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NUMBER 19 77 FIGURE 4.—Photomicrograph of thin section of the hypersthene chondrite. Mabwe-Khoywa. The chondritic main mass is L3 or L4, olivines in most chondrules and fragments have approximately Fa24; one chondrule indicated by arrow and shown in Figure 5 has Fas.u. In the achondritic fragment (right), the small olivines are in the range Fa,i.14, some of the larger Fa2o.23, while the interstitial glass is albitic with excess normative quartz and corundum. Length of section, 12.5 mm. The olivine with highest iron content was found in a lithic fragment (possibly a chondrule). The crystal has 25.5% FeO (Fa28) in the center and 24% at the edge. Adjacent glass is again mostly albitic but has a substantial excess of normative corundum along with some iron and magnesium. It is remarkable that Mabwe-Khoywa in spite of all this diversity of components has a bulk composition almost identical to the other L-chondrites. Indeed, even the abundances and average compositions of the phases are close. Mabwe-Khoywa is apparently the product of multiple impacts, and after the first, or first few, impacts its chemistry was not significantly altered. Olivine: Fs24.s Pyroxene: Wo Plagioclase: O En78 Fs2i 4 Ab^ AnJ7 MIRZAPUR It has been classified as a veined intermediate chondrite (Cia) and L6; we prefer L5 (towards L4) because our specimen is relatively unconsolidated and the thin sections show well-delineated chon-
78 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES FIGURE 5.—An Mg-rich olivine and pyroxene chondrule (shown by arrow in Figure 4), is lined with nickel-iron and troilite, black. It is intergrown with matrix (lower right) and with a fragment of a barred "equilibrated" olivine (Fa^) chondrule (lower left), which is part of a fragment of preexisting chondrite (shown under arrow in Figure 4). Length of section, 0.6 mm. drules (Figure 6), some with Si-Al enriched and only partly devitrified glass. This glass has approximately 66% SiO2, 21% A12O3, and 8% soda; the normative composition is again almost albitic with some quartz and minor corundum and pyroxene. Shock alterations, including fracturing wavy extinction and veining (Fredriksson, et al., 1964), are abundant and the glass may be impact-produced; however, it would hardly be in equilibrium with olivine-pyroxene at metamorphic temperatures of 800° to 1000° C. Olivine: Fa^.o Pyroxene: Woj s En77 Fs^ Plagioclase: Or5 Ab7S AnJ7 SEGOWLIE Segowlie perfectly fits the definitions for a crys- talline chondrite and almost as well for the L6 group. The photomicrograph in Figure 7 shows individual patches with equigranular, recrystallized structure, identical to that in the H-chondrite Andura (Fredriksson, et al., 1975). However, the grain size varies grossly between the different parts, i.e., the stone is still a breccia. Thus it seems unlikely even in this case that the structure is due to simple metamorphic recrystallization. Some parts (Figure 8) also show rather well-delineated chondrules, i.e., a structure more like L5. Olivine: Fa^., Pyroxene: Wo, En78 Fs22; W044 Plagioclase: Or5 Ab77 An18 SULTANPUR Walker, 1924; Coulson, 1940 Sultanpur has been classified as a black chondrite and an L6, but both designations are somewhat questionable. It is more a black chondrite than Atarra, but not in the same sense as shock products like Farmington and McKinney (Fredriksson, et al., 1964; Heymann, 1967). Sultanpur seems rather to be close to a brecciated (and veined) gray chondrite. The grain size is much finer and the chondrules better defined than in the L6 Segowlie; thus Sultanpur could probably also be an L5, particularly because the plagioclase does not occur as clear, well-defined grains. Evidence of shock effects, e.g., fracturing and undulatory extinction, in both olivine and pyroxene are common, however. Discussion Bulk and phase compositions, as well as phase abundances (Tables 1, 2), clearly show the close relation among these eight meteorites in spite of their different appearances and classifications. Essentially only the contents of nickel-iron and troilite vary significantly (Table 3), while the silicate fractions are chemically almost identical even in the obviously fragmentary Mabwe-Khoywa. The silicate fraction compositions in Table 4 were obtained by deducting metal, troilite, Fe for ilmenite and chromite, and Ca for apatite from the bulk analysis. While normative and modal amounts of pyroxene are close, both olivine and plagioclase are higher in the norm, which must be compensated for by
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SMITHSONIAN CONTRIBUTIONS TO THE EA
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Contents MINERALOGY COMPOSITION OF
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Constituent SiO TiO Al 0 fl 2 3 Cr
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PER CENT CBLCIUM FIGURE 3.—The ca
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Constituent TiO,, 2 2 3 FeO* MnO Mg
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20 Cfl 40 .60 SMITHSONIAN CONTRIBUT
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12 SMITHSONIAN CONTRIBUTIONS TO THE
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14 20 SMITHSONIAN CONTRIBUTIONS TO
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16 Constituent Si0 2 TiO2 A12O3 Cr
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18 20 40 £0 SMITHSONIAN CONTRIBUTI
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20 40 20 SMITHSONIAN CONTRIBUTIONS
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Abyssal Basaltic Glasses as Indicat
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24 Electron-M icroprobe Analysis An
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