Geology Reference
In-Depth Information
IIAB iron (coarse octahedrite)
10,000, 2689.4 g
Found December 19, 2000
1.0 × 0.8 × 0.5 cm
Weathering = B
The iiAB irons include hexahedrites and octahedrites, and are part of the
third largest iron meteorite group. The iiAB iron meteorites are thought
to have formed during the crystallization of an S- and P-bearing metallic
core, at the center of a differentiated asteroid. These deep-formed asteroid
samples thus offer a glimpse into differentiation processes in the early
solar system.
DRP 00200,0
DRP 00201
5 cm
Plate 78
MiNERALogy
SigNiFiCANCE
From a cut surface, DRP 00200 resembles typical mem-
bers of the Derrick Peak iron shower (bottom, [817]).
only a thin layer of corrosion is found on the surface, and
neither fusion crust nor heat-altered zone is found.
Structurally, they are coarsest octahedrites with large
areas of swathing kamacite enclosing elongate, skeletal
schreibersite crystals and centimeter-sized round troilite
inclusions.
The Derrick Peak irons were found in 1978 and 2000 field
seasons and comprise 27 members with a total mass of
408.4 kg. This pairing group has helped to define the
sizable group of iron meteorites that constitutes the iiAB
irons. The group has the largest known range in ir concen-
trations (a factor of 4000) and slopes that are steeply nega-
tive on plots of ir versus Au or As (or Ni). iiAB appears
to have had the highest S contents of any magmatic group
of iron meteorites, consistent with its high contents of
other volatile siderophiles, particularly ga and ge.
References [816-817]
