Antarctic Meteorite Newsletter, Volume 27, No. 3 - August 2004
Volume 27, No. 3 - August 2004

Petrographic Descriptions             Go to Pet. Desc. Page 1 of 2

Sample No.: LAP 03569
Location: LaPaz Ice Field
Field No.: 16919
Dimensions (cm):   10.5x8.0x7.0
Weight (g): 813.7
Meteorite Type: Diogenite
    LAP03569 LAP03569

Macroscopic Description: Kathleen McBride
75% of the exterior is covered with chocolate brown fusion crust. The crust has a slight sheen with polygonal fractures. The exposed matrix is tan and has weathered, large green inclusions. The interior matrix is light gray with olive green angular inclusions.

Thin Section (,2) Description: Tim McCoy, Linda Welzenbach
LAP 03569 - Cross-Polarized Light LAP 03569 - Plane-Polarized Light
Cross-Polarized Light Plane-Polarized Light
The section shows a groundmass of coarse (up to 3 mm) comminuted pyroxene, with lesser olivine. Orthopyroxene has a composition of Fs22Wo2 and an Fe/Mn ratio of ~28; olivine is Fa27. The meteorite is a diogenite and is compositionally similar to LAP 91900 and LAP 02216. It could be paired with the latter, although it contains much more abundant olivine.


Sample No.: LAP 03593; LAP 03605; LAP 03631
Location: LaPaz Icefield
Field No.: 16731; 16721; 16715
Dimensions (cm):   8.0x6.0x5.5
9.5x5.5x4.5
7.5x3.5x3.5
Weight (g): 657.5; 582.8; 164.9
Meteorite Type: Iron (Sulfide-Rich)
   
LAP03593 LAP03593
LAP03605 and LAP03631  

Macroscopic Description: Tim McCoy, Lisa Collins
These meteorites exhibit a common external appearance. They have a knobby surface with numerous rounded protrusions up to 1 cm across intermixed with indentations containing a macroscopically jointed mineral.

Microscopic Description: Tim McCoy, Linda Welzenbach
These meteorites were examined from a cut surface of LAP 03593, which displays a sub equal mixture of metal and sulfide with trace amounts of schreibersite and silicates or graphite. The troilite occurs as irregular blobs up to 3 cm in length each of which is composed of multiple troilite crystals 3-5 mm across and exhibit prominent parallel jointing. The metal contains swathing kamacite rims typically 1 mm thick and short irregular bars of kamacite approximately < 0.5 mm. A heat altered α2 structure extends up to 5 mm from the exterior weathered surface, and a highly altered fusion crust may be preserved in some places. The meteorites are similar to the IAB iron Pitts and the ungrouped iron Soroti, but exhibit coarser kamacite band widths than either, and lack the abundant silicates seen in Pitts.


Sample No.: LAP 03630
Location: LaPaz Ice Field
Field No.: 16049
Dimensions (cm):   5.5x4.0x3.5
Weight (g): 175.672
Meteorite Type: Diogenite
    LAP03630 LAP03630

Macroscopic Description: Kathleen McBride
The exterior has small patches of chocolate brown crust (<10%) visible on the exterior. Areas without fusion crust show a tan matrix with green clasts visible. The interior matrix is light gray with olive green, angular inclusions.

Thin Section (,2) Description: Tim McCoy, Linda Welzenbach
The section is dominated by orthopyroxene, with individual grains reaching over 5 mm. The majority of the section consists of smaller (1 mm), equant grains which commonly intersect at 120º triple junctions. Orthopyroxene has a composition of Fs24Wo2 and an Fe/Mn ratio of ~28. The meteorite is a diogenite, although its texture is unusual.


LAP 03630 - Cross-Polarized Light LAP 03630 - Plane-Polarized Light LAP 03630 - Cross-Polarized Light LAP 03630 - Plane-Polarized Light
LAP 03630
Cross-Polarized Light
LAP 03630
Plane-Polarized Light
LAP 03630
Cross-Polarized Light
LAP 03630
Plane-Polarized Light


Sample No.: LAP 03632
Location: LaPaz Ice Field
Field No.: 16823
Dimensions (cm):   5.5x3.5x3.0
Weight (g): 92.566
Meteorite Type: Lunar-Basalt
    LAP03632 LAP03632

Macroscopic Description: Kathleen McBride
~75% of the exterior has shiny black fusion crust. The interior is pinkish-tan with white linear minerals and glass veins. This sample is paired with the LAP samples from the '02 season.

Thin Section (,2) Description: Tim McCoy, Linda Welzenbach
The section consists of a coarse-grained unbrecciated basalt with elongate pyroxene (up to 0.5 mm) and plagioclase laths (up to 1 mm) (~60:40 px:plag), rare phenocrysts of olivine (up to 1 mm) and interstitial oxides and late-stage mesostasis. Shock effects include undulatory extinction in pyroxene and shock melt veins and pockets. Microprobe analyses reveal pigeonite to augite of Fs27-52Wo12-33, plagioclase is An87Or0-1 and a single olivine phenocryst is Fa32-99. The Fe/Mn ratio in the pyroxenes averages ~60. The meteorite is a lunar olivine-bearing basalt and is almost certainly paired with LAP 02205, LAP 02226, LAP 02224 and LAP 02436.


