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American Mineralogist, Volume 88, pages 1817–1821, 2003
0003-004X/03/1112–1817$05.00 1817
INTRODUCTION
The terrestrial origin of silicon carbide (SiC = moissanite)
samples has been the subject of controversial debates during
the last century. Since the discovery of SiC crystals as inclu-
sions in natural diamonds in kimberlites (Moore et al. 1986;
Moore and Gurney 1989; Otter and Gurney 1989; Leung 1990)
and in lamproites (Jaques et al. 1989), however, the natural
occurrence of moissanite in terrestrial rocks has been widely
accepted.
The first discovery of naturally formed SiC dates back to
1904, when Moissan reported its occurrence from the Canyon
Diablo Fe meteorite. However, Moissan’s finding was thought
to be an artifact (Mason 1967) from SiC-bearing cutting tools
used to prepare the meteorite samples. Since then, reports of
new occurrences of natural SiC (e.g., Regis and Sand 1958;
Bobrievich et al. 1957; Bauer et al. 1963; Marshintsev et al.
1967; Kaminskiy et al. 1969; Moskvitin et al. 1978; He 1984;
Jaques et al. 1986; Marshintsev 1990; Filippidis 1993) have
been debated vigorously and many geologists considered a
natural terrestrial origin as highly improbable (e.g., Milton and
Vitaliano 1984; Woermann and Rosenhauer 1985, p. 316). The
* Present address: UMR CNRS 5570, Laboratoire de Sciences
de la Terre, ENS Lyon, France. E-mail: simonpietro.di.pierro@
ens-lyon.fr
LETTERS
Rock-forming moissanite (natural
aa
aa
a-silicon carbide)
SIMONPIETRO DI PIERRO,
1,
* EDWIN GNOS,
2
BERNARD H. GROBETY,
1
THOMAS ARMBRUSTER,
3
STEFANO M. BERNASCONI,
4
AND PETER ULMER
4
1
Department of Geosciences, Mineralogy and Petrography, University of Fribourg, Switzerland
2
Institute for Geology, Baltzerstrasse 1-3, University of Bern, Switzerland
3
Laboratory of Chemical and Mineralogical Crystallography, University of Bern, Switzerland.
4
Department of Earth Sciences, ETH Zürich, Switzerland
ABSTRACT
We report the first occurrence of moissanite (SiC) as a rock-forming mineral (8.4 vol%) in one
unique specimen of a terrestrial rock. The sample has a homogeneous, porphyritic texture, and was
found as a beach pebble thought to be derived from a Tertiary volcanic province of the Aegean Sea
region. The matrix is bluish-colored and consists of very fine-grained brucite, calcite, and magnes-
ite, in which macrocrysts of quartz (25.3 vol%) and moissanite are found. Other accessory phases
are phlogopite-3T, magnesiochromite, an Fe-rich phase, Cl-bearing brucite, Al-rich orthopyroxene,
and unidentified MgFe-silicates (4 vol%). The bulk-rock composition shows a “kimberlitic” chem-
istry (55.8 wt% SiO
2
, 28.5 wt% MgO, 1.4 wt% CaO, 18.1 wt% LOI). Colorless gemmy, and blue or
black moissanite crystals are subhedral and display characteristic hexagonal symmetry (6H polytype).
Most moissanite grains contain metallic Si and Fe-silicide (Fe
3
Si
7
) inclusions, and more rarely, other
Fe-silicides with varying amounts of Al (£24.5 wt%), Ca (£8.0 wt%), Mn (£6.8 wt%), Ti (£16.3
wt%), and Ni (£2.6 wt%). The d
13
C value of the moissanite is –28.1‰. According to available data,
the f
O
2
stability field of SiC is five to six log units below the iron-wüstite (IW) buffer curve. There-
fore, the observed Fe-bearing silicates cannot have been equilibrated with SiC under ambient pres-
sure. Instead, our finding indicates that the rock most likely formed at the ultrahigh-pressure conditions
of the upper mantle or transition zone.
issue of a possible contamination with synthetic SiC from abra-
sives could have been, instead, ruled out in more recent reports
of SiC found in meteorites, as measured isotopic anomalies in
many trapped elements could definitely be identified as presolar
in origin (e.g., Bernatowicz et al. 1987; Tang et al. 1989; Lewis
et al. 1990; Daulton et al. 2002).
