| Reference Type | Journal (article/letter/editorial) |
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| Title | Iridescent anthophyllite-gedrite from Simiuttat, Nuuk district, southern West Greenland composition, exsolution, age |
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| Journal | Mineralogical Magazine | ISSN | 0026-461X |
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| Authors | Rodgers, K. A. | Author |
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| Kinny, P. D. | Author |
| McGregor, V. R. | Author |
| Clark, G. R. | Author |
| Henderson, G. S. | Author |
| Year | 1996 (December) | Volume | 60 |
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| Page(s) | 937-947 | Issue | 403 |
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| Publisher | Mineralogical Society |
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| Download URL | https://rruff.info/doclib/MinMag/Volume_60/60-403-937.pdf+ |
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| DOI | doi:10.1180/minmag.1996.060.403.08Search in ResearchGate |
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| Mindat Ref. ID | 122 | Long-form Identifier | mindat:1:5:122:5 |
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| GUID | 71978f66-1471-457b-b8c2-30c51f7485f9 |
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| Full Reference | Rodgers, K. A., Kinny, P. D., McGregor, V. R., Clark, G. R., Henderson, G. S. (1996) Iridescent anthophyllite-gedrite from Simiuttat, Nuuk district, southern West Greenland composition, exsolution, age. Mineralogical Magazine, 60 (403) 937-947 doi:10.1180/minmag.1996.060.403.08 |
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| Plain Text | Rodgers, K. A., Kinny, P. D., McGregor, V. R., Clark, G. R., Henderson, G. S. (1996) Iridescent anthophyllite-gedrite from Simiuttat, Nuuk district, southern West Greenland composition, exsolution, age. Mineralogical Magazine, 60 (403) 937-947 doi:10.1180/minmag.1996.060.403.08 |
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| In | (1996, December) Mineralogical Magazine Vol. 60 (403) Mineralogical Society |
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| Abstract/Notes | AbstractGolden iridescent, <1–100 mm crystals of alternating lamellae of anthophyllite and gedrite constitute the bulk of orthoamphibolite pods within quartz-cordierite gneisses of the Akulleq terrane at Simiuttat, SW Greenland. X-ray powder diffraction powder gave a = 18.526(7),b = 17.979(15), c = 5.285(23) Å; a single crystal has a = 18.546(7), b = 17.950(16), c = 5.280(1) Å, space group Pnma with some reflections being notably broader than others. Spot EMPA yielded composite analyses: AlIV = 0.89–1.3, Mg/(Mg+Fe2+) = 0.57–0.61, Na/AlIV = 0.22–0.26. AFM imaging of {210} cleavage surfaces, showed a uniform corrugated morphology parallel to [001]; wavelength was 190–350 nm, mean 250 nm, amplitude 3 nm. A plan view resembles TEM images of (010)-parallel exsolution textures of orthoamphiboles. A second set of corrugations may crosscut the [001]-parallel ridges at 20–25°, akin to reported lamellar intergrowths developed parallel to both (010) and (120). Unequivocal evidence linking topography with lamellae is absent. In contrast to the conventional multi-layer reflector model, the ridged surface provides an additional origin for iridescence, acting as a diffraction grating. Included zircons, 50–10 μm, have Hf/Zr = 0.008–0.012, Hf+FeIIc. 0.16. 207Pb/206Pb ages are from 2690 to 2770 Ma, averaging 2732±10 Ma. Coexisting, included Th-, La-, Ce-, Pr-, Nd-, Gd-, Y-monazites have 207Pb/206Pb ages from 2680 to 2720 Ma, averaging 2707±12 Ma. The included crystals grew during a late Archaean metamorphism that produced overgrowths on zircons within gneisses to the north, but with Simiuttat grains showing a more complex history. The lamellae may have developed at the same time, or during a reheating c. 2550 Ma, or in a subsequent Proterozoic metamorphism. |
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