PYROXENE MINERAL GROUP
- 1. Pyroxene group of minerals 1
- 2. Introduction Silicate structure of Pyroxene group Classification of Pyroxene group Orthorhombic Pyroxenes Monoclinic Pyroxenes Pyroxenoids Paragenesis References 2
- 3. Pyroxenes are the most important group of rock forming ferromagnesiam silicates , and occur as stable phases in every type of igneous rock. They are also found in many rocks of widely different compositions formed under the conditions of both thermal and regional metamorphism. The name pyroxene is derived from the Greek pyro, meaning “fire,” and xenos, meaning "stranger", and was given by Haüy to the greenish crystals found in many lavas which he considered to have been accidentally included there. 3
- 4. Pyroxenes have a basic structural unit consisting of linked SiO4 tetrahedra that each share 2 of their oxygens in such a way as to build long chains of SiO4.The basic structural group is thus Si2O6with. Pyroxenes have a general structural formula XYZ2O6 where, X = Na+, Ca2+, Mn2+, Fe2+, or Mg2+ filling octahedral sites Y = Mn2+, Fe2+, Mg2+ , Al3+, Cr3+, orTi4+ filling smaller octahedral sites Z = Si4+ or Al3+ in tetrahedral coordination. 4
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- 6. The pyroxene group of minerals is in the INOSILICATE subdivision of the silicate structures . Inosilicates - Group of silicate minerals that have their tetrahedrons form single or multiple chains , with two oxygen atoms of each tetrahedron part of its neighbouring tetrahedron forming long thin chains . Si:O=1:3 6
- 8. The pyroxenes may be divided for our purpose into the groups given below ; varieties based mainly on physical characters are considered under their appropriate chemical groups. I. Orthorhombic Pyroxenes ( orthopyroxenes ) II. Monoclinic Pyroxenes ( clinopyroxenes ) 8
- 10. The Pyroxenes which crystallizes in orthorhombic crystal system are known as orthopyroxenes. Orthopyroxenes typically occur as fibrous or lamellar (thin- plated) green masses in igneous and metamorphic rocks and in meteorites. These minerals differ in the ratio of magnesium to iron in the crystal structure; their composition ranges from pure magnesium silicate (MgSiO3) to pure ferrous iron silicate (FeSiO3). 10
- 11. Composition - MgSiO3 Crystal system – Orthorhombic Common form – Prismatic crystals massive & lamellar Cleavage -Two sets of cleavage planes which intersect at 90° Colour - Grey, green, brown, yellow, Dark green Lusture -Vitreous, pearly Hardness - 6 Specific gravity -3.1 to 3.3 Mode of occurrence - As a common constituent of igneous & metamorphic rock. Uses - As a Gemstone 11
- 12. Composition - MgFeSiO3 Crystal system – Orthorhombic Common form – Prismatic crystals are rare usually massive or foliaceous Cleavage -Three sets of cleavage in transverse section Colour - Commonly green, olive green to greenish black Lusture - Vitreous, pearly Hardness - 6 Specific gravity - 3.1 to 3.3 Mode of occurrence – As a common constitute of volcanic igneous rock like andesite and trachytes. Uses - As a gemstone 12
- 13. Composition - FeSiO3 Crystal system – Orthorhombic Common form – Prismatic crystals are rare. usually massive or foliaceous Cleavage -Three sets of cleavage in transverse section Colour - Grey, green, brown Lusture - Vitreous,pearly Hardness - 6 Specific gravity -3.1 to 3.3 13
- 15. Monoclinic Pyroxenes /Clinopyroxene (cpx) A group of Pyroxene minerals which crystallize in the monoclinic crystal system, including the calcium bearing clinopyroxenes and the sodium bearing pyroxenes. Important members of the group include augite, diopside,jadeite, pigeonite and aegirine. There are several series amongst the monoclinic pyroxenes. The first group of monoclinic pyroxenes,the Diopside hedenbergite series , is non- aluminous, whilst the augite series contains alluminium; the alkali pyroxenes are characterized by containing soda. 15
- 16. 16 A.Diopside – Hedenbergite Series
- 17. Composition - MgCaSi2O6 Crystal system – Monoclinic Common form – Prismatic crystals usually granular Cleavage - Good parallel Colour -White, green, Dark green Lusture - Vitreous Hardness - 6 Specific gravity -3.2 to 3.8 Mode of occurrence - Uses - Diopside has potential uses in ceramics, glass-making, biomaterials, nuclear waste immobilization, and fuel cell technology. 17
- 18. Composition - CaFeSi₂O₆ Crystal sys. - Monoclinic Common form - Crystals lamellar masses Cleavage - Good parallel Colour - Green to dark green, Brownish-green, Brown, Gray, Black Lusture -Vitreous Hardness - 6 Mode of occurrence – It occurs in metamorphosed iron rich sediments ,and is found in skarns and in rocks called eulysites. Specific gravity - 3.7 18
