A large (>4.5 x 7 x 4 mm), igneous-textured clast in the Bovedy (L3) c
hondrite is notable for its high bulk SiO2 content (almost-equal-to 57
.5 wt%). The clast consists of normally zoned orthopyroxene (83.8 vol
%), tridymite (6.2 %), an intergrowth of feldspar (5.8 %) and sodic gl
ass (3.1 %), pigeonite (1.0 %), and small amounts of chromite (0.2 %),
augite, and Fe,Ni-metal; it is best described as a silica-rich orthop
yroxenite. The oxygen-isotopic composition of the clast is similar, bu
t not identical, to Bovedy and other ordinary chondrites. The clast ha
s a superchondritic Si/Mg ratio, but has Mg/(Mg + Fe) and Fe/Mn ratios
that are similar to ordinary chondrite silicate. The closest chemical
analogues to the clast are radial-pyroxene chondrules, diogenites, py
roxene-silica objects in ordinary chondrites, and silicates in the IIE
iron meteorite Weekeroo Station. The clast crystallized from a silice
ous melt that cooled fast enough to prevent complete attainment of equ
ilibrium but slow enough to allow nearly complete crystallization. The
texture, form, size and composition of the clast suggest that it is a
n igneous differentiate from an asteroid or planetesimal that formed i
n the vicinity of ordinary chondrites. The melt probably cooled in the
near-surface region of the parent object. It appears that in the sour
ce region of the clast, metallic and silicate partial melt were largel
y-to-completely lost during a relatively low degree of melting, and th
at during a higher degree of melting, olivine and low-Ca pyroxene sepa
rated from the remaining liquid, which ultimately solidified to form t
he clast. While these fractionation steps could not have all occurred
at the same temperature, they could have been accomplished in a single
melting episode, possibly as a result of heating by radionuclides or
by electromagnetic induction. Fractionated magmas can also account for
other Si-rich objects in chondrites.