Geology Reference
In-Depth Information
(a)
(b)
MAC 88136, 37
Mg
-
Ca
-
Al
MAC 88136, 37
Fe
-
Ni
-
S
En
En
En
Schreib
Graph
FeNi
500
μ
m
Troil
+Daub
Schreib
100
μ
m
(c)
(d)
LEW 87223,11
ALH 81189, 3
Mg
-
Ca
-
Al
1 mm
500
μ
m
Mg
-
Ca
-
Al
X-ray map
Figure 4.5.
(a) A Mg, Ca, Al composite (red, green, blue) x-ray image of the MAC 88136, 37 EL3 chondrite. The section contains
chondrules, approximately 500 µm in size, and metal nodules (black), which are slightly smaller, at about 400 µm. The red color of the
image illustrates the Mg-rich compositions of the silicates, which are mainly near-endmember enstatite. Small areas of brighter red
are less common forsterite grains. (b) A Fe, Ni, S (red, green, blue) composite image of a metal nodule in MAC 88136. The image
shows FeNi metal in red, schreibersite in green, and troilite and daubreelite in purple and blue, respectively. Enstatite (black) occurs
as euhedral crystals enclosed within and at the edges of the metal. (c) A Mg, Ca, Al (red, green, blue) composite image of ALH 81189,
3. ALH 81189 is a primitive EH3 chondrite with numerous chondrules (up to 500 µm in size) with sharp boundaries. The brightest
reds are olivine grains, which are fairly common and suggest that ALH 81189 is a primitive EH3 chondrite. (d) A Mg, Ca, Al (red,
green, blue) composite image of LEW 87223, 11 showing enstatite-rich chondrules (red) and several Al-rich chondrules (blue).
impact melting and possibly injection of metal into pore
spaces in a loosely consolidated regolith [
Van Nierkirk
et al
, 2009;
Van Nierkirk and Keil
, 2011]. Alternatively,
they have been interpreted to form from fractional con-
densation from the early solar gas [
Weisberg et al.
, 1997].
In a reducing solar nebula with a C/O ratio of ≥1, Fe metal
condenses at ~1375 K and olivine, diopside, and enstatite
condense at 1100, 1050, and 950 K, respectively [e.g.,
Larimer and Bartholomay
, 1979;
Saxena and Eriksson
,
1985;
Ebel
, 2006]. Thus, from 1375 to 1100 K, metal may
exist independently of silicates. Aggregates of condensates
in this T range would be metal-rich. Metal-rich dust
