1 / 16

Optical Mineralogy

Optical Mineralogy. WS 2012/2013. Exam week…. Final week of semester (4–8 February ) 3 hours at your normal Übung time 1 hour theory , 2 hours practical Simple pass or fail . Last week…. Length fast (Hauptzone -), length slow (Haup tzone +) Twinning Zoning Exsolution

rafiki
Télécharger la présentation

Optical Mineralogy

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. Optical Mineralogy WS 2012/2013

  2. Exam week…. • Final weekofsemester (4–8 February) • 3 hoursatyour normal Übung time • 1 hourtheory, 2 hourspractical • Simple pass orfail....

  3. Last week…. • Length fast (Hauptzone -), lengthslow (Hauptzone +) • Twinning • Zoning • Exsolution • Unduloseextinction • Howthediagrams in Tröger relatetotheopticalpropertiesofminerals

  4. Addition Example: Minerals with small birefringence (e.g. Quartz, Feldspar) Mineral = 100 nm (1o Grey) in diagonal position: GMineral = 100 nm (1o Grey) GGips = 550 nm (1oRed) Gobs = GMineral + GGyps  Gobs = 650 nm (2o Blue) ? Whentheinterferencecolouris 1ohigher (addition), thenthe NE-SW directionisthehighern - slowray (parallel tonofthegypsumplate). 1o Grey 2o Blue Withanalyseronly Withanalyserandcompensator

  5. Subtraction Turn the stage through 90°(Mineralstays at 100 nm) GMineral = 100 nm (1o Grey) GGips = 550 nm (1oRed) Gobs = |GMineral – GGips|  Gobs = 450 nm (1o Orange) ? Whentheinterferencecolouris 1olower (subtraction), thenthe NE-SW directionisthelowern - fast ray. 1o Grey 1o Orange Withanalyserandcompensator Withanalyseronly

  6. Hauptzone + or -?

  7. Optical character Long dimension of mineral is parallel to the slow ray(n , nZ) = LENGTH SLOW = HAUPTZONE + Long dimension is perpendicular to the slow ray (n , nZ) = LENGTH FAST = HAUPTZONE - sillimanite zoisite

  8. Optical character and Hauptzone Uniaxialminerals…. Prismatic crystal: If HZ + and Optically + If HZ - and Optically - Tabular crystal: If HZ + and Optically - If HZ - and Optically +

  9. Conoscopiclight – looking down an optic axis Divergent light throughthecondensor  Light cone (±30°) Objective lens What do wesee? N-S Analysator Mineral Condensor Variousslicesthroughtheindicatrix  INTERFERENCE FIGURE W Polariser E

  10. Conoscopic ray paths Retardation () is NOT constant! • n dependent on angle  Different interference colours

  11. Uniaxial interference figure O E Fig. 7-14 • Colour rings showing interference colours = ISOCHROMES • Crossing lines that remain in extinction = ISOGYRES • Intersection of isogyres = MELATOPE = the OPTIC AXIS (c) • Sectors between the isogyres = QUADRANTS • Interference colours increase with distance from the melatope (c-axis) • o-ray tangential, e-ray radial II I III IV

  12. Measuring the optical character (+) ng (+) Mineral withgypsumplate: • NE & SW: ne’ || ng Addition • NW & SE: no || ng Subtraction • Isochromes in I. and III. quadrantsarehigherbyoneorder • Isochromes in II. and IV. quadrantsarelowerbyoneorder • Isogyresred-violet (1º red) Close tothemelatope (G≈ 100 nm) • 2° blue (650 nm) in NE & SW (100+550) • 1° yellow (450 nm) in NW & SE (100-550) 2 1 no ne’ no ne’ Sub Add Add Sub ne’ ne’ no no 4 3 (+) Mineral: ne' > no neslowray

  13. Measuring the optical character (-) ng (-) Mineral withgypsumplate: • NE & SW: ne’ || ng Subtraction • NW & SE: no || ng Addition • Isochromes in I. and III. quadrantsarelowerbyoneorder • Isochromes in II. and IV. quadrantsarehigherbyoneorder • Isogyresred-violet (1º red) • Close totheisogyre (G≈ 100 nm) • 1° yellow (450 nm) in NE & SW (100-550) • 2° blue (650 nm) in NW & SE (100+550) 2 1 no ne’ no ne’ Add Sub Sub Add ne’ ne’ no no 4 3 (+) Mineral: ne' < no ne fast ray

  14. Uniaxial Optic Axial Figures (OAF) withoutgypsumplate: same for (+) and (-) (+) withgypsumplate blue in I. quadrant (-) withgypsumplate yellow in I. quadrant

  15. OAF with uncentredmelatope (Z) KonoskopischeBilderoptischeinachsigerKristallebeiunterschiedlicherSchnittlage; Isochromatensind in Grautönendargestellt. In der oberenReihesindSchnittlagen fast senkrechtzuroptischenAchseskizziert, in der unterenReihedeutlichschrägerzuroptischenAchse, so dass das Isogyrenkreuzaußerhalb des Gesichtsfeldesliegt.

  16. How do we get an OAF? • In XN, find a grain that remains in extinction through 360º - centre it • Change to high-powered objective and focus • Make sure grain stays in field of view • Maximise light (open diaphragm, insert sub-stage lens) • Remove left ocular • You should see an interference figure - draw it • Insert gypsum plate and note optic sign

More Related