A Summary of Progress in Petrography. in 1887-1896 |
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Page 12
... angles a , ẞ and y are all nearly 90 ° , so that the combination is somewhat similar to the combination of orthorhombic aragonites to produce an apparently hexagonal form . The axial ratio on the assumption of triclinic symmetry becomes ...
... angles a , ẞ and y are all nearly 90 ° , so that the combination is somewhat similar to the combination of orthorhombic aragonites to produce an apparently hexagonal form . The axial ratio on the assumption of triclinic symmetry becomes ...
Page 14
... angles at different temperatures . The second is confined to refractive phenomena , such as the refractive index for different wave lengths . The third and fourth contain calculations of the values of the optical constants , and the ...
... angles at different temperatures . The second is confined to refractive phenomena , such as the refractive index for different wave lengths . The third and fourth contain calculations of the values of the optical constants , and the ...
Page 15
... angle 2 En2 = 63 ° 3 ′ , and the extinction in the macropinacoid is 16o - 17 ° , in acute B. Fibres of sideronatrite show a slight pleochroism , with a pale straw - yellow color parallel to the longer axis , and no color at right angles ...
... angle 2 En2 = 63 ° 3 ′ , and the extinction in the macropinacoid is 16o - 17 ° , in acute B. Fibres of sideronatrite show a slight pleochroism , with a pale straw - yellow color parallel to the longer axis , and no color at right angles ...
Page 17
... angles . Twinned crystals are quite common , the combination possessing an hexagonal habit.- -The rare zeolite mordenite has been discovered by Pirsson 19 in the cavity of an amygdaloidal basalt , forming fragments in a breccia near ...
... angles . Twinned crystals are quite common , the combination possessing an hexagonal habit.- -The rare zeolite mordenite has been discovered by Pirsson 19 in the cavity of an amygdaloidal basalt , forming fragments in a breccia near ...
Page 18
... angles , etc. The angle between the cleavage lines is 89 ° 30 ' , and the refractive indices for sodium light , a = 1.5224 , 91.5264 , 7 = 1.5295 . The optical angle is 2V 83 ° 41 ' .- A pure white zine sulphide is mentioned by Mr ...
... angles , etc. The angle between the cleavage lines is 89 ° 30 ' , and the refractive indices for sodium light , a = 1.5224 , 91.5264 , 7 = 1.5295 . The optical angle is 2V 83 ° 41 ' .- A pure white zine sulphide is mentioned by Mr ...
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acid Al,O alteration Amer AMERICAN NATURALIST analysis andalusite angle aragonite augite axial ratio basalts beryl biotite brucite Bull calcite calcium chlorite cleavage Colby University color colorless composition constituents containing cordierite corresponding crystalline crystals density described diabase double refraction dyke eruptive rocks Fe,O Fe₂O feldspar FeO MgO CaO FeO MnO forms formula Franc gabbro-diorites gabbros garnet Genth gneisses granite granulites ground-mass H₂O habit hexagonal hornblende humite hypersthene imbedded inclusions Jour Kryst leucite masses melanophlogite metacinnabarite mica mineral MINERALOGY AND PETROGRAPHY.¹ Mitth molecules muscovite Neues Jahrb nosean occur olivine optical original orthoclase ottrelite parallel Penfield Petrog PETROGRAPHY.¹ Petrographical phenacite plagioclase plane plates polymorphism prismatic produced pseudomorphs pyroxene quartz regarded rock individual Rosenbusch schistose schists serpentine silica sodium soluble specific gravity specimens spinel structure substance sulphur symmetry tabular temperature tonalite tourmaline twinned varieties W. S. Bayley Waterville yielded Zeits zircon zone
Popular passages
Page 19 - The plane of the optical axes is perpendicular to the plane of symmetry, and makes with c an angle of °7 in acute /9. A = b. 2H na = 104° 27'.
Page 14 - The larger part of the dust is thought to be a sediment from the air, and to have been obtained by it from a region of crystalline schists. The chondri, on the other hand, are thought to be of cosmic origin, since they are similar to the chondri obtained in deep-sea soundings. If the amount of the dust collected from the snow in Greenland represents the fall of one year, the total amount falling upon the entire surface of the earth in this time is 125 million kilograms, equivalent to a cube of thirty-one...
Page 14 - Wiilfing 21 for investigation, by whom it has been found to consist in greater part of feldspar, quartz, mica, and hornblende. There are present in it also garnet, zircon, magnetite, augite, and sillimanite, and with them is mixed a nitrogenous organic substance. The most interesting constituents of the dust...