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Column: Micro Visions

NWA 4540 CO3.5

May 1, 2013

NWA 4540 CO3.5

CO3s, carbonaceous chondrites of the Ornans type, contain the smallest chondrules of any of the major chondrite types. Still, chondrule sizes vary among CO3s. And within this CO3 there is a variety of chondrule sizes and a great variety of chondrule types and other matter. It is good to be observant when scanning a thin [...]

Column: Micro Visions

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Tissint Martian Meteorite

March 1, 2013

Tissint Martian Meteorite

Tissint is the fifth witnessed Martian meteorite fall.  It is a Shergottite.  Many pieces totaling over 7 kg fell east of Tata, Morocco about 2 AM, July 18, 2011.  The stones have a shiny black fusion crust which is glossier over olivine macrocrysts.  Olivine macrocrysts and microphenocrysts are held in a finer groundmass of pyroxene, [...]

Column: Micro Visions

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Axtell CV3

January 1, 2013

Axtell CV3

A 6.2 kg stone was found in 1943 by a man cultivating a cotton field three miles south of Axtell, Texas. The family kept it until 1993 when it was bought by Blaine Reed and distributed. Except for some coloration from terrestrial weathering, it appears very similar to Allende. Close study shows that they are [...]

Column: Micro Visions

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Dellen Tagamite Sweden

November 1, 2012

Dellen Tagamite Sweden

Dellen Crater is a roundish lake system in central Sweden near the east coast 180 miles north of Stockholm. It is about 11 miles across. The impact that formed it occurred 89.0 ± 2.7 million years ago. Some of the impact rock from the site is called tagamite. It is a term that was introduced [...]

Column: Micro Visions

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CK Chondrites

September 1, 2012

CK Chondrites

CK chondrites, Karoondites, contain objects that hint at the processes that produced the rocks we have in our collections. Here are a few.                        

Column: Micro Visions

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NWA 5930 CV3

August 1, 2012

NWA 5930 CV3

NWA 5930 CV3 is interesting for the variety of chondrules, including non-textbook chondrules, it contains. Some are misshapen, several are rather large and relict grains are common. The textural contrasts are remarkable.

Column: Micro Visions

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Coolidge C4 – ung

July 1, 2012

Coolidge C4 – ung

The namesake of the Coolidge grouplet of meteorites was found in 1937 and has been classified H4, CV4 and C3.8-ung. Studies distinguish Coolidge from CK chondrites (which contain type 4 examples) and from CV chondrites. Some chondrules are large and layered from repeated accretion and heating in the solar nebula.           [...]

Column: Micro Visions

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Angrites

June 1, 2012

Angrites

Angrites are achondrites consisting largely of augite.  Augite is a pyroxene containing calcium and, in this case, some titanium and aluminum.  Olivine and plagioclase make up the remaining bulk.  Angrites are the oldest known igneous rocks and probably came from a large parent body. Here are four photos each of three different angrites D’Orbigny   [...]

Column: Micro Visions

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Almahata Sitta

May 1, 2012

Almahata Sitta

It seems understatement to say that Almahata Sitta is polymict given that it contains at least twelve lithologies.  Since the  lithologic types are dominated by ureilites, though, it is classified as a polymict ureilite.  Much of the remainder is EL and EH chondrites of various petrographic grades, melts and breccias.  Also found are H and [...]

Column: Micro Visions

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NWA 6007 L3.5

April 1, 2012

NWA 6007 L3.5

NWA 6007 is terrestrially fresh but shocked. It has well defined chondrules as you would expect of an L3.5. Compression has caused an orientation of components within the stone. Dark inclusions are scattered throughout.                  

Column: Micro Visions

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An Ungrouped Carbonaceous Chondrite

March 1, 2012

An Ungrouped Carbonaceous Chondrite

NWA 5958 C3.0-ung was 286 grams of fragments. We bought a fragment from Greg Hupé and had thin sections made from it. The Met Bull entry and two papers are here: http://www.lpi.usra.edu/meteor/metbull.php?code=50844 http://www.lpi.usra.edu/meetings/lpsc2011/pdf/2343.pdf http://www.lpi.usra.edu/meetings/lpsc2011/pdf/2325.pdf                      

Column: Micro Visions

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Estherville Meteorite, a Mesosiderite

February 1, 2012

Estherville Meteorite, a Mesosiderite

Mesosiderite meteorites are stony irons with roughly 50-50 proportions of each. The iron is asteroidal core and the stone is the crust of a differentiated asteroid. Mantle material is rare. Several formation scenarios have been proposed and scientists continue to discuss the matter. Mesosiderites are classified by mineralogy and texture. Estherville is an A3/4. That [...]

Column: Micro Visions

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Metal-troilite Intergrowths

January 1, 2012

Metal-troilite Intergrowths

Sometimes melt rock in meteorites contains blebs of metal-troilite (FeS) intergrowths. Here are examples from two rocks. NWA 869 is the well known L3-6 regolith breccia. It took a pounding on the surface of its parent body and contains a variety of clasts including melt rock. All 95 grams of NWA 6579 is melt rock. [...]

Column: Micro Visions

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Moorabie L3.8-an

December 1, 2011

Moorabie L3.8-an

A few of us were talking meteorites when one friend mentioned Moorabie. When I couldn’t recall the stone I was admonished to refresh my memory as soon as possible. I make amends with this column. Even before checking my small collection I consulted David Weir’s Moorabie page to see what the score was. He lays [...]

Column: Micro Visions

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Vugs and Vacuoles in D’Orbigny Meteorite

November 1, 2011

Vugs and Vacuoles in D’Orbigny Meteorite

D’Orbigny The D’Orbigny angrite is famous for a lot of things. Among them are holes – vugs and vacuoles. The irregular vugs are usually filled with a tangle of well formed dark augite crystals. The vacuoles or vesicles are spherical. Most are empty. Some contain glass. These three dimensional features are hard to appreciate in [...]

Column: Micro Visions

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