LAP 03632 - Cross-Polarized Light LAP 03632 - Plane-Polarized Light LAP 03632 - Cross-Polarized Light LAP 03632 - Plane-Polarized Light
LAP 03632
Cross-Polarized Light
LAP 03632
Plane-Polarized Light
LAP 03632
Cross-Polarized Light
LAP 03632
Plane-Polarized Light


Sample No.: LAP 03719
Location: LaPaz Ice Field
Field No.: 16255
Dimensions (cm):   5.5x4.0x2.5
Weight (g): 62.021
Meteorite Type: Aubrite (Anomalous)
    LAP03719

Macroscopic Description: Kathleen McBride
The exterior has 40% fusion crust, gray-brown in color. The interior is a white matrix with brown circular to oval shaped inclusions. The matrix is stained brown and has lots of rust/weathering.

Thin Section (,2) Description: Tim McCoy, Linda Welzenbach
The section is an unbrecciated rock consisting of essentially FeO-free enstatite, diopside and olivine with minor metal, troilite, daubreelite and alabandite. Enstatites reach 1 cm in maximum dimension and contacts between enstatite grains are often interfingering. Blebby diopside exsolution occurs within enstatite and at enstatite-enstatite grain boundaries. Olivine, which occupies ~20% of the section, reaches 3 mm. Although the pyroxene textures are reminiscent of some aubrite clasts, the unbrecciated nature, texture and olivine abundance in this aubrite are unique.


LAP 03719 - Cross-Polarized Light LAP 03719 - Plane-Polarized Light LAP 03719 - Cross-Polarized Light LAP 03719 - Cross-Polarized Light
LAP 03719
Cross-Polarized Light
LAP 03719
Plane-Polarized Light
LAP 03719
Cross-Polarized Light
LAP 03719
Cross-Polarized Light


Sample No.: LAP 03780; LAP 031269;               LAP 031372
Location: LaPaz Icefield
Field No.: 16745; 16191; 16719
Dimensions (cm):   3.5x2.5 x 2.0
2.5x2.5x2.0
3.0x2.0x2.5
Weight (g): 21.807; 12.930; 17.613
Meteorite Type: Aubrite
   
LAP03780 LAP031269
LAP031372  

Macroscopic Description: Kathleen McBride
The exteriors are white without any fusion crust. The interiors are white matrix with brown circular to oval shaped inclusions.

Thin Section (,2) Description: Tim McCoy, Linda Welzenbach
The sections consist of an aggregate of coarse (up to 5 mm), heavily shocked enstatite grains with minor to trace abundances of diopside, metal, troilite, alabandite, and daubreelite. Silicates are essentially FeO-free enstatite (Fs0Wo1) and diopside (Fs0Wo43). The meteorites are aubrites and may be paired with LAP 02233. They were found over a range of 1.5 km.


LAP 03780 - Cross-Polarized Light LAP 03780 - Plane-Polarized Light LAP 031269 - Cross-Polarized Light
LAP 03780
Cross-Polarized Light
LAP 03780
Plane-Polarized Light
LAP 031269
Cross-Polarized Light
LAP 031269 - Plane-Polarized Light LAP 031372 - Cross-Polarized Light LAP 031372 - Plane-Polarized Light
LAP 031269
Plane-Polarized Light
LAP 031372
Cross-Polarized Light
LAP 031372
Plane-Polarized Light


Sample No.: LAP 03782
Location: LaPaz Ice Field
Field No.: 16082
Dimensions (cm):   2.5x2.5x1.75
Weight (g): 22.269
Meteorite Type: Eucrite (Unbrecciated)
LAP03782 LAP03782

Macroscopic Description: Kathleen McBride
The exterior of this eucrite has about 40% thin, black, shiny fusion crust. The interior has a dense crystalline matrix with minor rust and is very hard.

Thin Section (,2) Description: Tim McCoy, Linda Welzenbach
LAP 03782 - Cross-Polarized Light LAP 03782 - Plane-Polarized Light
Cross-Polarized Light Plane-Polarized Light
This meteorite exhibits a granoblastic texture, with pyroxenes reaching 1.5 mm and plagioclase 1.0 mm, although most grains are smaller. Pyroxenes are exsolved on the scale of 1-20 microns, with orthopyroxene (Fs58Wo4), with lamellae of augite (Fs30Wo37), and plagioclase (An90Or0.2). The Fe/Mn ratio of the pyroxene is ~30. Staining by hydrated iron oxides is pervasive. The meteorite is an unbrecciated eucrite.


Sample No.: LAP 03979; LAP 031381
Location: LaPaz Icefield
Field No.: 16489; 16628
Dimensions (cm):   1.5x1.25x0.75
1.5x1.25x0.75
Weight (g): 2.406; 1.890
Meteorite Type: Diogenite (Olivine)
   
LAP03979 LAP03979
LAP031381 LAP031381

Macroscopic Description: Kathleen McBride
95% of the exterior is covered with brown/black fusion crust with small shiny patches. The rusty, granular interior has mm sized black inclusions and green mineral grains that are up to 2 mm in size.

