Diffraction and mossbauer studies of minerals from lunar soils and rocks

Constituents of lunar soils and rocks were studied by powder and singlecrystal x-ray diffraction. In addition to identification of minerals, including rare amphibole, mica, and aragonite, a detailed study of the important rock-forming minerals of the plagioclase, pyroxene, and olivine groups has begun. M?ssbauer spectra were recorded from lunar soils, ground rock samples, and separates of iron-bearing minerals. The proportions of iron-bearing minerals were estimated from computer-fitted areas for the bulk samples. The Fe(2+) in the lower-density fraction of pyroxene was ordered, whereas that of the higher-density fraction was disordered.     

Multielement analysis of lunar soil and rocks

Results for multielement analysis of lunar soil and of seven rocks returned by Apollo 11 are presented. Sixty-six elements were determined with spark source mass spectrography and neutron activation. U. S. Geological Survey standard W-1 was used as a comparative stanadard. Results indicate an apparent uniformity of composition among the samples. Comparison with solar, meteoritic, and terrestrial abundances reveals depletiozt of volatile elements and enrichment of the rare earths titaniunm, zirconium, yttriuntm, and hafnium. Althouglh there is an overall similarity of the lunar material to basaltic achondrites amid basalts, the differences suggest detailed geochemical processes to the history of this material.     

Cathodoluminescence properties of lunar rocks

Calcic plagioclase is the dominant luminescent mineral in crystalline rocks and breccias. Minor amounts of cristobalite and tridymite are also luminescent, as are trace grains of potassium feldspar. Two types of intergrowths of potassium feldspar with a silica phase, possibly quartz, were found in the breccias. Luminescence spectra of plagioclase show significant similarities to, and differences from, spectra of terrestrial plagioclase. Shock damage in the breccias is reflected in systematic changes in the plagioclase spectra, thus giving evidence of disordering on the angstrom scale. Associated extinction patterns seen between crossed Nicol prisms give evidence of disordering on the micrometer scale.     

Isotopic analysis of rare gases from stepwise heating of lunar fines and rocks

Highlights of a first effort in sorting out rare gases in lunar material are solar wind rare gases in abundance; variable (20)Ne/(22)Ne but constant (21)Ne/ (22)Ne ratios in fractions of the trapped neon; cosmogenic rare gases similar to those found in meteorites, except for copious (131)Xe in one rock but not in another; at Tranquillity Base a rock 4.1 x 10(9) years old which reached the surface 35 to 65 million years ago, amid soil whose particles have typically been within a meter of the surface for 10(9) years or more.     

Petrographic, mineralogic, and x-ray fluorescence analysis of lunar igneous-type rocks and spherules

Three lunar rocks show almost identical mineralogy but grain sizes that vary from basaltic to gabbroic. Clinopyroxene is zoned from augite to subcalcic ferroaugite compositions and is accompanied by decrease in Cr, Al, and Ti. Plagioclase is zoned from 93 to 78 percent anorthite. Olivine (68 percent forsterite) is present in one rock and apatite is rare. Cristobalite, ilmenite with Ti-rich lamellae, ulv?spinel (often Cr-rich), troilite, and kamacite are low in trace elements. Glassy spherules are of basaltic or feldspathic (92 percent anorthite) composition but contain abundant iron spheres of taenite composition (13 percent Ni). Four rock analyses by x-ray fluorescence show affinity with terrestrial basalts but with anomalous amounts of Ti, Na, Cr, Zr, Y, Rb, Nb, Ni, Cu, and Zn.     

Petrology of unshocked crystalline rocks and shock effects in lunar rocks and minerals

On the basis of rock modes, textures, and mineralogy, unshocked crystalline rocks are classified into a dominant ilmenite-rich suite (subdivided into intersertal, ophitic, and hornfels types) and a subordinate feldspar-rich suite (subdivided into poikilitic and granular types). Weakly to moderately shocked rocks show high strain-rate deformation and solid-state transformation of minerals to glasses; intensely shocked rocks are converted to rock glasses. Data on an unknown calcium-bearing iron metasilicate are presented.     

