CRYSTAL HABIT of IRON in LUNAR BRECCIAS. US Clanton, DS Mckay and RB Laughon, NASA Manned Spacecraft Center, Houston, TX

CRYSTAL HABIT OF IRON IN LUNAR BRECCIAS. U.S. Clanton, D.S. McKay and R.B. Laughon, NASA Manned Spacecraft Center, Houston, TX, and G.H. Ladle, Lockheed El ectronics Company, Houston, TX. Samples 15401 and 15402, soil from the green boulder on the Apennine Front at Station 6a, contain fragments of highly rnetamorpllosed or recrystallized breccias somewhat similar to those previously reported1. Some of these fragments contain euhedral crystals of iron growing on plagioclase and pyroxene crystals (Fig. 1) . A1 though our investigation included 30 horizons from the deep drill core (1 5001 -1 5006), samples 15401 and 15402 appear to be unique. Individual fragments with iron crystals are rare but when present the crystals usually occur in abundance. One breccia fragment from 15402 had an ex- ceptionally high concentration of iron crystals and was used to obtain crystal size statistics. A 1500X mosaic was made of a 0.57 mm2 area with the highest crystal concentration. The maximum projected length, i.e. longest dimension on the photograph, was measured on 477 iron crystals. The longest dimension recorded was 17pm; the smallest about lum. The mean crystal size was 6.6pm with an apparently normal distribution and a standard deviation of 2.0pm. Based on selected stereographic photography of some crystals , the actual length along crystallographic axis ranged from about 10pm to less than lum. Based on crystal habit, three populations have been recognized. In the first group the trapezohedron {hll ) predominates and the cube (100) faces are smaller (Figs. 2 & 3). Rare crystals have been photographed that display two values for {hll 1 and a second set of trapezohedron faces are present. The second group of crystals has the cube (100) as tile dominant form; the trapezohedron {hll and tetrahexahedron {hkO) faces are smal ler and about equally developed (Figs. 3, 4 & 5). This group of crystals often shows four or five values {hll and has four or five sets of trapezohedron faces. The tetrahexahedron faces are covered with striations, or more correctly oscillatory combinations (Fig. 6). Each striation is formed by two narrow planes that correspond in position to faces of other crystal forms. This grooved surface is formed by the continual osci 11 ation of the tetrahexahedron, trapezohedron and/or hexoctahedron forms. The dominant habit of the third group is the octahedron {111} with smal ler but equally we1 l developed cube (100) and dodecahedron {110) faces (Figs. 7 & 3). These different crystal habits may be the result of growth rate, trace elements or environment. Compositional ly the crystals in groups one and two are pure Fe; Ni, P, Co and S if present are less than .5%. The crystal shown in Fig. 8 has an uneven coating of iron sulphide. The euhedral crystals, the abundant growth steps, and the open network of substrate crystals clearly support the concent of vapor-phase crystallization1. Iron has been mobilized and redistributed in a vapor phase to form euhedral crystals in the recrystallized breccias that were formed by the thermal meta- morphism of massive ejecta blankets. Investigations of Apollo 16 samples cur- rently in progress also show iron crystals in some vuggy breccia fragments. REFERENCES (1 ) McKAY D.S., CLANTON U.S. , MORRISON D.A. and LADLE G.H. (1 972) in Proc. Third Lunar Sci. Conf., Geochim. Cosmochim. Acta Suppl . 3, V. 1, 739-752. 0 Lunar and Planetary Institute Provided by the NASA Astrophysics Data System CRYSTAL ~~ OF IRON IN LUNAR BRECCIAS FIGURE CAPTIONS Fig. 1 - SEM photograpt1 of a vuggy recrystallized breccia. Euhedral crystals of iron sit on a substrate of plagioclase and yroxene crystals; the porosity extends we1 1 into the fragment (1 5402 7 . Fig. 2 - SEN photograph of three euhedral iron crystals; the dominant crystal form is the trapezohedron, the cube faces are smaller (15402). Fig. 3 - Drawing showing modifications and combinations of cube, tetrahexahedron and trapezohedron forms. Fig. 4 - SEM photograph of an iron crystal; the dominant crystal form is the cube, the trapezohedron and tetrahexahedron faces are small er. Five values for {hll) occur on this crystal; there are five sets of trapezohedron faces. The substrate is a pyroxene fragment; the bunched growth 1 ines form 200 A" "growth steps" (1 5402). Fig. 5 - SEM photograph of an iron crystal on a pyroxene substrate. The dominant crystal form is the cube; the trapezotiedron and tetrahexahedron faces are smaller but equally well developed. Four values for {hll) occur on this crystal ; there are four sets of trapezohedron faces. The iron crystal appears to have -formed later than the growth steps on the pyroxene substrate (1 5402). Fig. 6 - SEM photograph of an iron crystal. The striation are oscillatory combinations formed by two narrow planes that correspond in position to faces of other crystal forms. The striations are observed only on the tetrahexahedron faces (1 5402) . Fig. 7 - Drawing showing modifications and combinations of octahedron, cube and dodecahedron forms. Fig. 8 - SEM photograph of an iron(?) crystal coated with iron sulfide, pre- sumably troil ite. The dominant crystal form is the octahedron; the cube and dodecahedron faces are smaller and 1ess we1 1 developed. This crystal sits on a "glazed" or "wetted" substrate. The glaze forms a coating that covers details of the previous surface (15402). 0 Lunar and Planetary Institute Provided by the NASA Astrophysics Data System CRYSTAL HABIT OF LRON IN LUNAR BRECCIAS U. S. Clanton et al. 0 Lunar and Planetary Institute Provided by the NASA Astrophysics Data System .

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