Optical Microscopy of Meteoritic Metal

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Mifflin (L5)

Fell in Wisconsin on April 14, 2010

 

 

Slice of Mifflin showing a brecciated texture (15 gram personal collection specimen). Each box is 1 cm2.

The following micrographs were obtained using a much smaller specimen purchased from Michael Cottingham.  Unfortunately, it is difficult to tell whether this small specimen represents the light or dark portions of the breccia (or both).

 

FIGURE 1: Kamacite (top) and troilite (bottom).  Note how the metal and silicates are intermixed (large amounts of metal-silicate interface).

Magnification: [20-0.80-4.0]

 

FIGURE 2: Kamacite with Neumann lines.  Many of the slip lines exhibit a slight curvature indicative of plastic deformation after shock.  The identity of the lightly-etched/stained mineral to the left is undetermined.

Magnification: [20-0.80-4.0]

 

FIGURE 3: Kamacite with curved Neumann lines.

Magnification: [20-1.00-4.0]

 

FIGURE 4: Zoned taenite showing an outer taenite rim, cloudy zone, and a martensite interior.

Magnification: [100-0.80-4.0]

 

FIGURE 5: Kamacite (with Neumann bands) intergrown with silicate minerals.

Magnification: [20-0.80-4.0]

 

FIGURE 6: Mixture of zoned taenite + troilite + tetrataenite + copper.  This curious but common texture represents a low-temperature modification of the original zoned taenite cloudy structure.   Evidence of localized shock-melting?

Magnification: [100-1.00-4.0]

 

FIGURE 7: Zoned taenite showing an outer taenite rim, cloudy zone, and a martensite interior.

Magnification: [50-0.80-4.0]

 

FIGURE 8: Zoned taenite showing an outer taenite rim, cloudy zone, and a martensite interior.

Magnification: [50-1.00-4.3]

 

FIGURE 9: Zoned taenite showing an outer taenite rim, cloudy zone, and a martensite interior.  Curiously, the taenite substructure is asymmetrical with the outer taenite rim and cloudy zone structures completely missing from the bottom of the metal particle.

Magnification: [50-1.00-4.0]

 

FIGURE 10: Kamacite containing deformed Neumann bands.  The identity of the lightly-etched/stained mineral to the upper right  is undetermined.

Magnification: [20-0.80-4.0]

 

FIGURE 11: Kamacite with troilite inclusion.

Magnification: [20-0.80-4.0]

 

FIGURE 12: Kamacite with Neumann bands.

Magnification: [20-0.80-4.0]

 

FIGURE 13:Mixture of zoned taenite, troilite, tetrataenite, and copper.  This is a curious but common textures that represents a modification of the original zoned taenite cloudy structure at low temperatures.  Evidence of localized shock-melting?

Magnification: [50-0.80-4.0]

 

FIGURE 14: Kamacite with deformed Neumann bands.  The identity of the lightly-etched/stained mineral at the bottom  is undetermined.

Magnification: [20-0.80-4.0]

 

FIGURE 15:Zoned taenite (upper left) and troilite (lower right).  Near the bottom of the zoned taenite, the original cloudy structure has decomposed into a mixture of tetrataenite and kamacite. Note the wide outer taenite rim where the metal touches troilite.

Magnification: [50-0.80-4.0]

 

FIGURE 16: Zoned taenite showing an outer taenite rim, cloudy zone, and a martensite interior.

Magnification: [50-0.80-4.5]

 

FIGURE 17: Taenite grains (polycrystalline). The grain to the left contains numerous troilite blebs and the cloudy structure has decomposed to a mixture of kamacite and tetrataenite.

Magnification: [20-1.00-4.5]

 

FIGURE 18: Close-up of the decomposed taenite region showing tetrataenite + kamacite + troilite intergrowth.

Magnification: [50-1.00-4.5]