The pyroxene group of minerals03

1. THE PYROXENE GROUP OF MINERALS

3. The Pyroxene Group

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

7. Silica tetrahedrons

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
HedenbergiteCa 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
EnstatiteMg Si O3
FerrosiliteFeSiO3
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
Ferrohypersthene50-70
Eulite 70-90
Orthoferrosilite90-100

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