guide to thin section microscopy - Mineralogical Society of America

More documents

Recommendations

Info

Guide to Thin Section Microscopy Double refraction Raith, Raase & Reinhardt – February 2012 Figure 4-30. ∆n-d Interference colour chart after Raith-Sørensen. The birefringence values of the colour chart are correlated with common rock-forming minerals. The use of the colour chart for mineral identification and determination of crystal thickness is explained in the text and is further demonstrated in Fig. 4-32. 93
Guide to Thin Section Microscopy Double refraction arranged as a function of birefringence and crystal (or thin section) thickness (Fig. 4-30). The resulting, more complex hyperbolic colour arrangement has been calculated by Bjørn Eske Sørensen using MATLAB. The correlation between the birefringence value of an unknown mineral in a section of known thickness and the mineral's interference colour can be conceived intuitively (Fig. 4-32, right-hand side). Similarly, reading the thin section thickness from the reconfigured colour chart using the maximum interference colour of a known mineral is straightforward. The dependence of interference colour on thin section thickness is immediately evident. However, for getting the numerical correlation between retardation and ∆n, or between retardation and d, the Michel-Lévy chart is the better choice. When using interference colours for the determination of minerals it has to be kept in mind that the retardation which accumulates as the waves pass through the crystal is not only dependent on ∆n of that particular crystal section, but also on the thickness of the sample. In order to correlate interference colours and birefringence values directly, the thin section thickness has to be known. Therefore, thin sections are prepared with a defined standard thickness (commonly 25 or 30 μm). However, there may be reasons to deviate from these standard values, for example, if the contrast of interference colours between low-birefringent phases is to be increased; or, to improve the contrast between differently oriented grains of extremely high-birefringent minerals, the interference colours can be reduced to a lower order (as in ultra-thin sections of carbonates). Raith, Raase & Reinhardt – February 2012 Figure 4-31. Relation between interference colour and grain (crystal) orientation of anisotropic minerals, using quartz, diopside and anhydrite as examples. A: The euhedral quartz crystals from a vein show creamy-white to dark grey first-order interference colours. Creamy-white crystals: sections parallel to the c-axis [max. birefringence (n e – n o ) = 0.009]; dark grey crystal: section nearly orthogonal to c [circular indicatrix section showing n o ; birefringence = 0]. B: The diopside grains in a calcsilicate rock show different interference colours, dependent on crystal orientation, ranging from second-order blue-green to first-order dark grey. Blue-green grain: section parallel to (010) resp. optic axial plane [max. birefringence (n z – n x ) = 0.031]; dark grey grain: section nearly orthogonal to one of the two optic axes [circular indicatrix section showing n y ; birefringence = 0]. C: The anhydrite grains show different interference colours, dependent on crystal orientation, ranging from third-order red to first-order (near-)black. Pale red grains: section parallel to (010) resp. optic axial plane [max. birefringence (n z – n x ) = 0.044]; black grain: section orthogonal to one of the two optic axes [circular indicatrix section showing n y ; birefringence = 0]. 94
Page 1 and 2:
GUIDE TO THIN SECTION MICROSCOPY Se
Page 3 and 4:
Guide to Thin Section Microscopy Co
Page 5 and 6:
Guide to Thin Section Microscopy Pr
Page 7 and 8:
Guide to Thin Section Microscopy Te
Page 9 and 10:
Guide to Thin Section Microscopy Mi
Page 11 and 12:
Page 13 and 14:
Page 15 and 16:
Page 17 and 18:
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
Page 25 and 26:
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Guide to Thin Section Microscopy Me
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Guide to Thin Section Microscopy Cr
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
Guide to Thin Section Microscopy Cl
Page 49 and 50: Guide to Thin Section Microscopy Cl
Page 55 and 56: Guide to Thin Section Microscopy Tw
Page 57 and 58: Guide to Thin Section Microscopy Tw
Page 59 and 60: Guide to Thin Section Microscopy In
Page 61 and 62: Guide to Thin Section Microscopy Ex
Page 63 and 64: Guide to Thin Section Microscopy Re
Page 65 and 66: Guide to Thin Section Microscopy Al
Page 67 and 68: Guide to Thin Section Microscopy Op
Page 75 and 76: Guide to Thin Section Microscopy Co
Page 85 and 86: Guide to Thin Section Microscopy Li
Page 87 and 88: Guide to Thin Section Microscopy Do
Page 99: Guide to Thin Section Microscopy Do
show all

guide to thin section microscopy - Mineralogical Society of America

Create successful ePaper yourself

Delete template?

Save as template?