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Source of course material Dr. Olaf Medenbach, Ruhr-Universit ä t Bochum Optical microscopy of...
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![Page 1: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/1.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Compact Course
Microscopy of rock-forming Minerals
Part 7: Garnet, Andalusite, Sillimanite, Kyanite, Staurolite, Chloritoid, Corundum, Rutile, Spinel, Limonite, Opaque Ores, Artefacts, Miscellaneous
![Page 2: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/2.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
GarnetFormula :(Mg,Fe,Mn,Ca)3(Al,Fe,Cr)2[SiO4]3
Symmetriy : cubic
n : 1,71 – 2,0
n : -
2V : -
max. I. F. (30μm) : -
Observations:
Isotropic, high relief, often idiomorphic, colour rose to brownish-red. Can only be confuses with spinel. Difference are in shape and chagrins.
Spinel crystallized in octahedra (shapes with 3, 4 or max. 6 corners. Garnet shows rounded shapes.
![Page 3: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/3.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Garnet
0,1 mm
Observations:
idiomorophic garnet crystals next to amphibole, included in quartz.
NoteNote: : very small crystals can appear to be non-isotropic due to the underlying quartz.
perfect rhombic-dodekaeder
![Page 4: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/4.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
GarnetObservations:
Poicilitic growth of garnet, including many other crystals gives a sieve-like texture.
1 mm
![Page 5: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/5.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
GarnetObservations:
Kelyphytic reaction rim around garnet.
1 mm
![Page 6: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/6.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
GarnetObservations:
.
1 mm
Observations:
• Deformation
• Rotation of garnet
• inclusion trails
• Such rotated garnets are called: „snow ball garnets“. They grow during the deformation of the rock.
![Page 7: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/7.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
GarnetObservations:
.
1 mm
Observations:
• Deformation
• Rotation of garnet
• inclusion trails
• Such rotated garnets are called: „snow ball garnets“. They grow during the deformation of the rock.
![Page 8: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/8.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
GarnetObservations:
Atoll-shaped garnet due to partial replacement of a particular growth zone, which may be instable for its distinct compositin.
1 mm
![Page 9: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/9.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
AndalusiteFormula : Al[5]Al[6][O|SiO4]
Symmetriy : orthorhombic
n : 1,629 – 1,640
n : 0,009 – 0,011
2Vx : 83° - 85°
max. I. F. (30μm) : white I. order
Observations:
Generally prismatic, ceavage following {110} at 90°, sometimes pleochroic. Chiastolite with inclusions forming a typical 90° cross. In metamorphic rocks at relatively low P and T, contact metamorphic slates.
![Page 10: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/10.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
AndalusiteObservations:
Compositional zonation in andalusite with rose-to clolourless pleochroism in the core. Note claevage following {110} at 90° in sections with c
c vertical
c horizontal
1 mm
![Page 11: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/11.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Andalusite
1 mm
![Page 12: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/12.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Andalusite
1 mm
Observations:
Large porphyroblasts with poikilitic texture.
![Page 13: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/13.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Andalusite
1 mm
Observations:
Chiastolite
![Page 14: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/14.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
SillimaniteFormula : Al[4]Al[6][O|SiO4]
Symmetry : orthorhombic
n : 1,657 – 1,682
n : 0,02 – 0,022
2Vz : 21° - 30°
max. I. F. (30μm) : white I. order
Observations:
Typically long-prismatic to fibrous crystals. Larger crystals show one direction of cleavage{010}
Optical character in elongation is positive (important because small crystals will not give interference images of axes).
![Page 15: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/15.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
SillimaniteObservations:
Zoned Sillimanite with rose-colourless pleochroism in the core. Note cleavage along {110} at 90° in sections with vertical c.
c vertical
c horizontal
1 mm
![Page 16: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/16.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Sillimanite
0,5 mm
![Page 17: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/17.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Sillimanite, Fibrolite, orientiented inclusions in cordierite
0,5 mm
![Page 18: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/18.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Sillimanite, Fibrolite, Detail
0,2 mm
Observations:
• oriented parallel to thin section plane (elongated sections, c horizontal)
• oriented vertical to thin section plane (c vertical)
![Page 19: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/19.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
KyaniteFormula : Al[6]Al[6][O|SiO4]
Symmetry : triclinic
n : 1,710 – 1,729
n : 0,016 – 0,017
2Vz : 82°
max. I. F. (30μm) : Orange I. order
Observations:
Due to perfect cleavage and rigid mechanical behaviour crystals in thin sections often show break-outs.
![Page 20: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/20.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Kyanite
1 mm
![Page 21: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/21.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Kyanite
Observations:
Twin with both crystals almost in identical optical orientation, note the slight angle between cleavage planes of the twins.
1 mm
Trace of twin plane
Trace of twin plane
![Page 22: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/22.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Kyanite
0,5 mm
![Page 23: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/23.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
KyaniteObservations:
There are three main components, all with high refractive index. Try to distinguish..:
• Garnet: isotropic character
• Jadeite: retrograde reaction rims
• Kyanite: no reaction rims
1 mm
![Page 24: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/24.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
StauroliteFormula : 2FeO•AlOOH•4Al2[O|SiO4]
Symmetry : monoclinic
n : 1,739 – 1,762
n : 0,013 – 0,015
2Vz : 79° - 90°
max. I. F. (30μm) : Orange I. order
Observations:
High refractive index, low birefringence, yellow to brown colour, twins often observed.
![Page 25: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/25.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Staurolite
1 mm
Observations:
Idiomorphic, poikilitic crystals as porphyroblasts in a contact metamorphic shist, together with large crystals of andalusite.
