Although only part of the information from the x-ray fluorescence geochemical experiment has been analyzed, it is clear that the experiment was highly successful. Significant compositional differences among and possibly within the maria and highlands have been detected. When viewed in the light of analyzed lunar rocks and soil samples, and the data from other lunar orbital experiments (in particular, the Apollo 15 gamma-ray spectroscopy experiment), the results indicate the existence of a differential lunar highland crust, probably feldspathic. This crust appears to be related to the plagioclase-rich materials previously found in the samples from Apollo 11, Apollo 12, Apollo 14, Apollo 15, and Luna 16.

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Recent advances in the x-ray fluorescence analysis of the light elements offer the advantage of speed and an accuracy approaching that of wet chemical procedures In addition to Fe, Mn, Ti, Ca, and K, the elements P, Si, Al, and Mg, previously considered too light to be determined quantitatively, can now be included in the scheme of analysis X-ray fluorescence analysis of these light elements is primarily confined to layers close to the surface, with the attendant problems of particle size, mineralogic history, and absorption differences owing to compositional variation among samples Fusion of the sample with a suitable flux eliminates problems of particle size and mineralogic differences Simple fusion, however, does not eliminate absorption differences due to variation in matrix By introducing into the fusion melt a strong absorber (La2O3) for the light elements, the variation in concentration of absorbing elements in the unknown sample will not materially affect the overall absorption of the fused mass for the elements being determined This permits the use of a single set of standards regardless of the rock type to be analyzed The x-ray fluorescence method has been applied to the analysis of a wide variety of rock types such as granite, diabase, dunite, limestone, dolomite, and phosphate rock, with results that compare favorably with chemical values

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