Other
Scientific paper
Jun 1961
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1961gecoa..24..106w&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 24, Issue 1-2, pp.106-154
Other
5
Scientific paper
Two methods for the determination of combined nitrogen in rocks and minerals are described: 1. (1) Determination of total combined nitrogen by decomposition of the rock by fusion with NaOH in a closed system, and solution of the melt in water. By this method of decomposition a part of the existing NH 3 is oxidized to NO 3 therefore it is impossible to determine NH 3 and NO 3 separately. The NO 3 is reduced by Devarda's alloy to NH 3 , which is distilled off with the primary NH 3 , adsorbed in a standard acid and determined colorimetrically by the Nessler method. 2. (2) Determination of NH 3 -N and NO 3 -N separately by decomposition of the sample with hydrofluoric acid at 90°C in a closed polyethylene-bottle, neutralization of the acid with NaOH and distillation and determination of the NH 3 as under (1). After that determination of NO 3 as NH 3 by reduction by Devarda's alloy. In both methods the NH 3 can be determined with an accuracy of 10%, for amounts less than 10 ± 1 g/ton. The error of the NO 3 determination is 25% and the sensitivity is 5 g/ton. In 400 rock and mineral samples NH 3 -N and NO 3 -N were determined mainly by the second method. Besides this the water-soluble nitrogen was determined in all magmatic rocks and minerals. The results show that nearly all magmatic rocks contain NH 3 -N, ranging between 5 and 50 g/ton, of which approximately one-half is water-soluble. There exists no characteristic difference between the different groups of rocks. Some rocks, which are not fully degassed, contain more NH 3 than the average, up to 150 g/ton. The average content of magmatic rocks is 20 g NH 3 -N/ton. NO 3 -N was not found. The distribution of the NH 3 -N between the different minerals of a rock was determined by separation of some granites, granodiorites and a basalt into their mineral constituents. Muscovite and biotite are richest in NH 3 -N (average of 60 and 33 g/ton), feldspars contain less (20 g/ton), and quartz least (13 g/ton). Late-magmatic minerals such as zeolites are higher in NH 3 -N than the rocks in which they occur, and the same is true for hydrothermally altered minerals (chloritization and sericitization). The distribution of the NH 3 -N between the different magmatic rocks and minerals and the presence of water-insoluble NH 3 -N in nearly all magmatic rocks leads to the conclusion that the NH 3 -N is of primary magmatic origin. The existence of nitrides in rocks is discussed and is considered to be improbable. The NH 3 -N content of sedimentary rocks is higher than in magmatic rocks. Clays and clayslates contain in the average 580 g NH 3 -N/ton, sandstones 135 g/ton and limestones 70 g/ton. Several series of sediments show that the NH 3 -content is dependent on the content of micas and clayminerals. NO 3 -N was found in minute amounts (5-20 g/ton) in surface sediments, some saline clays and in limestones. Average clays and sandstones contain no NO 3 -N. Metamorphic sediments contain much less NH 3 -N than the unaltered rocks. The NH 3 -N content of paragneisses and orthogneisses is variable, but in the average paragneisses contain more NH 3 -N than orthogneisses. Finally the average NH 3 -N content of the lithosphere is estimated.
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