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Petrographic Descriptions |
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Petrographic Descriptions |
| Sample No.: | GRA95229 |
| Location: | Graves Nunatak |
| Dimensions (cm): | 5.0x3.0x3.5 |
| Weight (g): | 128.9 |
| Meteorite Type: | CR2 Chondrite |
Macroscopic Description: Kathleen McBride
The exterior has dull black fusion crust with polygonal fractures. The matrix is dark with numerous chondrules most of which have weathered to a yellowish color.
Thin Section (,2) Description: Brian Mason
The section shows a close packed aggregate of chondrules (up to 2 mm across) and chondrule fragments in a small amount of black matrix which contains about 10% nickel-iron (in part concentrated as rims to chondrules) and a little troilite. Chondrule types include granular olivine, olivine-pyroxene and barred olivine. Weathering is indicated by pervasive limonitic staining. Microprobe analyses show that most of the olivine is close to Mg2SiO4 in composition, with a few iron-rich grains; pyroxene composition is Fs2-4. The meteorite is tentatively clas-sified as a C2 chondrite of the Renazzo subtype, although the amount of matrix is unusually low.
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| Plane-Polarized Light | Cross-Polarized Light |
| Sample No.: | GRO95502; GRO95504; GRO95512 |
| Location: | Grosvenor Mountains |
| Dimensions (cm): | 13.0x13.5x17.0; 19.0x13.0x14.0; 11.5x7.0x8.0 |
| Weight (g): | 5362.7; 4018.3; 840.4 |
| Meteorite Type: | L3 Chondrites (estimated L3.5) |
Macroscopic Description: Kathleen McBride
All three of these ordinary chondrites have a brown/black fusion crusted exterior with chondrules/clasts visible. The interiors reveal a brownish black matrix with abundant chondrules that range in size from mm to 1 cm. All three have minor metal and some rusty areas.
Thin Section (GRO95502,2; GRO95504;2; GRO95512,2) Description: Brian Mason
The sections are so similar that a single description will suffice; the meteorites are probably paired. The sections show numerous chondrules and chondrule fragments, up to 3.2 mm across, in a black matrix containing small amounts of nickel-iron and troilite The chondrules are mainly granular and porphyritic olivine and olivine-pyroxene, with a few radiating and cryptocrystalline pyroxene. Microprobe analyses show olivine and pyroxene of variable compositions: olivine, Fa2-24, mean Fa14; pyroxene, Fs1-28. The meteorites are classified as L3 chondrites (estimated L3.5). They are very similar to GRO95505, 95544, 95545, and the possibility of pairing should be considered.
| Sample No.: | GRO95546 |
| Location: | Grosvenor Mountains |
| Dimensions (cm): | 7.0x3.0x4.0 |
| Weight (g): | 200.54 |
| Meteorite Type: | L3 Chondrite (estimated L3.8) |
Macroscopic Description: Kathleen McBride
The exterior of this ordinary chondrite has some patches of black fusion crust. Most of the fusion crust has weathered away. Iridescent oxidation halos and some evaporites are present on the exterior surface. The interior is gray with light chondrules ~ 1 mm in size. Rust is abundant especially around the edges and forms an oxidation rind. Some metal is visible.
Thin Section (,2) Description: Brian Mason
The section shows an aggregate of chondrules, chondrule fragments and silicate grains with minor amounts of nickel-iron and troilite. Minor weathering is indicated by some limonitic staining around metal grains. Microprobe analyses show olivine and pyroxene of variable compositions: olivine, Fa9-25, mean Fa19; pyroxene, Fs12-27. The meteorite is classified as an L3 chondrite (estimated L3.8).
| Sample No.: | GRO95551 |
| Location: | Grosvenor Mountains |
| Dimensions (cm): | 6.5x4.0x4.0 |
| Weight (g): | 213.389 |
| Meteorite Type: | Chondrite (Anomalous) |
| Processing Photos | |
Macroscopic Description: Kathleen McBride
The exterior of this unusual meteorite has thin patches of black fusion crust. Most of the surface has a rusty brown melted appearance with exposed clasts. The clasts are large, rounded and greenish-white with coarse crystalline textures. The interior is rusty and heavily weathered. A variety of inclusions are visible, some are black, very fine-grained and angular. There are a number of rounded objects less then 2-3 mm that could be chondrules. One large clast is greenish-yellow in color, others are rusty. This metorite was very coherent and difficult to break.
Thin Section (,2,11,13,15) Description: Brian Mason
The sections show a breccia of two types of clasts, chondritic and achondritic. The chondritic clasts range up to 15+ mm, and consist of a variety of chondrules and chondrule fragments (up to 1.8 mm across) in a matrix of nickel-iron with minor troilite. Microprobe analyses of the chondrules gave the following compositions: olivine, Fa1-2; pyroxene, Fs1, with a few more iron-rich grains. The nickel-iron contains no silicon. The achondritic clasts are up to 11 mm across and consist of highly-shocked enstatite (or clinoenstatite). GRO 95551,15 contains a fine-grained carbonaceous clast, 3.6 mm across. The meteorite is anomalous, and resembles Bencubbin (Geochim. Cosmochim. Acta, v.42, p.507, 1978) and Weatherford (Geochim, Cosmochim, Acta, v.32, p.661, 1968).
