Studies on an Iron Meteorite found near Blacksburg, VA
This presentation is the property of its rightful owner.
Sponsored Links
1 / 1

Studies on an Iron Meteorite found near Blacksburg, VA PowerPoint PPT Presentation


  • 87 Views
  • Uploaded on
  • Presentation posted in: General

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)

Download Presentation

Studies on an Iron Meteorite found near Blacksburg, VA

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Studies on an iron meteorite found near blacksburg va

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 > 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,< 6%) and taenite (Ni, > 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. 1Outside 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.

  • The cut sample was polished using grit paper on a lapidary wheel; the final

  • polishing was done with the alumina paste. The resulting surface had

  • mirror quality reflectance.

  • The polished surface was etched for approximately thirty minutes with a

  • mixture of ethyl alcohol (90%) and nitric acid (10%).

  • Once etched, the sample was prepared for the S.E.M. by immersion in

  • alcohol for dehydration, and then the alcohol volatized at 150o C. The

  • sample was placed directly into the S.E.M. with landmarks referenced

  • with graphite paint. A piece of 100% copper was used as the EDS

  • standard.

  • For chemical analysis, a small slice of the meteorite was dissolved in acid.

  • The ‘stock’ solution thus obtained was analyzed for Ni, Co, Ge, Ga, Cu,

  • and Cr by the ICP-AES. ‘Standard Addition’ method was used to avoid

  • matrix effects.

  • The remaining part of the meteorite has been preserved using a coating of

  • paraffin wax and stored with silica gel.

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 bar’s 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/iron_meteorite.html

McDonough, W.F. Comp. Model for the Earth’s 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.


  • Login