Dept., Univ. of ela as are, 'i?ewark, DE Approximately 130 low specific gravity ((2.601, high silica

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HIGH (760%) SiO LUNAR GLASS%. ir.f. Glass, Geoloey Dept., Univ. of ela as are, 'i?ewark, DE. 1971 1 Approximately 130 low specific gravity ((2.

1 HIGH (760%) SiO LUNAR GLASS%. ir.f. Glass, Geoloey Dept., Univ. of ela as are, 'i?ewark, DE Approximately 130 low specific gravity ((2.601, high silica p602) glass particles recovered from a 4.88 gm sample of lunar fines (14259,20) using heavy liquids.?he major element compositions of-90 of the high silica glass particles were determined by electron microprobe analyses. Silica contents range from-60% to nearly 100%. Approximately 70 of the particles were homogeneous. Histograms and oxide variation diagrams were used to divide the homogeneous glasses into several groups (Table 1). Pifty-seven (-81%) of the homogeneous glasses fall into a group with SiO content ranging between 72 and 78%. The rest have somewhat gigher or lower silica ccntents (groups A, B and Y,?able I), and generally do not contain vesicles or crystalline inclusions. The glasses with silica contents between 72 and 78% fall into three well-defined groups based on their FeO contents. The glasses in the largest group (group E) have FeO contents clustering around 2.65%. The glasses in this group do not contain vesicles or crystalline inclusions. The glasses in the second largest group (group C) have FeO contents clustering around 0.5%. The third group (group D) contains glasses with intermediate Fee contents (1 to %). The group C and D glasses, in contrast to the group E glasses, contain abundant crystalline inclusions. The crystalline phases identified are, in order of their abundance t pyroxene, Si02, Ili-F e, apatite, ilmenite, K- feldspar, plagioclase, metallic iron and troilite. The range and modal composition of the glasses reported here are similar to those previously reported for high silica glasses from lunar fines. Two possible origins of the high silica glasses seem most reasonable8 1) they are fragments of interstitial or residual glass from mare basalts; or 2) they are impact-produced glasses from a "graniticw source rock. liumerous authors have reported the presence of high silica interstitial or residual glass up to 150 across in the mare basalts, The size, shape, abundance, mineralogy and major element composition of the glasses (except those of group E) reported here are consistent with their being fragments of interstitial glass from mare basalts. The fact that high silica glass fragments have not been reported in Apollo 16 (highland) soils also supports their being fragments of interstitial glass from mare basalts.?he group E glasses also have major element compositions similar to the high silica interstitial glasses found in mare basalts. However, they seem to have slightly higher Na20 ( %) and slightly lower Cab ( %) contents than interstitial glasses with the same Si02 and FeO contents, which generally have less than 1% Na20and often have more than 1.5% CaO.

2 High Si02 Lunar Glasses B.P. Glass '?he lack of crystalline inclusions in the group E glasses also suggests that they are not fragments oe interstitial glass. It 1s tempting, therefore, to suggest that these glass particles were derived by shock melting from a "graniticv source rock. However, there are two problems with such an origin. First of all, the group E glasses do not contain any shocked crystalline inclusions or Ni-f e spherules of meteoritic composition that would support such an origin. Secondly, all of the group E glasses are fragments; none are splash forms (spheres, teardrops, dumbbells, etc.). An alternative origin is that these glasses are the products of lunar acidic volcanism. This hypothesis is supported by their homogeneity not only within a single particle, but from particle to particle. I Table 1. Average Composition of High Silica Glass Groups S i02 T i0 A1 a, F e8 MgO C a0 Na2C K2 R.I. Analysis #72 f Range Ave. Group A Group B Group C (3) (2) (18) Group D Group E Group F Analys is (10) (30) (2) #80 * S i G 'l ic z ~l , F e big 0 0, CaO PJa K R.I (4) (15) (2) Ave e ( ) = number of analyses f Homogeneous glass particle with lowest Si02 content. - + = one stand.ard deviation * The only high silica spherule found.

