[meteorite-list] DIAMOND IN THE CANYON DIABLO IRON

From: Robert Verish <bolidechaser_at_meteoritecentral.com>
Date: Thu Apr 22 10:25:43 2004
Message-ID: <20030522222415.83055.qmail_at_web80510.mail.yahoo.com>

http://www.minsocam.org/msa/collectors_corner/arc/diamondm.htm

American Mineralogist - Volume 24, pages 677-680, 1939


IDENTIFICATION OF DIAMOND IN THE CANYON DIABLO IRON

C. J. KSANDA, Geophysical Laboratory, Carnegie
Institution of Washington, and E. P. HENDERSON,* U. S.
National Museum, Washington, D. C.

   The first good evidence of diamond in a known
meteorite was published in 1888, by Jerofejev and
Lacbinov.(1) In a stony meteorite which fell in
September 1886, near Novo-Urei, they found grayish
grains which were regarded as diamonds. Kunz(2) was
able to procure a small piece of the same meteorite
and substantiated their conclusion.


FIG. 1. Section of Canyon Diablo meteorite showing the
area in the center of the meteoritic iron from which
the diamonds were removed.

     In 1891 Foote(3) reported hard particles in the
Canyon Diablo iron. Much. subsequent work in which the
mode of occurrence and general crystallographic
appearance of these grains are described, is reviewed
by Farrington.(4)

     Recently small black grains embedded in a slice
from a Canyon Diablo iron have been identified by
means of the x-ray powder spectrum method and by
microscopic examination as diamonds. The specimen
containing these diamonds was purchased by the U. S.
National Museum from H. H. Nininger, Denver, Colorado,
who while cutting the specimen found small dark
inclusions that resisted the saw, and assumed that
they were diamonds. The section of iron shown in Fig.
1 is 115 mm. long, 55 mm. wide at its widest part, and
weighs 411.7 grams. The specimen was not further
polished in the U. S. National Museum laboratories
because to do so would probably grind away several of
the small diamonds visible to the naked eye.



FIG. 2. The cavity enlarged 6X, containing black
diamonds, showing larger individuals lining the inner
wall, securely embedded in graphite. Arrow points
indicate the location of larger grains of black
diamonds partly excavated.

     The diamonds occur associated with some graphitic
material within a troilite area. Immediately
surrounding the troilite is a series of irregular
areas of schreibersite. A wax dam was constructed
around the area and the diamonds were freed by
repeated treatments of nitric and hydrochloric acid.
The insoluble residue was washed out and saved. This
residue was slightly contaminated with some organic
matter as the acid reacted with the wax dam. The black
grains were repeatedly boiled with mixed acids and the
acid soluble portion decanted off and rejected.

     About 50 individual black grains were recovered
whose sizes vary from 0.1 to 0.6 mm. The cavity made
by the acid (see Fig. 2) is lined with larger
individuals securely embedded in the graphite and
troilite. Several of these black grains were removed
by working them out with a needle point. The largest
was 0.9 mm. in diameter.

     The grains resemble the black diamond, or
carbonado, of commerce. Under the microscope they are
black, and as recovered are porous, and therefore seem
to consist of minute individuals. A rude layering
appears in the larger grains. They are more easily
broken down than ordinary black diamond.(5)

     Grains rubbed between two pieces of ordinary
black diamond did not produce any scratches visible
with the microscope.

     X-ray analysis. Crushed particles were mounted on
a fine thread by means of a film of vacuum grease and
a photograph was taken with Cu-K radiation in a
circular camera of an effective radius of 57.2 mm. The
specimen was rotated uniformly during the exposure.
The results of the x-ray analysis are given in Table
1. The diffraction pattern shows only the lines
theoretically possible within the angle of reflection
with Cu radiation for the cubic lattice of diamond.
The systematically absent reflections are
characteristic of the face-centered lattice type of
diamond. The unit cell dimension, do=3.557, calculated
from spacings d/n is in agreement with previously
published data.(6)

X-ray powder photographs of the graphitic mass were
also taken. The resulting diffraction pattern shows a
large number of lines,7 not all of which could be
identified. Of the 16 lines measured on the film, only
nine are identical in position and intensity with the
first nine lines of the known graphite structure.(8)
No lines characteristic of diamond were found on these
films.

     Optical properties. Under the microscope, in a
melt of sulfur and selenium, most crushed grains were
not transparent except in irregular patches at thin
edges, where they were isotropic; n for orange colored
light is greater than 2.37 and for yellow light about
2.42.(9)

* Published by permission of the Secretary of the
Smithsonian Institution.

1) Jerofejev, M., and Lachinov, P., Zapiski
Mineralogicheskoe Obshchestvo, Leningrad, (2) 24,
263-294 (1888).

2) Kunz, G. F., Science, 11, 118-119 (1888).

3) Foote, A. E., A new locality for meteoric iron with
a preliminary notice of the discovery of diamonds in
the iron: Am. J. Sci. (3), 42, 413-417 (1891).

4) Farrington, O. C., Meteorites; their Structure,
Composition and Terrestrial Relations. By author.
Chicago, 1915.

5) Black diamonds (or carbonado) such as those used
for industrial purposes consist usually of a very
compact mixture of gray to black and translucent white
particles in various proportions, intimately
intergrown. The individual crystals are of microscopic
size, and the structure when fractured is
fine-grained.

6) Wyckoff, R. W. G., The Structure of Crystals, 2nd
Ed., Chemical Catalog Co., Inc., New York, 1931.

7) The specimen appeared slightly altered by previous
treatment and etching of the cavity with acid.

8) See, for example, Hofmann, U., and Wilm, D., Zeits.
f. Elektrochem., 42, 504-522 (1936).

9) The optical properties were determined by Dr. H. E.
Merwin, and his aid in this investigation is
gratefully acknowledged.



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Received on Thu 22 May 2003 06:24:15 PM PDT