Studies on an Iron Meteorite found near Blacksburg, VA

1
Studies on an Iron Meteorite found near
Blacksburg, VA
Mark A. Stegner and Protip K. Ghosh
Geology Department
Results 1. Strong magnetic response 2.
Atmospheric ablation marks and regmaglypts (Fig.
1) 3. Glassy rind (Fig. 1) 4. Metallic core
(95) composed of iron and nickel (Fig. 2)
5. Minerals identified
Kamacite Fe (93-96) Ni (4-7) iron
rich (Fig. 3 A,B) Taenite Fe
(60-80) Ni (20-40) nickel rich (Fig. 5
A,B,C) Schreibersite Fe (55)
Ni (14) P (31) accessory (Fig. 6 A,B)
Unidentified Silicate Mg, Si, P, S
silicate (Fig. 7) Troilite
Fe S Other small minerals
embedded in Taenite and Schreibersite.
6. Structures seen
Widmanstätten pattern (Very coarse) (Fig. 2)
Neumann Lines
(Fig. 4) 7. Chemical analysis
Ni (mg/g) Co (mg/g) Ga (?g/g) Ge
(?g/g) Cu (?g/g) Cr (?g/g)
67.3 6.3 168 293
123 5.3 Discussion 1. The
sample is a meteorite collected near Blacksburg,
Va. 2. The magnetic strength
separates this sample from slag material that
may have similar appearance.
3. The presence of regmaglypts
(thumb-shaped indentations caused by
melting on atmospheric entry) along with the
smaller ablation pits,
demonstrate that this sample is
extra-terrestrial. 4. The glass rind
on the outside surface also points to fusion
during atmospheric entry. This
rind also prevented weathering. 5. The
freshness of the iron and nickel, seen on the
inside, also points to a
non-terrestrial origin. It is very rare to find
such un-oxidized terrestrial
material. 6. The Widmanstätten
pattern, which is a pattern produced between the
kamacite and taenite interface,
confirms this is a meteorite.
Widmanstätten patterns develop in a zero-G
environment and on very slow
cooling. 7. The presence of Neumann
Lines, which appear as fine parallel lines
running in (up to) six directions,
indicates impact with another body.
These lines are caused by twinning due to
post-consolidation compression.
8. The high Fe-Ni constituents identify
this as an Iron meteorite. 9. The
band-width of the kamacite within the
Widmanstätten pattern (average gt
2 mm), and the content of Ni around 6.7,
indicates that this is a coarse
octahedrite. 10. The Ga-Ni and Ge-Ni
concentrations, when compared to other
reported octahedrite values, points to the
fact that this is a IAB type
iron. (Fig. 8) The Ga content is rather high, but
high Ga values are known in some
octahedrites. 11. Schreibersite, and
minor amounts of silicate minerals, are known to
occur in octahedrites.
Abstract In early 2004 the Marshall University
Geology Department obtained a sample of a
meteorite found by Mr. Skip Spencer of
Charleston, WV. It was found near Blacksburg,
VA. The purpose of this study was to confirm that
the sample was a meteorite and to classify it as
to its type. The sample was highly magnetic, had
a black fusion crust, and showed the presence
at the surface of regmaglypts (thumbprint
shaped atmospheric burn marks). The
meteorite was cut in two with a rock-saw and then
polished to a high sheen with 1? alumina paste.
The polished surfaces were etched using a
solution of ethyl alcohol (90) and nitric acid
(10). The etched samples were then studied with
a polarizing microscope and with a Scanning
Electron Microscope (SEM-EDS). Based on
preliminary chemical, mineralogical, and
structural studies, this meteorite can be
classified as a coarse to medium Octahedrite,
type IAB. Minerals identified are the two Fe-Ni
minerals kamacite (Ni,lt 6) and taenite (Ni, gt
25), schreibersite ((Fe, Ni)3 P), and a silicate
mineral (probably olivine ((Mg, Fe)2 Si O4 ).
Etching clearly showed the Widmanstätten pattern,
formed by the intergrowth of kamacite and taenite
lamellae. Also seen at places are Neumann Lines,
fine sets of parallel lines created within
kamacite due to the development of twinning.
Further analyses of trace elements (Ge, Ga, Ir)
is being conducted to determine the exact
classification and also to determine whether this
sample is related to an octahedrite (Dungannon)
previously reported from Virginia.
Fig. 2 Sample after cutting, polishing, and acid
etching.
Fig. 1 Outside surface before preparation.
Fe Ni
Fig. 3B Kamacite S.E.M. X-ray spectrum analysis
(Iron - Nickel)
Objective This study was conducted to determine
if this sample is a meteorite. Finding that it
is a meteorite an attempt will be made to
identify the minerals present and classify the
meteorite into its chemical and structural
classes.
Fig. 3A Kamacite under S.E.M. Magnified x 100

