Other
Scientific paper
Mar 1956
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1956gecoa...9..105w&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 9, Issue 3, pp.105-114
Other
5
Scientific paper
The influence of the salt content on the filling temperature of Sorby-inclusions (primary, unaltered inclusions filled with a homogeneous gas-free liquid) was experimentally determined-by the use of artificial inclusions. Capillary tubes made of soft soda glass (Jena No. 20), which after having been Filled with salt solutions of fixed concentrations were sealed under vacuum, served as artificial inclusions. The refractive indices of the inclusion-contents of eleven quartz, two beryl, and six topaz crystals of different origin were measured by a method which had been modified for this special purpose, and dates back to kohlrausch. It consisted in measuring the critical angle of reflection in reflected light. The crystal is embedded in an immersion liquid of equal refractive index. This offers the advantage that for the transition crystal surface/immersion liquid the light is not refracted, and therefore each inclusion plane (having any orientation to the outside crystal planes) can be used for the measurement, which was not possible with methods formerly employed. The refractive indices of the included liquids ranged from n = 1·33-1·34, in one case (quartz No. 14) n = 1·37. They correspond to a salt concentration of 0-5 per cent, respectively 25 per cent. The refractive index of the liquid CO 2 was determined to n = 1·15-1·18, and for gas bubbles or inclusions without liquid phases to N = 1·00. p]A critical discussion of former gas analyses shows that by far the largest part of the determined gases diffuse from outside through the heating vessel at high temperatures. These gases can possibly react with either adsorbed gases (adsorbed by the mostly powdered samples) or certain elements of the sample itself. Therefore, a description of an apparatus and an analytical method is given which exclude these sources of error. The crystals are heated under vacuum until they decrepitate. The escaping gases are determined qualitatively by fractional combustion and/or by condensation, by spectrographic photographs, and quantitatively by measurement of pressure differences (manometric micro-gas-analysis). The results of the gas analyses of quartz, beryl, and topaz crystals by. this method show agreement with the results of the microscopical investigation of the inclusion contents: H 2 O predominates in all of the examined samples (also in those that contain liquid CO 2 ), and amounts to 73 vol per cent and more. In cases where a microscopical examination revealed that several inclusions of a crystal contained liquid CO 2 , about 25 per cent CO 2 were found by gas analyses. The amount of CO 2 is always of the magnitude of per cent, also in cases where no liquid CO 2 is visible. The whole quantity of gases (including water in the gaseous state--contrary to most of the former analyses) amounts to 0·05-0.77 cm 3 /g mineral. The proportion Permanent gas/Condensable gas (CO 2 ) equalled, with the exception of one sample (topaz 21), 1 : 10 or less. Free O 2 was not discovered. The C-bands of spectral photographs of permanent gases obtained from two of the examined samples (beryl 16, topaz 21) indicate the presence of CH 4 . Other C-containing gases (C 2 H 4 , C 2 H 6 ), which because of their similar vapour pressure might come into consideration, are (1) burned more easily than CH 4 , and would consequently have been burned at the preceding CO and H 2 combustion, and are (2) certainly much less abundant than CH 4 in natural crystals. In one of the analyses (quartz No. 1) the presence of He and Ar could spectrographically be proved. An historical review is given on available analyses of substances soluted in inclusion liquids. The results are listed in a table. The statements concerning the concentration range from almost pure H 2 O to saturated solutions. Analyses carried out by the author (of the same crystals that had previously served for the gas analyses) furnished concentration values of usually 0-5 per cent, in one case (beryl No. 18) concentrated solution. Semi-quantitative spectrographic determinations of the cations indicated the presence of Na, Ca, K, in order of abundance. K was found only in a third of the examined samples. Michrochemical SO 4 '' and titrimetrical Cl' determinations revealed in all samples a strong prevalence of Cl' over SO 4 ''. These determinations of the cations and anions confirm the results obtained by measurements of refractive indices. The concentrations derived by these two different methods are of the same order of magnitude.
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