Pyroxene Group in Geology: Composition and Significance
Feldspar,
Feldspathoid and
Quartz
group
Introduction
Silicate
structure
of
Pyroxene
group
Classification
of
Pyroxene
group
Orthorhombic
Pyroxenes
Monoclinic
Pyroxenes
Pyroxenoids
Paragenesis
References
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
Pyroxenes
have
a
basic
structural
unit
consisting
of
linked
SiO
4
tetrahedra
that
each
share
2
of
their
oxygens
in
such
a
way
as
to
build
long
chains
of
SiO
4
.
The
basic
structural
group
is
thus
Si
2
O
6
with.
Pyroxenes
have
a
general
structural
formula
XYZ
2
O
6
wher
e
,
X
=
N
a
+
,
Ca
2
+
,
M
n
2
+
,
F
e
2
+
,
o
r
M
g
2+
fil
li
n
g
o
c
tah
edral
si
tes
Y
=
Mn
2+
,
Fe
2+
,
Mg
2+
,
Al
3+
,
Cr
3+
,
or
Ti
4+
filling
smaller octahedral
sites
Z
=
Si
4+
or
Al
3+
in tetrahedral
coordination.
4
5
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
Pyroxene
silicate
structure
7
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
Orthopyroxenes
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
(MgSiO
3
)
to
pure
ferrous iron
silicate
(FeSiO
3
).
Cleavage
Colour
Lusture
Hardness
Specific
gravity
Mode
of
occurrence
Uses
massive
&
lamellar
-
Two
sets
of
cleavage
planes
which intersect
at
90°
-
Grey,
green,
brown,
yellow,
Dark
green
-
Vitreous,
pearly
-
6
-3.1
to
3.3
-
As
a
common
constituent
of
igneous
&
metamorphic
rock.
-
As
a
Gemstone
11
Composition
Crystal
system
12
Common
form
Cleavage
C
o
lo
u
r
-
MgFeSiO
3
–
Orthorhombic
–
Prismatic
crystals
are
rare
usually
massive
or
foliaceous
-Three
sets
of
cleavage
in
transverse
section
-
Commonly
green,
olive
green
to
greenish
black
-
Vitreous,
pearly
-
6
-
3.1
to
3.3
Lusture
Hardness
Specific
gravity
Mode
of
occurrence
–
As
a
common
constitute
of
volcanic
igneous rock
like
andesite
and
trachytes
.
Uses
-
As
a
gemstone
Uses
-Jadeite
is
an
ornamental stone
constituting
one
variety of
Jade.
24
Colour
Lusture
Hardness
Specific
gra.
Mode
of
occurrence
Uses
with
parting
-
white,
grey, lilac,
green,
blue,
pink
-
Vitreous
,
Pearly
-
6.5
–
7
-
3.1-3.3
-
It
is
a
rare
mineral
occuring,
often
as large
crystals,
in
lithium
rich,
acid
pegmatites,
where
it is
associated
quartz ,lepidolite
,beryl.
-
Gemstone
&
One
of
the
most
important
source
of lithium
mineral
.
Thank
you
15
Pyroxenes are vital rock-forming minerals found in various types of igneous rocks and metamorphic conditions. They consist of linked SiO4 tetrahedra, forming structural chains with specific chemical compositions. The orthorhombic and monoclinic pyroxenes play essential roles in geology, demonstrating distinct crystal systems and properties within the inosilicate subdivision. This overview explores the classification, structural characteristics, and significance of pyroxenes in geological processes.
Download Presentation
Please find below an Image/Link to download the presentation.
The content on the website is provided AS IS for your information and personal use only. It may not be sold, licensed, or shared on other websites without obtaining consent from the author.If you encounter any issues during the download, it is possible that the publisher has removed the file from their server.
You are allowed to download the files provided on this website for personal or commercial use, subject to the condition that they are used lawfully. All files are the property of their respective owners.
The content on the website is provided AS IS for your information and personal use only. It may not be sold, licensed, or shared on other websites without obtaining consent from the author.
E N D
Presentation Transcript
Feldspar, Feldspathoid and Quartz group Dr. A.V.Tejankar Professor & Head Dept. of Geology Deogiri College, Aurangabad
Introduction Silicate structure of Pyroxenegroup Classification of Pyroxenegroup Orthorhombic Pyroxenes Monoclinic Pyroxenes Pyroxenoids Paragenesis References
3 Pyroxenes are the most important group of rockforming ferromagnesiam silicates , and occur as stable phases in every type of igneousrock. They are also found in many rocks of widely different compositions formed under the conditions of both thermal and regionalmetamorphism. The name pyroxeneis derived fromtheGreekpyro, meaning fire, and xenos, meaning "stranger", and was given by Ha y to the greenish crystals found in many lavas which he considered tohave been accidentally included there.
4 Pyroxenes have a basic structuralunit consisting of linked SiO4tetrahedra 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 structuralformula XYZ2O6 where,X = Na+,Ca2+, Mn2+, Fe2+, orMg2+filling octahedral sites Y = Mn2+, Fe2+, Mg2+ , Al3+, Cr3+, or Ti4+ filling smaller octahedral sites Z= Si4+ or Al3+ in tetrahedral coordination.
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
7 Pyroxene silicate structure
8 The pyroxenes may be divided forour purpose into the groups given below ; varieties based mainly on physical characters are considered under their appropriate chemicalgroups. Orthorhombic Pyroxenes ( orthopyroxenes) Monoclinic Pyroxenes ( clinopyroxenes) I. II.
The Pyroxenes which crystallizes in orthorhombic crystal system are known asorthopyroxenes. 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).
11 Composition Crystal system Common form - MgSiO3 Orthorhombic Prismatic crystals massive &lamellar - Two sets of cleavageplanes which intersect at90 - Grey, green, brown,yellow, Dark green -Vitreous, pearly - 6 -3.1 to3.3 - As a common constituent of igneous & metamorphicrock. -As aGemstone Cleavage Colour Lusture Hardness Specific gravity Mode ofoccurrence Uses
12 Composition Crystalsystem - MgFeSiO3 Orthorhombic Prismatic crystals are rare usually massive orfoliaceous -Three sets of cleavagein transverse section -Commonly green,olive green to greenishblack - Vitreous, pearly - 6 - 3.1 to3.3 Commonform Cleavage Colour Lusture Hardness Specificgravity Modeofoccurrence As a common constitute of volcanic igneous rock like andesite andtrachytes. Uses -As agemstone
Composition Crystal sys. Form - NaAlSi2O6 - M0n0clinc -Prismatic crystals Usuallymassive - Prismatic at90 -Shades ofGreen -Subvitreous - 6.5 7 - 3.3 3.35 Cleavage Colour Lusture Hardness Specific gra. Mode ofoccurrence - It is a rarepyroxenewhich can occur in some regional metamorphic schists, especially glaucophane. -Jadeite is anornamental stone constituting one variety ofJade. Uses 24
Composition Crystal sys. Form Cleavage - LiAlSi2O6 - M0n0clinc - Usuallymassive -Perfect in two directions with parting - white, grey, lilac, green,blue, pink - Vitreous ,Pearly - 6.5 7 -3.1-3.3 -It is a rare mineral occuring, often as large crystals, in lithium rich, acid pegmatites, where it is associated quartz ,lepidolite,beryl. -Gemstone &One ofthemost important source of lithium mineral . Colour Lusture Hardness Specific gra. Mode ofoccurrence Uses
Thank you 15
