Geology Reference
In-Depth Information
R6 chondrite
50.405 g
Found January 20, 2005
5.0 × 3.0 × 1.75 cm
Weathering = A/B
ordinary chondrites, such as chondrule types, rare refractory inclusions,
and similar chemical compositions. There are, however, significant differ-
ences between R chondrites and ordinary chondrites, such as a much
higher proportion of matrix, more oxidized (high Ni-olivine and low
metallic FeNi contents), and enrichments in
17
o over that of ordinary
chondrites. Many R chondrites are brecciated and may originate in an
asteroid regolith.
LAP 04 ...
,2
,0
,1
Asteroid radius km
400500
LAP04840
hornblende
0
100200
300
600700
800
0
250 bars
5
500 bars
10
15
20
4000
3600
3100
2100
Wavenumber [cm
-1
]
2600
1600
1100
600
ρ
= 3 gm/cm
3
25
30
Olv
Olv
Phl
50
µ
m
Plate 36
MiNERALogy
SigNiFiCANCE
LAP 04840 is texturally heterogeneous, containing relict
chondrules up to 1 mm, isolated mineral grains 100-200
microns, and microcrystalline areas reaching 1 mm with
mafic silicate grain sizes of 5-10 microns. Shock effects
are pervasive, particularly in plagioclase. The rock con-
sists of olivine (Fa
38
), orthopyroxene (Fs
30
Wo
1
), plagio-
clase (An
7
or
3
), calcic hornblende and minor biotite
(bottom left; [241]). opaque minerals include troilite,
pentlandite, and chromite.
LAP 04840 is a one-of-a-kind meteorite: at the time it
was classified it was the only such hornblende- and bio-
tite-bearing chondrite known. its oH-bearing minerals
(middle left, arrow is oH peak; [243]), together with sili-
cate and oxide mineralogy, define pressures of 250 to 500
bars (could be as deep as 25 km, right; [241]) and high
oxygen fugacities, above the FMQ oxygen buffer.
References [240-244]