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| Plane-Polarized Light | Cross-Polarized Light |
| Sample No.: | GRO95633 |
| Location: | Grosvenor Mountains |
| Dimensions (cm): | 4.7x2.5x3.0 |
| Weight (g): | 58.10 |
| Meteorite Type: | Eucrite (brecciated) |
Macroscopic Description: Cecilia E. Satterwhite
95% of the exterior of this achondrite is covered by shiny, black fusion crust. The fusion crust appears glassy in some areas. The interior reveals a complex breccia consisting of a wide variety of clasts in a light gray matrix. The largest clasts are fine grained dark gray melts. There is one large white (plagioclase) clast and several coarse grained yellow-green mineral clasts. Some areas are mottled with black and white patches. Some oxidation is scattered in the interior but is heavier along the edges.
Thin Section (,3) Description: Brian Mason
The section shows a microbreccia of plagioclase clasts (up to 1.8 mm) and basaltic fragments in a groundmass of comminuted plagioclase and dark brown glass. A few metal grains are present, surrounded by brown limonitic staining. Plagioclase composition is fairly uniform, An91-92; pyroxene composition in a basaltic clast ranges from Wo5Fs32 to Wo2Fs57. The meteorite is a brecciated eucrite.
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| Plane-Polarized Light | Cross-Polarized Light |
| Sample No.: | PRE95401 |
| Location: | Mount Prestrud |
| Dimensions (cm): | 5.5x4.5x3.5 |
| Weight (g): | 186.53 |
| Meteorite Type: | L3 Chondrite (estimated L3.4) |
Macroscopic Description: Kathleen McBride
The exterior of this ordinary chondrite has thin weathered brown/black fusion crust, rusty in areas with some fractures present. The interior reveals a medium gray crystalline matrix with numerous light colored chondrules and irregularly shaped inclusions. The sample is rusty in areas and metal grains are present.
Thin Section (,2) Description: Brian Mason
The section shows numerous chondrules and chondrule fragments, up to 1.8 mm across, in a black matrix containing small amounts of nickel-iron and troilite. The chondrules are mainly granular and porphritic olivine and olivine-pyroxene, with a few radiating and cryptocrystalline pyroxene. Microprobe analyses show olivine and pyroxene of variable composition; olivine, Fa1-32, mean Fa14; pyroxene, Fs4-18. The meteorite is classified as an L3 chondrite (estimated L3.4).
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| Plane-Polarized Light | Cross-Polarized Light |
| Sample No.: | PRE95404 |
| Location: | Mount Prestrud |
| Dimensions (cm): | 5.0x2.0x2.0 |
| Weight (g): | 39.523 |
| Meteorite Type: | R Chondrite (Reclassifed 7/2003 - previous classification was CV3 Chondrite) |
Macroscopic Description: Kathleen McBride
Fifty percent of the exterior of this carbonaceous chondrite has dull brown/black fusion crust. It has a rough texture and polygonal fractures. The interior reveals a gray crystalline matrix with metal grains present. Light colored chondrules, mm sized, are visible in the interior.
Thin Section (,2) Description: Brian Mason
The sections shows numerous chondrules (up to 1.2mm across), chondrule fragments, irregular aggregates, and silicate grains in a black matrix which contains a moderate amount of nickel-iron and sulfide. Microprobe analyses show olivine and pyroxene of variable composition: olivine, Fa1-41; pyroxene, Fs7-21. The matrix consists largely of olivine, with composition around Fa30. The meteorite is tentatively classified as a C3 chondrite of the Vigarano subtype, but it lacks the marked olivine composition peak at Fa0-1 commonly present in C3 chondrites.
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| Plane-Polarized Light | Cross-Polarized Light |
| Sample No.: | PRE95410; PRE95411; PRE95412 |
| Location: | Mount Prestrud |
| Dimensions (cm): | 4.0x3.0x2.5; 4x2.5x2; 2.5x2.5x2 |
| Weight (g): | 41.65; 43.69; 14.63 |
| Meteorite Type: | R Chon. (Carlisle Lakes) |
Macroscopic Description: Kathleen McBride
The surface of all three of these meteorites have black fusion crust with polygonal fractures. The surfaces are pitted and vesicular. The interior is medium gray with small light clasts and chondrules visible.
Thin Section (PRE95410,2; PRE95411,2; PRE95412,2) Description: Brian Mason
The sections are so similar that a single description suffices; the meteorites are certainly paired. The sections show polycrystalline silicates clasts (up to 3 mm across), chondrules (up to 1.2 mm across) and mineral grains in a finely granular gray matrix. Nickel-iron and sulfide are present in accessory amounts. The meteorite is essentially unweathered. Microprobe analyses show olivine and pyroxene of variable composition. Olivine compositions show a prominent peak at Fa39, with a few more magnesian grains., Pyroxene is present in minor amounts, both hypersthene (Wo4Fs29) and diopside (Wo45Fs15). The meteorite is an R chondrite, very similar to PCA91002 (Meteoritics, 29, p.255, 1994).
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| Plane-Polarized Light | Cross-Polarized Light |