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- 20. Composition - (Ca,Mg,Fe,Al)2(Si,Al)2O6 Crystal sys. -Monoclinic Common form -Crystals coarsely lamellar sometimes granular or fibrous Cleavage - Prismatic cleavage good nearly 87° Colour - Black, brown, greenish Lusture -Vitreous Hardness - 6 Specific gravity - 3.2 to 3.5 Diagnostic character -Two cleavage angles nearly of 90 ° specific gravity Mode of occurrences - It is a common mineral of igneous rocks Uses - In studies of the temperature history. 20
- 21. Composition - (Ca,Mg,Fe)(Mg,Fe)(Si,Al)2O6 Crystal sys. - Monoclinic Common form - Prismatic crystals , granular Cleavage - good nearly 87° Colour - Black, brown, greenishbrown Lusture -Vitreous Hardness - 6 Specific gravity - 3.17 to 3.46 Mode of occurrence - Pigeonite occurs in rapidly chilled igneous rocks. 21
- 22. C. Alkali – Pyroxenes 22
- 23. Composition - NaFeSi2O6 Crystal sys. - Monoclinic Common form - Short Prismatic Crystals with blunt terminations, acicular crystals also occurs Cleavage - good nearly 87° Colour - Black, brown, greenish brown Lusture -Vitreous Hardness - 6 Specific gravity - 3.17 to 3.46 Mode of occurrence -Aegirine occur in late crystallizing products of alkali magmas. Uses - Gemstone 23
- 24. Composition - NaAlSi2O6 Crystal sys. - M0n0clinc Form -Prismatic crystals Usually massive Cleavage - Prismatic at 90° Colour - Shades of Green Lusture - Subvitreous Hardness - 6.5 – 7 Specific gra. - 3.3 – 3.35 Mode of occurrence - It is a rare pyroxene which can occur with albite in some regional metamorphic schists, especially glaucophane. Uses -Jadeite is an ornamental stone constituting one variety of Jade. 24
- 25. Composition - LiAlSi2O6 Crystal sys. - M0n0clinc Form - Usually massive Cleavage - Perfect in two directions with parting Colour - white, grey, lilac, green, blue, pink Lusture - Vitreous , Pearly Hardness - 6.5 – 7 Specific gra. - 3.1-3.3 Mode of occurrence - It is a rare mineral occuring, often as large crystals, in lithium rich, acid pegmatites, where it is associated quartz ,lepidolite ,beryl. Uses - Gemstone & One of the most important source of lithium mineral . 25
- 26. Pyroxenoids 26
- 27. Compo. - CaSiO3 Crystal sys. -Triclinic Form - Crystals are rare , Usually Massive, lamellar, bladed . Cleavage - Perfect Colour -White, gray-white, light green Lusture -Vitreous, Pearly Hardness - 4.5 – 5 Specific gra. - 2.86 – 2.9 Mode of occurrence - It is a product of high grade thermal metamorphism of impure limestone . Uses -Wollastonite is used primarily in ceramics, friction products (brakes and clutches), metalmaking, paint filler, and plastics. 27
- 28. Enstatite It is associated with olivine, diopside and spinel, which are main constituent of ultrabasic and ultramafic rocks. Enstatite phenocrysts also present in olivine tholeiites and tholeiitic andesite. Ferrosillite It is associated with fayalite, hedenbergite, grunerite alamandine and spessartine garnet in eulysite a regionally metamorphosed iron rich sediment. 28
- 29. Diopside – Hedenbergite Diopside and hedenbergite are typical minerals of many metamorphic rocks. Diopside also occurs in the more strongly alkaline rocks (e.g. In the potassium rich lavas ) Hedenbergite is a constituent of pulaskite , foyaite and quartz bearing syenites in which it is usually associated with fayalite. 29
- 30. Augite Augite is the constitute of many hypabyssal rock from picrite to ferrod0lerite. It is an common pyroxene of basic lavas and occurs in members of both tholeiitic and olivine alkali basalt suites. Pigeonite Pigeoniote is particularly characteristic constituent of dacites and andesites In some andesites pigeonite phenocrysts coexist with augite. 30
- 31. Aegirine Aegirine and aegirine-augite are pre eminently the products of the crystallization of alkaline magmas,and many peralkaline rocks ( Na2O + K2O > Al2O3) consist essentially of aegirine pyroxene. Aegirine also occurs in some quartzose rocks and in granulites. 31
- 32. Jadeite Jadeite and jaeditic pyroxenes are relatively common constituents in the metagreywackes and related rocks of regional metamorphic belts. It is also coexist with quartz in the greywackes with omphacites or acmitic pyroxenes in the metabasalts. 32
- 33. Spodumene It is a lithium rich granitic pegmatite . Common associates include quartz, albite, lepidolite and beryl. Wollastonite It is a common mineral of metamorphosed limestone. It also occurs in some alkaline igneous rocks. And in regionally metamorphosed rocks wollastonite may occur in granulite and amphibolite facies. 33
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- 35. Thank you 35