The remanent magnetization of lunar soils

The magnetic material in the lunar soils makes them potentially strong carriers of remanence and magnetically viscous. The soils therefore block remanence in the temperature range of the lunar diurnal cycle. This remanence is stable against alternating-field demagnetization. A mechanism whereby such hard natural remanent magnetization may be acquired by material buried in the regolith is proposed.     

Shock-wave damage in minerals of lunar rocks

The mineral fragments that constitute the Apollo 11 microbreccia and fines show a number of shock-induced microstructural effects including multiple twinning on (001) in clinopyroxene and incipient development of lattice-controlled discontinuities in olivine. These structures coupled with the effects of shock-induced melting as manifested by spherules and angular fragments of glass and their partly to completely crystallized equivalents indicate that Apollo 11 materials were subjected to weak to moderate shocks with associated peak pressures of the order of 100 to 200 kilobars.     

Search for magnetite in lunar rocks and fines

Magnetite crystals larger than 2 micrometers are absent from rocks and fines. Smaller opaque spheres in the fines can tentatively be identified as magnetite. Their concentration is not higher than 1 x 10(-6) particle per particle smaller than 1 millimeter. In the fines from the sampling site, the contribution of material similar to type 1 carbonaceous meteorites is insignificant, either because it never existed, or because it was evaporated or comminuted by impact or was diluted by indigenous material. Other magnetite habits typical of carbonaceous meteorites or possibly of cosmic dust or comets were also sought without success-such as rods, platelets, framboids, spherulites, and idiomorphic crystals.     

Neutron activation analysis of a particle returned from asteroid Itokawa

A single grain (~3 micrograms) returned by the Hayabusa spacecraft was analyzed by neutron activation analysis. This grain is mainly composed of olivine with minor amounts of plagioclase, troilite, and metal. Our results establish that the Itokawa sample has similar chemical characteristics (iron/scandium and nickel/cobalt ratios) to chondrites, confirming that this grain is extraterrestrial in origin and has primitive chemical compositions. Estimated iridium/nickel and iridium/cobalt ratios for metal in the Itokawa samples are about five times lower than CI carbonaceous chondrite values. A similar depletion of iridium was observed in chondrule metals of ordinary chondrites. These metals must have condensed from the nebular where refractory siderophile elements already condensed and were segregated.     

Potassium-argon ages of lunar rocks from mare tranquillitatis and oceanus procellarum

Crystalline rocks from Mare Tranquillitatis have yielded potassium-argon dates as old as 3.8 x 10(9) years. Crystalline rocks from Oceanus Procellarum give potassium-argon ages as old as 2.8 x 10(9) years. Evidently the maria are ancient features of the moon and were not formed contemporaneously, a conclusion that also has been verified by other methods. The potassium-argon ages of rocks from Oceanus Procellarum show much more loss of argon than the rocks from Mare Tranquillitatis, an indication that the rocks at Oceanus Procellarum have experienced more severe shock effects or longer cooling rates.     

Opaque minerals of the lunar rocks and dust from mare tranquillitatis

The opaque minerals in the lunar rocks 10047, 10050, 10057, 10059, 10068 and in the dust were studied. Rock 10047 contains ilmenite as a main component besides Al-bearing chromian ulv?spinel, a new Ti, Fe, Zr, Y, Ca silicate, troilite, cobaltian alpha Fe, minor hafnian baddeleyite and dysanalyte. Dysanalyte contains Ca, Ti, and Fe as major elements and shows concentrations (rare earth elements together approximately 10 percent) of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Hf, Y, and Zr plus traces of Nb, Ba, and Na. The chemistry of ilmenite in the igneous rocks shows no appreciable variations. A new mineral of the solid solution series MgTi(2)O(5)-FeTi(2)O(5) has also been encountered in the polymict breccias. The microbreccias and the fines contain meteorite debris indicating an impact origin.     