3 ELECTRICAL PROPERTIES OF APOLLO 17 ROCK AND SOIL SAMPLES AND A SUMMARY OF THE ELECTRICAL PROPERTIES OF LUNAR MATERIAL AT 450 MHz FREQUENCY. T. Gold, E. Bilson and R. L. Baron, Center for Radiophysics and Space Res., Cornell University, Ithaca, N.Y., Figure 1 shows the average dielectric constant vs. density Rayleigh curve for Apollo 17 soil samples-4 samples from different locations, including the orange soil, and data points for two Apollo 17 rock samples. This curve lies very close to the Apollo 11 and 12 curve, see Figure 2, which is included for comparison. The data points for the solid samples seem to be approximately on the extension to higher density of the powder Rayleigh curve. This is interesting because the Apollo 17 dust and rock samples display a great variety of chemical composition but for each rock type there is a corresponding dust type. This was not the case for example with the Apollo 11 and 12 samples and data points for the solid rocks did not fit the Rayleigh curve for dust. Figure 3 shows the voltage absorption vs. density Rayleigh curves for Apollo 17 soil samples and data points for the rock samples. Again the solid data points lie close to the extension of Rayleigh curves representing dust of similar chemical composition as the rock. (Actually soil sample and rock sample are not as close mineralogically as indicated by the absorption curve ) Rock is an example of a very lossy solid material whereas the absorption in is less than in any terrestrial rock examined (1). Figure 4 shows, for comparison, voltage absorption vs. density Rayleigh curves for Apollo 11, 12, 14, 15 and 16 samples. The Apollo 17 samples display a greater range of absorbency than samples from any other Apollo missions. In Figure 5 absorption lengths, measured in rock samples from all the Apollo missions, are shown as a function of the iron + titanium concentration in these samples. The density of each rock sample is - 3 indicated in parenthesis, the density range being g cm. At these densities the absorption length vs. density curve is rather flat, so that a small change in density does not effect the absorption significantly. The absorption length in rocks seems to be clearly related to the iron+titanium content. A similar finding was reported by Olhoeft and Strangway (2). Figure 6 relates the albedo (which in turn was also related to the Fe + Ti content (3)) and the absorption length in soil samples. Again a clear correlation seems to exist. Samples and are somewhat outstanding. It is very interesting that in the albedo vs. surface (Fe + Ti) concentration curve and are also outstanding(3). These samples have probablyahigh albedo because they contain a few percent of very

4 ELECTRICAL PROPERTIES... T. Gold et al. light, iron poor material. Olhoeft et a1 (4) demonstrated the effects of short- and long- period exposure of lunar dust samples to moisture, particularly significant was the short-term exposure effect on the absorption properties. Our samples were baked at 150 C in high vacuum for two days prior to the measurement (made in air). It is possible though that short-term exposure effects altered our results, the magnitude of these effects at high frequencies has not been determined yet. However our results show no clustering of data obtained with samples from the early missions (Apollo 11, 12, 14) vs. data representing samples from later missions, thus we see no obvious long-term exposure effects due to sample handling. The high absorption in Apollo 11 and 12 samples seem to be related to the low albedo (high Fe + Ti content) in these samples and similarly high absorption is found in a low albedo Apollo 17 dust sample. In summary: absorption lengths of wavelengths at 1.6 gati3 density are not unusual on the Moon for compacted powders and the absorption range in lunar rocks is wavelengths at 450 MHz frequency. In terrestrial samples the absorption length range at 450 MHz is wavelengths (1). The existence of these great absorption lengths on the Moon is very important for the interpretation of radar results. In the future perhaps depths of several kilometers in the lunar surface could be investigated by suitable radar systems. References: (1) Campbell, M.J., and Ulrichs, J., 1969, Journal of Geophys. Res., 74, p (2) Olhoeft, G.R., and Strangway, D.W., 1975, Earth and Planetary Science Letters, 24, p (3) Gold, T., Bilson, E., And Baron, R.L., 1976, The Correlation Between the Albedo and the Surface Chemical Composition in Lunar Soil Samples in "Lunar Science VII", The Lunar Science Institute, Houston. (4) Olhoeft, G.R., Strangway, D.W., and Pearce, G.W., 1975, Proc. Lunar. Sci. Conf. 6th, p Figure 1. Figure 2.

5 ELECTRICAL PROPERTIES... T. Gold et al. Figure 3. Figure ,7w1 1207c The A~SD~P~IM Length is the Colculoled Volue far 12 g ~ r n Densty - ~ Figure 5. Figure 6.

