PYROXENE

1. Pyroxene group of minerals
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2.  Introduction
 Silicate structure of Pyroxene group
 Classification of Pyroxene group
 Orthorhombic Pyroxenes
 Monoclinic Pyroxenes
 Pyroxenoids
 Paragenesis
 References
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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.
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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.
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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
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7. Pyroxene silicate structure
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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 )
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9. Orthopyroxenes
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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).
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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
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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
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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
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14. Monoclinic Pyroxenes
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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.
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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.
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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
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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.
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22. C. Alkali – Pyroxenes
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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
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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 .
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26. Pyroxenoids
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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34.  DEER W.A., HOWIE R.A. & ZUSSMAN J. An
Introduction to the Rock Forming Minerals,2nd
edition,Addisson wesley longman limited, 1992
( page no. 143 to 203 )
 GRIBBLE C.D. ,Rutleys Element Of Mineralogy 27th
edition,C.B.S. Publishers 2005 ( page no. 374 to 384 )
 READ H. H. ,Rutleys Element Of Mineralogy 25th
edition,Surjeet publications( page no. 335 to 344 )
 https://geology.com/ (as accessed on 1/10/2019)
 https://www.minerals.net/ (as accessed on 1/10/2019)
 www.alexstrekeisen.it (as accessed on 1/10/2019)
 www.mindat.org (as accessed on 1/10/2019)
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35. Thank you
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