1. Use of the petrographic microscope
Optical Mineralogy
Use of the petrographic microscope

3. Pyroxenes

4. Not only pyroxenes

5. Olivine

6. Olivine

7. Olivine

8. Clinopyroxenes (monoclinic) & Orthopyroxenes (orthorhombic)

9. Clinopyroxenes (monoclinic)
Aegirine (Sodium Iron Silicate)
Augite (Calcium Sodium Magnesium Iron Aluminium Silicate)
Clinoenstatit (Magnesium Silicate)
Diopside (Calcium Magnesium Silicate, CaMgSi2O6)
Esseneite (Calcium Iron Aluminium Silicate)
Hedenbergite (Calcium Iron Silicate)
Jadeite (Sodium Aluminium Silicate)
Johannsenite (Calcium Manganese Silicate)
Kanoite (Manganese Magnesium Silicate)
Kosmochlor (Sodium Chromium Silicate)
Namansilite (Sodium Manganese Silicate)
Natalyite (Sodium Vanadium Chromium Silicate)
Omphacite (Calcium Sodium Magnesium Iron Aluminium Silicate)
Petedunnite (Calcium Zinc Manganese Iron Magnesium Silicate)
Pigeonite (Calcium Magnesium Iron Silicate)
Spodumene (Lithium Aluminium Silicate)
Jervisite (Sodium Calcium Iron Scandium Magnesium Silicate)

10. Augite (Calcium Sodium Magnesium Iron Aluminium Silicate)
Aegirine (Sodium Iron Silicate)
Augite (Calcium Sodium Magnesium Iron Aluminium Silicate)
Clinoenstatit (Magnesium Silicate)
Diopside (Calcium Magnesium Silicate, CaMgSi2O6)
Hedenbergite (Calcium Iron Silicate)
Pigeonite (Calcium Magnesium Iron Silicate)

11. Augite (Calcium Sodium Magnesium Iron Aluminium Silicate)
Aegirine (Sodium Iron Silicate)
Augite (Calcium Sodium Magnesium Iron Aluminium Silicate)
Clinoenstatit (Magnesium Silicate)
Diopside (Calcium Magnesium Silicate, CaMgSi2O6)
Hedenbergite (Calcium Iron Silicate)
Pigeonite (Calcium Magnesium Iron Silicate)

12. Orthopyroxenes (orthorhombic) Hypersthene (Magnesium Iron Silicate) Donpeacorite, (Mg Mn)MgSi2O6 Enstatite, Mg2Si2O6 Ferrosilite, Fe2Si2O6 Nchwaningite (Hydrated Manganese Silicate) Bronzite ………(Bastite)

13. Orthopyroxenes (orthorhombic) Hypersthene, (Magnesium Iron Silicate) Enstatite, ( Mg2Si2O6 )

14. A few properties, and then some review…
Cleavage – number and orientation of cleavage
planes
Twinning – type of twinning, orientation
Extinction angle – parallel or inclined? Angle?
Habit – characteristic form of mineral

15. Cleavage
Most easily observed in PPL (upper polarizer out), but visible in XN as well
No cleavages: quartz, olivine
1 good cleavage: micas
2 good cleavages: pyroxenes, amphiboles

16. Cleavage
2 cleavages intersecting
at ~90° pyroxene

17. Twinning
Presence and style of twinning can be diagnostic
Twins are usually most obvious in XN (upper polarizer in)

18. Twinning - some examples
Clinopyroxene (augite)
Simple twin on {100}

19. Extinction angle
Extinction behavior is a function of the relationship between indicatrix orientation and crystallographic orientation
inclined extinction
parallel extinction

20. Extinction angle – parallel extinction
orthopyroxene XN
PPL

21. Extinction angle - inclined extinction
Clino Pyroxene inclined extinction
(and extinction angle helps to identify them)
extinction angle
clinopyroxene

22. Enlarged pyroxene
pyroxene
PPL
XPL
Pyroxene Well-formed crystal seen here with 2 cleavages at 90o: Brightly coloured under XPL

23. Review – techniques for identifying unknown minerals
Start in PPL:
Color/pleochroism
Relief
Cleavages
Habit
Then go to XPL:
Birefringence
Twinning
Extinction angle
Uniaxial or biaxial?
2V if biaxial
Positive or negative?

24. (a) Pyroxene (b) Amphibole. (c) Black biotite (mica) .

26. This first photograph shows a pyroxene crystal with cleavage aligned E-W along the crosshairs. The second photograph shows the same crystal in an extinction position. This shows inclined extinction

27. Pyroxene & Amphibole

28. Muscovite & Biotite

29. Augite is the most common pyroxene, with the formula (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6. It is the typical pyroxene in mafic igneous rocks.
Augite is usually black, with stubby crystals. It is a common primary mineral in basalt, gabbro and peridotite and a metamorphic mineral in gneiss and schist.

30. Diopside is a light-green mineral with the formula CaMgSi2O6 typically found in contact-metamorphosed limestone. It forms a series with hedenbergite, CaFeSi2O6.
Calcium Pyroxene

31. Aegirine is a green or brown pyroxene with the formula NaFe3+Si2O6
Aegirine is a green or brown pyroxene with the formula NaFe3+Si2O6. It is no longer called acmite or aegirite.
(Sodium Pyx)

32. Enstatite is a common greenish pyroxene with the formula MgSiO3
Enstatite is a common greenish pyroxene with the formula MgSiO3. With increasing iron content it turns dark brown; its iron version is ferrosilite.
Magnesium Pyroxene

33. Bronzite - Dark brown or greenish-brown, opaque variety of Enstatie or Hypersthene with a submetalic luster . Bronzite is formed through weathering of normal Enstatite or Hypersthene.
Hypersthene

34. Bronzite - Dark brown or greenish-brown, variety of Enstatie or Hypersthene with a submetalic luster. Bronzite is formed through weathering of normal Enstatite or Hypersthene Hypersthene

39. Mineralogical composition of the principal mantle peridotites
Minerals
Peridotites
Olivine
Enstatite
Diopside
Aluminum Minerals
LHERZOLITE
60-70%
20%
5-I0%
Plagioclase<30km
30km< Spinelle <75km
Garnet>75km
HARZBURGITE
70-80%
0-5%
Spinelle 5%
DUNITE
95%
1-2
0-0.5
(Chromite) 5%

42. Calcite

44. You might have seen a pattern of colored light formed by interference between white light being reflected from the surface of a thin film of diesel fuel on the surface of water, and the diesel-water interface.