Thin Section (,2) Description: Tim McCoy, Linda Welzenbach
These two small sections are unbrecciated rocks dominated by orthopyroxene (Fs25Wo3), olivine (Fa30) and plagioclase (An80-85Or1). Most grains are less than 0.5 mm in diameter, although a single pyroxene in 031381 reaches 4 mm. The meteorites are unbrecciated olivine diogenites.


LAP 03979 - Cross-Polarized Light LAP 03979 - Plane-Polarized Light LAP 031381 - Cross-Polarized Light
LAP 03979
Cross-Polarized Light
LAP 03979
Plane-Polarized Light
LAP 031381
Cross-Polarized Light
LAP 031381 - Plane-Polarized Light LAP 031381 - Cross-Polarized Light LAP 031381 - Plane-Polarized Light
LAP 031381
Plane-Polarized Light
LAP 031381
Cross-Polarized Light
LAP 031381
Plane-Polarized Light


Sample No.: MIL 03346
Location: Miller Range
Field No.: 13205
Dimensions (cm):   10.0x6.0x5.5
Weight (g): 715.200
Meteorite Type: Nakhlite
    MIL03346 MIL03346

Macroscopic Description: Kathleen McBride
60% of the exterior is covered with black "wrinkled" appearing fusion crust. The areas without fusion crust are a black crystalline material with vugs. The binocular microscopic view of the exterior surface appears melted or fused together. The interior reveals a coarse grained, dark green to blackish crystalline matrix with a granular texture. This nakhlite is unbrecciated and homogeneous with interlocking grains and minor rust.

Thin Section (,2) Description: Tim McCoy, Cari Corrigan, Linda Welzenbach
MIL 03346 - Cross-Polarized Light MIL 03346 - Plane-Polarized Light
Cross-Polarized Light Plane-Polarized Light
The section is dominated by lathy to equant clinopyroxene that reaches 2 mm in maximum dimension. Mesostasis occupies approximately 20% of the rock and contains skeletal iron-titanium oxides. Clinopyroxenes have core compositions of Fs21 Wo40 with rims reaching Fs49 Wo34. Olivine was not observed. The meteorite is a nakhlite. Its pyroxenes are compositionally similar to Lafayette, but it is richer in mesostasis and unusual for nakhlites in lacking olivine.


Sample No.: MIL 03356
Location: Miller Range
Field No.: 13970
Dimensions (cm):   7.5x4.5x3.0
Weight (g): 443.5
Meteorite Type: Iron-IVA
    MIL03356

Macroscopic Description: Tim McCoy, Lisa Collins
This slipper-shaped meteorite has a smooth exterior surface partially (30-50%) covered by fusion crust which exhibits prominent flow lines. Prominent fracturing, which follows the Widmänstatten structure, extends to the interior along the end opposite the nose. An interesting feature is the presence of two holes, about 1 mm in diameter and of depth equal to or greater than the diameter, one of which contains a single euhedral metal crystal.

Microscopic Description: Tim McCoy, Linda Welzenbach
The meteorite was examined from a cut and etched surface, which bisected the larger end or nose of the specimen. The surface exhibits prominent kamacite lamellae (L/W ~20) with bandwidths less than 0.2-0.3 mm set in approximately 40-50% plessite fields. Rare, very small troilite inclusions, up to 1mm are present. An elongate needle, 2.5 mm long, of chromite(?) is also present. The meteorite appears to have been extensively shocked and exhibits α2 structure throughout the meteorite and prominent Neumann bands in many of the kamacite lamellae. A thin fusion crust is preserved over much of the surface, and a heat altered zone approximately 0.5 mm thick underlies that fusion crust. The meteorite is similar to the IVA iron Duchesne.


Sample No.: MIL 03369
Location: Miller Range
Field No.: 13972
Dimensions (cm):   5.0x2.5x2.0
Weight (g): 119.963
Meteorite Type: Iron-IIIC
    MIL03369 MIL03369

Macroscopic Description: Tim McCoy, Lisa Collins
This lozenge-shaped meteorite has a rounded exterior peppered with 3 mm rust halos, and has a single comma shaped indentation. Most of the surface is relatively smooth, while the botom face shows a subtle relief of the Widmänstatten pattern.

Microscopic Description: Tim McCoy, Linda Welzenbach
The meteorite was examined from a cut and etched surface, which bisects the long axis of the specimen. The cut surface exhibits prominent skeletal kamacite lamellae (L/W ~50) with bandwidths less than 0.2-0.5 mm set in approximately 40-50% plessite fields of both comb (~10%) and martensite (30-40%). The kamacite typically contain minute lathes of schreibersite crystals arrayed along the central long axis. The meteorite exhibits α2 structure throughout the prominent fissures in many of the kamacite lamellae. A thin fusion crust is preserved over some parts, and a heat altered zone approximately 0.5 mm thick underlies that fusion crust. The meteorite is similar to the IIIC iron Carlton, although appears to be more shock altered than Carlton.



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