13Orthopyroxenes (orthorhombic) Hypersthene, (Magnesium Iron Silicate) Enstatite, ( Mg2Si2O6 )
14A few properties, and then some review… Cleavage – number and orientation of cleavageplanesTwinning – type of twinning, orientationExtinction angle – parallel or inclined? Angle?Habit – characteristic form of mineral
15CleavageMost easily observed in PPL (upper polarizer out), but visible in XN as wellNo cleavages: quartz, olivine1 good cleavage: micas2 good cleavages: pyroxenes, amphiboles
22Enlarged pyroxenepyroxenePPLXPLPyroxene Well-formed crystal seen here with 2 cleavages at 90o: Brightly coloured under XPL
23Review – techniques for identifying unknown minerals Start in PPL:Color/pleochroismReliefCleavagesHabitThen go to XPL:BirefringenceTwinningExtinction angleUniaxial or biaxial?2V if biaxialPositive or negative?
24(a) Pyroxene (b) Amphibole. (c) Black biotite (mica) .
29Augite 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.
30Diopside is a light-green mineral with the formula CaMgSi2O6 typically found in contact-metamorphosed limestone. It forms a series with hedenbergite, CaFeSi2O6.Calcium Pyroxene
31Aegirine 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)
32Enstatite 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
33Bronzite - 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
34Bronzite - 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
39Mineralogical composition of the principal mantle peridotites MineralsPeridotitesOlivineEnstatiteDiopsideAluminum MineralsLHERZOLITE60-70%20%5-I0%Plagioclase<30km30km< Spinelle <75kmGarnet>75kmHARZBURGITE70-80%0-5%Spinelle5%DUNITE95%1-20-0.5(Chromite) 5%
44You 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.