PYROXENE MINERAL GROUP.pptx

INTRODUCTION
GENERAL FORMULA
CLASSIFICATION
SILICATE STRUCTURE
MODE OF OCCURRENCE
PHYSICAL PROPERTIES
OPTICAL PROPERTIES
USES
CONCLUSION

1. Pyroxene mineral group Name-Ranjeet Biswal Roll No-22GEOL-027 Class- M.Sc 1 st year utkal university,vani vihar Pg department of geology

2. contents: OPTICAL PROPERTIES

3. INDRODUCTION Mineral- A mineral is a naturally occurring homogenous substance which has a more or less definite chemical composition and definite atomic structure. The minerals are usually formed by inorganic processes . Example- q uartz,feldspar,olivine and calcite .

4. (Fig-Most abundants mineral in earth’s crust.) Pyroxene - The name pyroxene is derived from Greek words which means stranger to fire. Pyroxene was named because of its presence in glassy or vitreous lava. Pyroxene are constitute 11% of earth crust materials and hold’s 4 th position in abundance after plagioclase feldspar, alkali feldspar and quartz. Pyro - Fire Xenos - Stranger

5. Pyroxene are generally formed during early stage of magmatic period , when the temperature is very high . So therefore it have high density. It is formed after the formation of olivine. It is belong to discontinuous crystallization series. Pyroxene is mafic mineral . Pyroxene is very susceptible to chemical and physical weathering . BOWEN’S REACTION SERIES

6. General formula Here X represents ions of larger size, such as calcium(Ca),sodium(Na),iron(Fe) and magnesium(Mg). X Y ( SI 2 O 6 ) Y represents ions of smaller size, such as chromium(Cr), a luminium(Al),magnesium(Mg),manganese(Mn) and cobalt(Co ).

7. CLASSIFICATION Pyroxene is divided into two main group based crystal structure and chemical composition . ORTHOPYROXENE - Pyroxene that crystallize in the orthorhombic crystal structure . Example- Enstatite,Ferrosilite and Hyperthene . (Fig- Enstatite ) (Fig – Diopside ) CLINOPYROXENE - Pyroxene that crystallize in monoclinic crystal structure . Example- Diopside,Hedenbergite and Augite .

8. (Fig-Ternary diagram ) The figure shows wollastonite,enstatite and ferrosillite are the end member of pyroxene group.The mineral wollastonite, although used as an end member to describe pyroxene composition, is not a pyroxene.

9. THE ORTHOPYROXENE Enstatite = Mg SiO 3 Ferrosilite = Fe SiO 3 Hyperthene =(Mg Fe) 2 Si 2 O 6 Here complete solid solution exist between enstatite and ferrosilite. They are substitute for each other with 6 to 8 coordination site .

10. THE CLINOPYROXENE Diopside = Ca Mg Si 2 O 6 Hedenbergite = Ca Fe Si 2 O 6 Here solid solution exist between two end member clinopyroxene i.e diopside and hedenbergite.

11. SODIUM PYROXENE The sodium rich pyroxene is also crystallized in monoclinic crystal system ,so therefore it is belong to clinopyroxene group. The sodium pyroxene and iron bearing pyroxene are found in alkaline igneous rocks of various type. The sodium and aluminium bearing pyroxene occur primarily in igneous or metamorphic rocks formed under conditions of high pressure and temperature (eg-jadeite,ompacite )

12. SILICATE STRUCTURE Pyroxene minerals are comes under single chain (ionsilicates) silicate structure. Ionsilicate structure divided into two type. I - Single chain structure . II – Double chain structure .

13. SINGLE CHAIN STRUCTURE If two of the oxygens are shared in a way to make long single chains of linked SiO 4  tetrahedra, we get the single chain silicates or inosilicates. The ratio of silicon to oxygen in single chain silicate is 1:3 . (Fig - Single chain structure)

14. II. DOUBLE CHAIN STRUCTURE (Fig-Double c hain structure) Two single chains lie side by side by side so that all the right sided tetrahedrons of the left chain are linked by an oxygen to the left sided tetrahedrons of the right chains. The ratio of silicate to oxygen in double chain silicate is 4:11 .

15. MODE OF OCCURRENCE Pyroxene is the name of the group of dark colored rock-forming minerals found in igneous and metamorphic rocks throughout the world. They are most abundant in the dark colored igneous rock, such as basalt and gabbro , that comprise most of the oceanic crust. Pyroxenes are also important minerals in many peridotites rock( harzburgite , wehrlite)   . Rocks of the upper mantle are composed mainly of  olivine  and pyroxenes . Prroxene is also present in various type of metamorphic rock . The most important are – Granulite - Is a high grade metamorphic rock mostly composed orthopyroxene and clinopyroxene . Eclogite - It is a high temperature and high pressure metamorphic rock consists omphacite (high pressure c px and Na rich)and garnet. Pyroxenes are not abundant in sedimentary rocks because pyroxenes rarely form at low temperatures and are very susceptible to chemical and physical weathering.

16. PHYSICAL PROPERTIES OF PYROXENE Chemical classification – Silicate Color – Dark green to dark brown or black Streak – White Lusture – Vitreous to dull Diaphaneity – Semi-translucent to opaque Hardness – 5 to 7 Specific gravity – 3 to 4 Cleavage – Two set of cleavage Crystal system – Orthorhombic or monoclinic

17. OPTICAL PROPERTIES 2v – Biaxial 60˚-90 ˚ Colour- Mg rich opx are are colourless and, Fe rich show pale green to pale brown. Pleochroism- Colour opx show faint pleochroism . Cleavage- ~90˚ 2 sets (exact 87˚-93˚) Relief- Moderate(En) to high( Fs ) Birefringence-1 st order colour ( opx ), 2 nd order colour ( cpx ) Extinction- Parallel extinction of minerals such as orthopyroxene. Habit- Early formed opx in igneous rock appear as short prismatic crystal.

18. USES OF PYROXENE ( Fig – Crush trap rock ) ( Fig – Chromo diopside ) Pyroxene mineral are minor to secondary components of some rock that are use as crushed stone . A few pyroxene are used as gem material . It is also used as construction industry and decorative tile and facing stone .

19. REFERENCES.. Mineralogy- Dexter Perkins Rutleys Elements Of Mineralogy- C.D Gribble Earth Materials –Kevin Hefferan https:// geology.com/minerals/pyroxene.shtml https:// www.alexstrekeisen.it/english/pluto/pyroxene.php

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