6 THE CORRELATION BETWEEN THE ALBEDO AND THE SURFACE CHEMICAL COMPOSITION IN LUNAR SOIL SAMPLES. T. Gold, E. Bilson, and R. L. Baron, Center for Radiophysics and Space Res., Cornell University, Ithaca, N.Y., The correlation of the albedo and the iron + titanium concentration in numerous ground-up lunar rock and soil samples from all the Apollo landing sites has been investigated in detail. In Figure 1 the data points (with the exception of that of the iron poor, very high albedo soil samples 73241, 67601,.63501) are fitted to the exponential law: A=A e -na where A is the observed albedo, A. is the hypothetical aybedo at n=o (the law does not seem to be valid for soil samples at very low n values), n is the iron + titanium concentration (surface or bulk) observed and o is the absorption coefficient. The concentration error bars indicate the Auger concentration.extremes obtained with taking spectra on various spots of the same sample, the albedo error Qars refer to the lowest and highest albedo mea- sured at 5500A wavelength at 8' illumination angle and was normalized at MgO. There seems to be three distinct curves. 1. Albedo of soil samples vs. bulk iron + titanium concentration (the latter obtained from the literature). 2. Albedo of soil samples vs. surface iron + titanium concentration (determined by Auger electron spectroscopy) (1, 3). 3. Albedo of ground-up rock samples vs. surface (approximately same as the bulk) iron + titanium concentration. In our first publication on this subject (1) we includ-ed similar curves but the albedo was plotted as a function of iron concentration alone. Recently we have analyzed titanium rich rock and soil samples from the Apollo 11 and 17 missions and discovered that the data fits the exponential law best when n includes both the iron and titanium concentrations. This is to be expected on the basis that both iron and titanium provide absorption centers. From these curves the following deductions can be made: a. The albedo of the soil samples is approximately three times lower than that of ground-up rock samples having the same bulk iron + titanium concentration, see curves 1 and 3. At the same time the soil samples have higher (2-3times) iron + titanium concentration on their surface than bulk concentration in these elements, see curves 1 and 2. The soil therefore must have suffered a treatment that affected both the albedo and the surface iron and titanium. b. The fact that curves 2 and 3 are clearly separate suggests that a different mechanism must be responsible for light absorption on the surface of soil samples and on the surface of freshly ground-up rock samples. Our Auger results and recent ESCA information (2) suggest

7 ALBEDO AND SURFACE CHEMISTRY CORRELATION. T. Gold et al. that at least some of the iron and titanium is reduced on the surface of soil grains to a lower oxidation state than their state in the bulk. In the case of iron this is the metallic state. Research is under progress for the determination of the thickness of the chemically altered skin on soil grains and its optical significance. The possibility exists that the above skin proves to be too thin to be optically significant and the increased light absorption in soil samples is due to a crystallographic change in the lattice. This change then seemingly goes in step with a chemical change on the outer surface and is very probably due to the same weathering agent. We reported recently (3) on solar wind simulation experiments with 2 kev protons. A dose of protons, equivalent to a few thousand years of solar wind rendered the Auger spectrum of an Apollo 14 ground-up rock sample identical (within experimental uncertainty) to that of the Apollo 14 soil of the same bulk composition. The principal change induced by the ion bombardment was the increased iron concentration on the surface of the rock powder. The albedo of the powder decreased however only slightly by the above dose. Since then we repeated the above experiment with 2 kev a-particles using much higher irradiation doses. We found that an approximate equivalent of 25,000 years of solar wind was needed to darken the ground-up rock to the albedo of the soil. At this stage we suppose that this much higher dose, necessary to darken the rock to lunar soil albedo, corresponds to the dose needed to alter the chemistry down to a thick enough layer on the grains to cause the required optical effect. Comparison and correlation of the surface and bulk concentrations of different elements is important for the understanding of the origin and the formation mechanism of the chemically altered skin on soil grains (3). Previously we reported data on the Fe, Ti and Ca concentrations calculated from Auger Fe/O, Ti/O and Ca/O data (3). With the help of recent improvements on our Auger system we have preliminary results on Si concentrations. Sample \- 1 rock zoil Si (surface) in atomic percent Si (bulk) in atomic percent The above data indicate no systematic change of the surface Si concentration from the bulk Si concentration in soil samples. Housley and Grant (2) reported somewhat different findings concerning Si on one sample using ESCA. Clearly more data is needed for good statistical significance. It is very likely however

8 ALBEDO AND SURFACE CHEMISTRY CORRELATION. T. Gold et al. that the concentration of Ca and that of all the other elements lighter than Ca is decreased on the surface whereas the concentration of Fe and Ti is increased. The mass dependence of the chemical change on the surface can be most readily explained by a sputtering process by solar wind ions. References: (1) Gold, T., Bilson, E., and Baron, R.L., 1974, Proc. Lunar Sci. Conf. 5th, p (2) Housley, R.M., and Grant, R.W., 1975, Proc. Lunar Sci. Conf. 6th, p (3) Gold, T., Bilson, E., and Baron, R.L., Sci. Conf. 6th, p , Proc. Lunar L l l i i l l l,, l l ( 1, 1 1, 1, IS 19 Alomfc Percent (Fe+ TI ) Figure 1

The Surprising Lunar Maria

1 of 5 posted June 23, 2000 The Surprising Lunar Maria Written by G. Jeffrey Taylor Hawai'i Institute of Geophysics and Planetology The lunar maria, the dark, smooth areas on the Moon, formed when lava