI Learning Private Limited. www.google/blogspot www.google/wikipedia