• Material and Methods
• Meteorite sample collected by Skip Spencer
  (retired geologist)
• Rock saw Lapidary polishing wheel
  
• 120 to 800 grit paper alumina polishing paste
  (1 ?)
• Ethyl alcohol, Nitric acid, Hydrochloric acid
  
• Standard solutions of Ni, Co, Ga, Ge, Cu, and Cr
  
• Scanning Electron Microscope (SEM - EDS)
  
• Inductively Coupled Plasma Spectrometer
  (ICP-AES)
• Petrographic Microscope
• The meteorite was first tested for magnetic
  strength as a general test.
• The surface was then observed for atmospheric
  ablation characteristics
• with a petrographic microscope.
• The meteorite was then cut on a rock saw. This
  presented great difficulty
• due to the strongly crystallized metal and
  the frictional heat of sawing
• causing expansion pinching of the blade.

Fig. 4 Neumann Lines under S.E.M. X 500 Appear
as closely spaced parallel groves.
Fig. 5A Taenite Composition under S.E.M. X-ray
analysis Note that lighter areas mark higher
concentration.
Conclusions 1. This sample is certainly
a meteorite. 2. The Widmanstätten
band-width, and the Ni, Ga, and Ge contents, all
classify this as an IAB
octahedrite. 3. The chemical composition
of this meteorite is markedly different from
the only other iron meteorite
(Dungannon) found in Virginia
Ni (mg/g) Co (mg/g) Ga (?g/g) Ge (?g/g)
Cu (?g/g) Cr (?g/g) This sample 67.3
6.3 168 293
123 5.3 Dungannon 69.5
4.72 78.8 332
153 27 4.
Although the analytical method (ICP) used for
this study is somewhat
semi-quantitative, there is a strong chemical
indication that this meteorite
found near Blacksburg is distinctly different
from the Dungannon meteorite.
5. A strong case can be made that this is a
previously unreported meteorite
find. 6. Further work will involve
chemical analysis by a better quantitative
technique, and a closer control on the
exact location and date of
collection.
Fig. 5B Taenite Analysis Note the significantly
higher nickel.
Fig. 5C Taenite S.E.M. X 350 Note the scale
bars size. The light colored areas are
Schreibersite inclusions.
Fig. 7 Silicate under S.E.M. X 100 Note
texture.
Final Classification Iron Coarse Octahedrite
Type 1AB
References New England Meteoritical Services
www.meteorlab.com Weir, David. Meteorite
Information www.geocities.com/CapeCanaveral/9278
/menu2.htm Darling, David. Classification of Iron
Meteorites www.daviddarling.info/encyclopedia/I/i
ron_meteorite.html McDonough, W.F. Comp. Model
for the Earths Core. Treatise on Geochemistry,
Vol. 2, p.547-568, 2003 Acknowledgements Skip
Spencer (Retired Geologist) Who kindly
supplied the original specimen. Dr. Aley
El-Shazly (MU Geology) For help with
analyses. Dr. Mike Norton (MU Chemistry)
Standars for analysis.
Fig. 6A Schreibersite band S.E.M. X 200
Fig. 6B Schreibersite analysis Note the
presence of phosphorous.