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66 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
throughout, and chondrules are few and poorly
defined. These features are demonstrated by a lowpower
photomicrograph of a polished surface (Figure
4). An unusual feature of broken surfaces of
this meteorite is the complete absence of any rusting
around the metal particles, despite exposure to the
atmosphere for many years; this implies the absence
of lawrencite. Only two thin sulfide veins were
observed on a 170 cm 2 broken surface. One crossed
the specimen for 14 cm, while the other was only
3 cm long.
Thin sections under the microscope show a
granular aggregate of olivine, orthopyroxene, and
opaque minerals (Figure 5). The original chondritic
texture has almost disappeared. Chondrules are
recognizable by their vaguely circular form and
their usually coarser grain size than the surrounding
matrix. The fusion crust shows three welldeveloped
zones. The outermost zone is very thin,
averaging about 0.05 mm, and consists of black
opaque glass, the opacity appearing to be largely
due to finely dispersed magnitite or magnesioferrite.
The next zone averages 0.1 mm, is transparent, and
consists largely of granular olivine and pyroxene
like that in the body of the meteorite; it also
contains occasional pools of isotropic, fused plagioclase.
The innermost zone is considerably thicker,
averaging 0.3 mm; it is black and opaque in transmitted
light, but in reflected light it is seen to
consist of the same minerals as the body of the
meteorite, but impregnated with a network of
minute troilite veinlets following grain boundaries,
cleavages, and fractures.
Reflected light examination of polished surfaces
revealed the presence of troilite, kamacite, taenite,
chromite, and trace amounts of copper. Troilite is
mainly present in isolated coarse-grained patches,
but also occurs in association with kamacite and/or
taenite. A variety of metal structures is seen on
etched surfaces. Large clear kamacite areas are
present, as are polycrystalline kamacite masses.
Some kamacite areas contain silicate inclusions and
several contain small troilites. Taenite inclusions
generally are smaller than kamacite and have complex
structures. They appear to be pearlitic and
occasionally include small grains of troilite. Small
areas of copper were observed twice within kamacite
and in association with small grains of troilite,
and once at a grain boundary within a large area
of troilite. Several areas that suggest shock melting
of troilite or kamacite were observed, but these are
comparatively rare. The overall impression is one
of a compact rock with clean and well-defined
crystal boundaries.
As mentioned above, the principal minerals are
olivine and pyroxene. Other characteristic minerals
are nickel-iron, plagioclase, feldspar, and troilite.
Minor minerals include chromite and a phosphate
mineral (apatite and/or whitlockite) and copper is
present as a trace mineral. Ramdohr (1973:89) has
recorded the following opaque minerals: kamacite,
taenite, plessite, copper, troilite, chalcopyrrhotite
(trace), mackinawite, and chromite. Our notes on
some of the minerals follow.
Olivine: The refractive indices are a = 1.682,
y = 1.720, indicating a content of 25 mole percent
of the Fe2SiO4 component, according to the determinative
curve of Poldervaart (1950). Microprobe
analyses show 24.6 mole percent Fe2SiO4 in the olivine.
The chemical analysis of the acid-soluble
nonmagnetic fraction (Table 1), essentially olivine
with troilite and a little phosphate, indicates 26
mole percent Fe2SiO4.
Orthopyroxene: The refractive indices are a —
1.678, y = 1.689, indicating a content of 21 mole
percent of the FeSiO3 component, according to the
determinative curve of Kuno (1954). Microprobe
analyses show the Fe/Fe + Mg mole percentage of
the orthopyroxene to be 22.4, with a content of
0.85% CaO in this material. The chemical analysis
of the acid-insoluble nonmagnetic fraction (Table
1), essentially orthopyroxene and plagioclase, shows
an Fe/Fe+Mg mole percentage of 23. In terms of
the conventional subdivision of meteoritic pyroxene,
this falls in the compositional range of hypersthene.
Diopside: An x-ray diffractogram of the acidinsoluble
fraction shows a low-intensity peak corresponding
to diopside. This mineral was not
certainly identified microscopically or with the
microprobe, although some turbid and fine-grained
material is probably clinopyroxene.
Plagioclase: The plagioclase feldspar is finegrained,
granular, untwinned, and interstitial to
the other minerals. Microprobe analyses give a
composition of An9, with a K2O content of 1.11%.
Chromite: Bunch, Keil, and Snetsinger (1967,
table 2) give the following microprobe analysis of
Harleton chromite: Cr2O3, 56.0; A12O3, 5.1; V2O3,
0.73; TiO2, 2.88; FeO, 33.4; MgO, 2.11; MnO, 0.57.