The pyroxene group of minerals03
- 1. THE PYROXENE GROUP OF MINERALS
- 4. Silicate Structure Of Pyroxenes The pyroxene group of minerals is in the INOSILICATE subdivision of the silicates group Inosilicates - Group of silicate minerals that have their tetrahedrons form single or multiple chains, with two oxygen atoms of each tetrahedron part of its neighboring tetrahedron forming long, thin, chains. Si: O =1:3.
- 5. INOSILICATE STRUCTURE Divided into two types: Single Chain Structure Double Chain Structure
- 8. Single Chain Inosilicate Structure
- 9. Double Chain Inosilicate Structure
- 12. This difference produces a difference in angles The cleavage of the two groups results between chains and does not break the chains thus producing prismatic cleavage In the single chained silicates the two directions of cleavage are at 87° and 93° (close to 90 degrees) forming nearly square cross sections In the double chain silicates the cleavage angles are at 56° and 124° (close to 120 and 60 degrees) forming rhombic cross sections
- 13. This makes it a convenient way to distinguish between single chain and double chain silicates or more precisely between pyroxene minerals and amphibole minerals The amphiboles contain the same elements that the pyroxenes do, except they have hydroxyl (OH) in their structure, which alters both its physical and chemical properties For example:- Augite- (Ca,Mg,Fe)SiO 3 Hornblende- Ca 2 (Mg, Fe, Al) 5 (Al, Si) 8 O 22 (OH) 2
- 15. Clino pyroxene group Clino pyroxene (Diopside series) Diopside Ca Mg Si2 O6 Hedenbergite Ca Fe Si2 O6 Pyroxene Solid solutions Pigeonite (Ca, Mg, Fe)2 Si2 O6 Augite (Ca, Mg, Fe, Na) (Mg, Fe, Al) (Si, Al)2 O6 Omphacite (Ca, Na )(Fe Mg Al) (Si, Al)2 O6 Aegirine Na (Al, Fe3+) Si2 O6 Na and Li pyroxenes Jadeite Na Al Si2 O6 Spodumene Li Al Si2 O6
- 16. General formula (w,x,y)2 Z2 O6 In which w, x, y, z indicate elements having similar ionic radii and capable of replacing each otherin the structure. W= Ca, Na X= Mg, Fe2+, Mn, Li Y= Al, Fe 3+, Ti Z= Si, Al
- 17. Diopside- hedenbergite Complete solid solution exist between diopside and hedenbergite and johannssenite (Ca Mn Si2 O6) Diopside is the most common pyroxene. Found in mafic and ultramafic igneous rocks. Found in marbles associated with calcite, quartz or forsterite, tremolite and garnet. Also found in medium and high grade metamorphosed mafic rocks. Hedenbergite is often found associated with ore deposits formed at high temperatures
- 18. AUGITE
- 19. AEGIRINE
- 20. DIOPSIDE
- 22. Enstatite- Ferrosilite Enstatite Mg Si O3 Ferrosilite FeSiO3 Hypersthene& Bronzite (Mg, Fe)2 Si2 O6. Enstatite usually massive , blocky, fibrous or lamellar. Individual crystals may be prismatic or acicular. Complete solid solution exist between Enstatite- Ferrosilite Except at high temperature, only limited solid solution exist between clino pyroxene end members diopside and heldenbergite.
- 23. Enstatite- Ferrosilite Enstatite 0-10(% Fe) Bronzite 10-30 Hypersthene 30-50 Ferrohypersthene 50-70 Eulite 70-90 Orthoferrosilite 90-100
- 24. Occurrence and associations Enstatite is more common in mafic igneous rocks. Commonly associating with plagioclase and clinopyroxene Also in high- grade metamorphic rocks and is considered diagnostic for the granulite facies . Hypersthene is a characteristic mineral associated with charnockite series of rocks. Eulite and Orthoferrosilite- associated with fayalite, hedenbergite, grunerite and almandine – spessartine garnet, of eulysite, a regionally metamorphosed Iron rich sediment.
- 25. Augite Most common pyroxene found in mafic to intermediate igneous rocks, both plutonic and volcanic Associated with hornblende and plagioclase Augite is equivalent to diopside with may impurities, especially Na. Omphacite is a bright green variety of augite rich in Na and Al.
- 26. Jadeite The term jade refers to either jadeite or to the amphibole, nephrite. It is a high pressure pyroxene found in metamorphic rocks of the blueschist facies. Associated with glaucophane, lawsonite or aragonite, and with quartz and epidote. A bright green variety of jadeite, omphacite, occurs in eclogites with pyrope rich garnets. Omphacite is also found in kimberlites.
- 27. Spodumene Spodumene found in granitic pegmatites, where it associated with k- feldspar, quartz, muscovite, tourmaline, beryl and lepidolite. Hiddenite is a name given to emerald green spodumene. Kunzite to lilac/pink colour spodumene. Triphane to colourless or yellow spodumene.
- 28. ENSTATITE
- 29. FERROSILITE
- 30. HYPERSTHENE
- 31. THE END