Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei Compact Course Microscopy of rock-forming Minerals Part 4: amphiboles and pyroxenes

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei amphibole Formula: very complex group of chain silicates Symmetry: rhombic / monoclinic n: 1,6 – 1,8  n: 0,01 – 0,03 2V: highly variable max. I. F. (30μm) : I. – II. Order Observations: In sections with vertical c-axis typical cleavage angles {110} of 120°. Strongly coloured varieties are pleochroic Orthoamphibole green and brown amphiboles" "blue amphiboles" “colourless amphiboles"

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei amphibole, orientation with vertical c ~(001) 0,5 mm Direction of polarizing plane b a‘ beige olive green Note: only in direction of n x and n z you will see the exact pleochroic colours, all other directions will show mixed colours!

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei amphibole, elongated with c parallel thin section ~(100) plane 0,5 mm Direction of polarizing plane c b olive green blue- green

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei Nr. 2 0,5 mm amphibole, section parallel (010) Position of extinction not completely black because of disperion Orientientation of indicatrix Extinction angle Direction of polarizing plane c a beige blue-green

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei b a‘ beige olive green c b blue green c a beige blue green blue green olive green beige amphibole, Schematics of pleochroism Note: determination of extinction angle ONLY possible along (010) with pleochroism blue green to beige and maximum interference colours)! ZcZcZcZc

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei amphibole 0,3 mm Direction of polarizing plane

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei amphibole 0,5 mm Observations: Paragenesis: Amphibole Epidote Chlorite

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei amphibole Nr mm Observations: Retrograde Eclogite Garnet Titanite

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei amphibole Nr. 26 0,5 mm Observations: Alkali-Amphibole, extremely anomalous interference colours, strong zonation. Turbid, elongated crystals are ternary feldspars with perthitic exsolutions. Green: Aegirine.

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei amphibole 0,3 mm Direction of polarizing plane

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei b a‘ beige violett c b ultramarine c a beige ultramarine violett beige amphibole, Pleochrosim of blue amphiboles Note: determination of extinction angle ONLY possible along (010) with pleochroism ultramarine- beige ! ZcZcZcZc

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei amphibole 0,5 mm Observations: c vertical c elongated ~(010) c elongated ~(100)l'(-)l'(+) Note: It is possible to determine the type of blue amphibole (glaucophane, crossite or magnesio-riebeckite) by determining the position of the indicatrix.

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei amphibole 1 mm Observations: Blue amphibole next tp Garnet Epidote Titanite

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei Orthoamphibole 0,5 mm Observations: Orthoamphibole with faint leochroisms and exsolutions. Orientation c vertical. Note: Note: finding appropriate elongated cross sections (c parallel thin section plane) you can determine the extinction angle and thus the type of amphibole.

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei Pyroxene Formula: (Mg,Fe,Ca)[Si 2 O 6 ] Jadeite NaAl[Si 2 O 6 ], Aegirine NaFe 3+ [Si 2 O 6 ]) Symmetry: orthorhombic/ monoclinic n: 1,65 – 1,80 (1,84 for Na-pyroxenes)  n: 0,01 – 0,03 (0,06) 2V: highly variable max. I. F. (30μm) : I. – III. Order Observations: In cross sections with c vertical typical shape and 90° cleavage along{110}. Orthopyroxene Diopside-Hedenbergite Augite Titanaugite Aegirine-Augite 2V EnFsx 90°

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei Pyroxene 0,5 mm Observations: Idiomorpic crystals in fine- grained matrix c is vertical c is horizintalNote: Many andesites have two types of pyroxene : Opx: normal extinction // c, low interference colour. Cpx: extinction at angle with c, high interference colours.

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei Orthopyroxene (Bronzite) 1 mm Observations: Orthopyroxenite. Hypidiomorphic to idiomorphic Opx (Bronzite) with exsolutions of cpx. c is vertical c is horizontal 2V of Opx depends on composition: 2V EnFsx 90°

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei Orthopyroxene (Hypersthene) 1 mm Observations: Hypersthene shows very nice pleochroism! Note: Note: you can work out the schematics of pleochroism Direction of polarizing plane

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei Orthopyroxene (Hypersthen) 1 mm Observations: c is vertical Direction of polarizing plane

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei Clinopyroxene 1 mm Observations: Xenomorphic crystals intergrown with plagioclase, some amphibole and Fe- oxide.

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei 0,5 mm Observations: Detail in sections c vertical. Clinopyroxene Nr. 65

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei Observations: Turbid cpx, altered plagioclase and olivines with alteration rinds. Clinopyroxene 1 mm

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei Two distinct pyroxenes 1 mm Observations: cpx, opx and plagioclase. Alteration in Opx at grain boundaries and along cleavage planes. opx cpx, c is vertical opx: normal extinction //c, low interference colour. cpx: extintion not // c, High interference colour During alteration, opx will be affected more rapidly and severely compared to cpx, which often may aid identification.

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei 1 mm Two distinct pyroxenes Observations: cpx, opx and plagioclase. Opx with higher relief and alteration. opx cpx cpx: extinction not // c, High interference colour During alteration, opx will be affected more rapidly and severely compared to cpx, which often may aid identification.

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei 1 mm Two distinct pyroxenes Nr. 61 Observations: cpx and opx. Opx with higher relief. opx cpx: extinction not // c, High interference colour During alteration, opx will be affected more rapidly and severely compared to cpx, which often may aid identification.

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei 1 mm Aegirine, NaFe 3+ [Si 2 O 6 ] Nr. 26 Observations: Sperolithic aggregates, sections //c.

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei 0,1 mm Observations: Impressive pleochroism, perfectly developed clevage at 90° in sections vertical c. Note: Note: You can work out the scheme of pleochroism Aegirine, NaFe 3+ [Si 2 O 6 ] Direction of polarizing plane Typical for alkaline volcanic and plutonic rocks

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei 0,5 mm Aegirine, NaFe 3+ [Si 2 O 6 ] Observations: Aegirine as phenocryst. Small prisms in fine-grained matrix. Aegirine c vertical Titanite Typical for alkaline volcanic and plutonic rocks

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei 1 mm Jadeite, NaAl[Si 2 O 6 ] Observations: Jadeite, high-pressure clinopyroxene, retrogression to albite following this reaction : NaAl[Si 2 O 6 ] + SiO 2 = NaAl[Si 3 O 8 ] Garnet Jadeite c vertical retrograde replacement along grain boundaries and cleavage planes

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei 1 mm Omphacite Observations: Omphacite replaces plagioclase at high pressures (in eclogites). Intermediate member of solid solution series between Jadeite NaAl[Si 2 O 6 ] and Diopside CaMg[Si 2 O 6 ]. Omphacite c is vertical Garnet

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei Observations: Hour glass structure Hour glass structure: Different segments of crystals have different compositions and thus different optical properties. When crystals grow, elemental partitioning depends on, and is different for, distinct crystallographic growth planes. Sectors are different in: pleochroism extinction angle anomalous interference colours near extinction 1 mm Titanian Augite

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei 1 mm Titanian Augite Observations: Leucite Vesicle Vesicle filled with epoxy and air bubble. Birefringence in resin due to strain.

Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of rock-forming minerals, G. W ö rner, USTC Hefei 1 mm Titanian Augite Observations: Titanian augite: large phenocrysts in finer-grained matrix. Smaller Ti-augite have highly anomalous interference colours.