1 / 50

Compact Course Microscopy of rock-forming Minerals

Compact Course Microscopy of rock-forming Minerals Part 7: Garnet, Andalusite, Sillimanite, Kyanite , Staurolite, Chloritoid, Corundum, Rutile, Spinel, Limonite, Opaque Ores, Artefacts, Miscellaneous. Garnet Formula :(Mg,Fe,Mn,Ca) 3 (Al,Fe,Cr) 2 [SiO 4 ] 3 Symmetriy : cubic n : 1,71 – 2,0

red
Download Presentation

Compact Course Microscopy of rock-forming Minerals

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Compact Course Microscopy of rock-forming Minerals Part 7: Garnet, Andalusite, Sillimanite, Kyanite, Staurolite, Chloritoid, Corundum, Rutile, Spinel, Limonite, Opaque Ores, Artefacts, Miscellaneous

  2. Garnet Formula :(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.

  3. 0,1 mm Garnet Observations: idiomorophic garnet crystals next to amphibole, included in quartz. Note: very small crystals can appear to be non-isotropic due to the underlying quartz. perfect rhombic- dodekaeder

  4. 1 mm Garnet Observations: Poicilitic growth of garnet, including many other crystals gives a sieve-like texture.

  5. 1 mm Garnet Observations: Kelyphytic reaction rim around garnet.

  6. 1 mm Garnet Observations: . • Observations: • Deformation • Rotation of garnet • inclusion trails • Such rotated garnets are called: „snow ball garnets“. They grow during the deformation of the rock.

  7. 1 mm Garnet Observations: . • Observations: • Deformation • Rotation of garnet • inclusion trails • Such rotated garnets are called: „snow ball garnets“. They grow during the deformation of the rock.

  8. 1 mm Garnet Observations: Atoll-shaped garnet due to partial replacement of a particular growth zone, which may be instable for its distinct compositin.

  9. Andalusite Formula : 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.

  10. 1 mm Andalusite Observations: 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

  11. 1 mm Andalusite

  12. 1 mm Andalusite Observations: Large porphyroblasts with poikilitic texture.

  13. 1 mm Andalusite Observations: Chiastolite

  14. Sillimanite Formula : 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).

  15. 1 mm Sillimanite Observations: Zoned Sillimanite with rose-colourless pleochroism in the core. Note cleavage along {110} at 90° in sections with vertical c. c vertical c horizontal

  16. 0,5 mm Sillimanite

  17. 0,5 mm Sillimanite, Fibrolite, orientiented inclusions in cordierite

  18. Observations: • oriented parallel to thin section plane (elongated sections, c horizontal) • oriented vertical to thin section plane (c vertical) 0,2 mm Sillimanite, Fibrolite, Detail

  19. Kyanite Formula : 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.

  20. 1 mm Kyanite

  21. Trace of twin plane 1 mm Kyanite Observations: Twin with both crystals almost in identicaloptical orientation, note the slight angle between cleavage planes of the twins.

  22. 0,5 mm Kyanite

  23. 1 mm Kyanite • Observations: • There are three main components, all with high refractive index. Try to distinguish..: • Garnet: isotropic character • Jadeite: retrograde reaction rims • Kyanite: no reaction rims

  24. Staurolite Formula : 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.

  25. 1 mm Staurolite Observations: Idiomorphic, poikilitic crystals as porphyroblasts in a contact metamorphic shist, together with large crystals of andalusite.

  26. 1 mm Staurolite Nr. 63 Observations: Idiomorphic, poikilitic crystals as porphyroblasts in a contact metamorphic shist, together with large crystals of andalusite.

  27. 1 mm Staurolite Nr. 57 Observations: Idiomorphic porphyroblasts growing over pre-existing schistosity texture.

  28. 1 mm Staurolite Nr. 57 Observations: Idiomorphic porphyroblasts growing over pre-existing schistosity texture.

  29. 0,5 mm Staurolite Nr. 38 Observations: Andalusite-cystals with inclusions of staurolite. Staurolite

  30. 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.

  31. 0,5 mm Chloritoide Observations: Chloritoide porphyroblast overgrew older schistisity.

  32. Direction of polarizing plane 1 mm Chloritoid Observations: Strong pleochrosim in Fe-rich chloritoide, polysynthetic twins.

  33. Corundum Formula : 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}

  34. Observations: Typical fractures parallel{1011}are not a cleavage ! as indicated by effects of anisotropy on these planes. 1 mm Corundum

  35. Observations: Fractures parallel {1011}. 1 mm Corundum

  36. 0,5 mm Corundum • Observations: • c vertical • c horizontal • with chloritoide and opaque ore

  37. Rutile Formula : 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.

  38. 0,5 mm Rutile • Observations: • c vertical • cleavage at 90°!

  39. Spinel Formula : (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).

  40. 1 mm Spinel

  41. Limonite Formula : FeOOH Symmetry : rhombic n : ~ 2 – 2,5 n : 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.

  42. 0,2 mm Limonite

  43. 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. . Research microscope with transmitted and reflected light.

  44. to oculars and observer illuminator from light source optical beam splitter sample Reflected light microscope

  45. 0,5 mm Graphite Observations: Elongated plates, often deformed and bent and kinked, splayed margins like staked paper (similar to micas)

  46. 0,2 mm Magnetite 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.

  47. 1 mm Magnetite Observations: Isometriis cross sectionss, examples of fast-frown crystal with sceletal shape.

  48. 0,5 mm Chromite - Magnetite Observations: Zoned crystal from solid solution series between magnesiochromite (MgCr2O4) and chromite (FeCr2O4). Magnesiochromite is brown translucent. Typical for mafic and ultramafic igneous rocks.

  49. Ilmenite Magnetite 0,5 mm Ilmenite • Observations: • elongated platy crystals: Ilmenite • 6-sided cross sections : ilmentige with c vertical of a cubic opaque mineral (magnetite)

  50. 0,2 mm Pyrite Observations: Fe-sulphide altered to limonite at the rim (pyrite or chalkopyrite).

More Related