![Page 26: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/26.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Staurolite Nr. 63
1 mm
Observations:
Idiomorphic, poikilitic crystals as porphyroblasts in a contact metamorphic shist, together with large crystals of andalusite.
![Page 27: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/27.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Staurolite Nr. 57Observations:
Idiomorphic porphyroblasts growing over pre-existing schistosity texture.
1 mm
![Page 28: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/28.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Staurolite Nr. 57
1 mm
Observations:
Idiomorphic porphyroblasts growing over pre-existing schistosity texture.
![Page 29: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/29.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Staurolite Nr. 38
0,5 mm
Observations:
Andalusite-cystals with inclusions of staurolite.
Staurolite
![Page 30: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/30.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Chloritoide Formula : (Fe,Mg,Mn)Al2[(OH)2|O|SiO4]
Symmetry : monoclinic and triclinic
n : 1,682 – 1,740
n : 0,010 – 0,012
2Vz : 36° - 70°
max. I. F. (30μm) : white I. order
Observations:
High refractive index, low birefringence, blue-green colour, twins often observed. Anomalous blueish interference colours near position of extinction.
![Page 31: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/31.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Chloritoide
0,5 mm
Observations:
Chloritoide porphyroblast overgrew older schistisity.
![Page 32: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/32.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Chloritoid
1 mm
Observations:
Strong pleochrosim in Fe-rich chloritoide, polysynthetic twins.
Direction of polarizing planeDirection of polarizing plane
![Page 33: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/33.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
CorundumFormula : Al2O3
Symmetry : trigonal
n : 1,759 – 1,772
n : 0,008 – 0,009
2V : -
max. I. F. (30μm) : white I.order
Observations:
Easy to recognize: high refractive index similar to garnets, low birefringence similar to quartz, uniaxial.
Rose to blue-coloured.
Typical fractures parallel {1011}
![Page 34: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/34.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
CorundumObservations:
Typical fractures parallel{1011}are not a cleavage ! as indicated by effects of anisotropy on these planes.
1 mm
![Page 35: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/35.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
CorundumObservations:
Fractures parallel {1011}.
1 mm
![Page 36: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/36.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Corundum
Observations:
• c vertical
• c horizontal
with chloritoide and opaque ore
0,5 mm
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Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
RutileFormula : TiO2
Symmetry : tetragonal
n : 2,6 – 2,9
n : 0,3 !!!!!
2V : -
max. I. F. (30μm) : white I. order
Observations:
Mineral with the highes refractive index and highest birefringence. Always intesively yellow to brown colours, weak pleochroism
ne>no. Interference image of axis difficult to
see due to high chagrins. Cleavage {110} (90°). Twins.
![Page 38: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/38.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Rutile
Observations:
• c vertical
• cleavage at 90°!
0,5 mm
![Page 39: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/39.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
SpinelFormula : (Fe,Mg,Mn)(Al,Fe3+,Cr)2O4
Symmetry : cubic
n : 1,718 – 2,05
n : -
2V : -
max. I. F. (30μm) : -
Observations:
Isotropic, high relief, very similar to garnets. Spinels, however, crystallize in octahedral shape and thus cyrstals have few faces (3, 4 to max. faces).
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Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Spinel
1 mm
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Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
LimoniteFormula : FeOOH
Symmetry : rhombic
n : ~ 2 – 2,5
n : 0,6 0,6 (L.), 0,08-0,14(G.)
2V :
max. I. F. (30μm) : very high, white
Observations:
Mixture of goethite and lepidokrokit, often rhythmically intergrown. Results from alteration and oxidation of Fe-bearing sulphides (pyrite, chalkopyrite, etc.). „Rust“ that is a finely dispered brown pigment in weathered rocks.
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Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Limonite
0,2 mm
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Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Research microscope with transmitted and reflected light.
Opaque minerals(Fe-Ti oxides, sulphides, graphite)
To investigate opaque minerals, reflected light microscopes are needed.
Only in rare cases, from crystal shapes and alteration products, some information on this group of minerals can be gained even with a transmitted light microscope. Examples follow.
.
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Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Reflected light microscope
to oculars and to oculars and observerobserver
from light from light sourcesource
optical beam optical beam splittersplitter
samplesample
illuminatorilluminator
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Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Graphite
0,5 mm
Observations:
Elongated plates, often deformed and bent and kinked, splayed margins like staked paper (similar to micas)
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Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Magnetite
0,2 mm
Observations:
With ilmenite most abundant Fe-Ti Oxide and opaque minerals in igneous rocks. Crystal shape : octahedra -> isometric cross sections, mostle triangular to cubic, more rarels hexagonal sections.
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Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Magnetite
1 mm
Observations:
Isometriis cross sectionss, examples of fast-frown crystal with sceletal shape.
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Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Chromite - Magnetite
0,5 mm
Observations:
Zoned crystal from solid solution series between magnesiochromite (MgCr2O4) and chromite (FeCr2O4). Magnesiochromite is brown translucent. Typical for mafic and ultramafic igneous rocks.
![Page 49: 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.](https://reader038.fdocuments.in/reader038/viewer/2022103006/56649ef55503460f94c089e8/html5/thumbnails/49.jpg)
Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Ilmenite
0,5 mm
Observations:
• elongated platy crystals: Ilmenite
• 6-sided cross sections : ilmentige with c vertical of a cubic opaque mineral (magnetite)
MagnetiteMagnetite
IlmeniteIlmenite
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Source of course material Dr. Olaf Medenbach, Ruhr-Universität Bochum
Optical microscopy of rock-forming minerals, G. Wörner, USTC Hefei
Pyrite
0,2 mm
Observations:
Fe-sulphide altered to limonite at the rim (pyrite or chalkopyrite).