Sound velocity and compressibility for lunar rocks 17 and 46 and for glass spheres from the lunar soil

Four experiments on lunar materials are reported: (i) resonance on glass spheres from the soil; (ii) compressibility of rock 10017; (iii) sound velocities of rocks 10046 and 10017; (iv) sound velocity of the lunar fines. The data overlap and are mutually consistent. The glass beads and rock 10017 have mechanical properties which correspond to terrestrial materials. Results of (iv) are consistent with low seismic travel times in the lunar maria. Results of analysis of the microbreccia (10046) agreed with the soil during the first pressure cycle, but after overpressure the rock changed, and it then resembled rock 10017. Three models of the lunar surface were constructed giving density and velocity profiles.     

Instrumental neutron activation analyses of lunar specimens

Ten Apollo 11 specimnens were divided into 24 samtples. Sodillim contents of 8 diverse specimens clluster tightly abolit 0.3 percent. Plagioclase separated from sample 10044 contains aboltt 1.09 percent Na; barium is not enriched in the plagioclase separate. Contents of the rare earths are strikingly high, and relative abtmndances resemble those of calcium-rich achondrites or abyssal basalts but are depleted in Eu by factors of 2 to 3 and in La by about 20 percent. The plagioclase separate is enriched in Eu and pyroxenes (and opaqtte minerals are Eu-depleted. Fine fractions of 10044 are abotit 20 to 40 percent richer in most rare earths (50 percent for Eu) than coarse fractions, probably becaitse of the presence of small grains in which rare earths are mnarkedly concentrated. "Microgabbro" 10045 is imnpoverished, relative to the soil, in rare eartlhs and Hf. Ratios by mass of Zr to Hf are comlparatively low. Abttndances of Mn, Co, Fe, Sc and Cr stiggest systematic differences between igneous rocks on one hanid and breccias and "soil" on the other. Fromn the Co abuindances, no more than about 3 percent of the present "soil" can consist of chondritic mleteorite conitamination.     

Thermal conductivity of lunar and terrestrial igneous rocks in their melting range

The thermal conductivity of a synthetic lunar rock in its melting range is about half that of a terrestrial basalt. The low conductivity and increased efficiency of insulating crusts on lunar lavas will enable flows to cover great distances without being quenched by high radiant heat losses from the surface. For a given rate of heat production, the thermal gradient of the moon would be significantly steeper than that of the earth.     

Abundances of 30 elements in lunar rocks, soil, and core samples

Abundances of 30 elements in seven lunar rocks and soil were determined by instrumental and radiochemical activation analysis. Seven major and minor elements in chips from 27 rocks were determined by instrumental activation analysis. Abundances of ten bulk elements overlap for the breccia rocks and soil samples. All lunar rare earth elements distribution patterns resemble those found in terrestrial abyssal subalkaline basalt, but with Eu depleted by about 60 percent in all lunar samples compared to the adjacent rare earth elements. Precipitation of plagioclase and hypersthene achondritic-like minerals from a melt could account for Eu depletion and the observed distribution of rare earth elements. Abundances of Ti, Al, Ca, Na, and Mn determined by instrumental activation analysis in five core-tube soil samples indicate uniformity for Al and Mn and apparent differences (10 to 20 percent) for Ti, Ca, and Na at 7.8 and 10.5 centimeters as compared to 0to5.2 centimeter depths.     

Crystallization studies of lunar igneous rocks: crystal structure of synthetic armalcolite

Crystals of armalcolite, Mg(0.5)Fe(0.5)Ti(2)O(5), up to several millimeters in length have been grown from a glass initially having the composition of lunar rock 10017. A single-crystal x-ray study has confirmed that the crystals are isomorphous with pseudobrookite and has shown that the cations are strongly ordered, with the Ti(4+) ions occupying the 8f sites and the Fe(2+) and Mg(2+) ions randomly distributed over the 4c sites. An examination of karrooite, MgTi(2)O(5), has revealed a similar distribution of Mg(2+) and Ti(4+) ions. A reexamination of earlier x-ray and M?ssbauer data for pseudobrookite, Fe(2)TiO(5), has shown that it is more consistent with this type of ordering than with the inverse structure that has been generally assumed.