Typically, moissanite has been found as a constituent of
kimberlitic pipes or in associated volcanic rocks. Recently, well-
ordered a-SiC and b-SiC crystals were found as inclusions
within diamonds (Leung 1990) and dispersed in the matrix of
kimberlites from Fuxian, China (Leung et al. 1990). Leung et
al. (1996) discussed the heteroepitaxial intergrowth between
b-SiC and diamond along the (110) plane as a possible mecha-
nism for the genesis of natural diamonds. Mathez et al. (1995)
investigated the chemical composition of metallic Si and Fe-
silicide inclusions in moissanite grains extracted from
kimberlites from Yakutia, Russia. They also presented C-iso-
tope data of moissanite grains, which were clearly distinguish-
able from interstellar SiC (e.g., Stone et al. 1991; Zinner et al.
1989). According to Mathez et al. (1995, p. 781–782), chemi-
cal and mineralogical data obtained from the SiC, the inclu-
sions, and the associated minerals “…leaves little doubt that
SiC occurs naturally and is present in the Earth’s mantle…”
and “…establish that SiC…is a widespread, albeit rare, phase
in diamond-bearing rocks.”
Moissanite, besides diamond, is a potential “window” into
DI PIERRO ET AL.: ROCK-FORMING MOISSANITE1818
the redox conditions of the Earth’s mantle. The current study
characterizes one unique specimen of a newly discovered rock
pebble containing 8.4 vol% SiC, thought to be associated with
calc-alkaline volcanic rocks. Moissanite is, to our knowledge,
reported for the first time in rock-forming quantities. In con-
trast to previous studies, where moissanite grains were obtained
from heavy mineral concentrates or as inclusions in diamonds,
the present occurrence allows the study of textural relation-
ships between SiC and the other phases using conventional
polished thin sections.
SAMPLE AND METHODS
One unique specimen was found at a beach along the Turkish coast of the
Mediterranean Sea, around 150 km NW from Izmir, and is most likely derived
from Tertiary volcanic rocks outcropping in the area. The source outcrop, how-
ever, has not yet been located. The sample displays an unusual bluish color (Fig.
1a). It is macroscopically homogeneous and texturally isotropic. It was collected by
Mr. Salvatore Musacchia and given to the first author as a “curiosity.”
The sample has been analyzed by optical microscopy, powder X-ray dif-
fraction (XRD, Philips PW 1800, CuKa radiation, 2–65 ∞2q), X-ray fluores-
cence (XRF, Philips PW 2400 spectrometer), scanning electron microscopy with
energy dispersive system (FEI SEM-EDS XL30 Sirion, operating conditions 20
kV), and a Multiphase Carbon Determinator (Leco RC 412). Single-crystal data
were obtained on an ENRAF NONIUS CAD4 X-ray diffractometer, using a
graphite monochromator and MoKa X-radiation at room temperature (293 K).
Electron-microprobe analyses of silicates and oxides were obtained with a wave-
length-dispersive system (Cameca SX-50: operated at 15 kV accelerating po-
tential with a 20 nA beam current, counting times were 20 s on peak and
background for major elements and up to 40 s for trace elements); a synthetic
SiC standard was used for moissanite, and Si and Fe metal standards were used
for metallic inclusions (10 nA beam current). Physical conditions of
cathodoluminescence analyses were 25 kV and 90 mA. The C-isotope ratio of
the SiC was determined by flash combustion using a Carlo Erba CNS elemental
analyzer coupled in continuous flow to a Micromass Optima mass spectrom-
eter. Carbon- and O-isotope ratios of the carbonate were determined by reaction
at 90 ∞C with 100% phosphoric acid on an automated carbonate device con-
nected to a VG-PRISM mass spectrometer. Mineral modes were determined by
point counting (2400 points). Moissanite crystals were separated from the sample
by etching away the matrix in a 5% HCl solution. XRD powder, XRF, SEM and
Leco analyses were performed at the University of Fribourg. XRD powder, XRF,
SEM and Leco analyses were performed at the University of Fribourg. XRD
powder, XRF, SEM, and Leco analyses were performed at the University of
Fribourg. XRD single crystal, EMPA, and CL analyses were performed at the
University of Bern. Isotopic analyses were performed at the ETH-Zürich.
RESULTS
The bulk-chemical composition obtained by XRF (Table 1)
shows that SiO
2
, MgO, and CaO are the only oxides present in
significant quantities, all the other analyzed major and trace
elements show very low concentrations. The volatiles (H
2
O and
CO
2
) are also present in significant quantities. The principal
phases are moissanite (8.4 vol%) and undeformed,
xenomorphic, mm-sized and inclusion-free quartz grains (25.3
vol%), dispersed in a brucite-dominated matrix (58.2 vol%)
also containing calcite, magnesite, phlogopite-3T, Cl-bearing
brucite, magnesiochromite, Al-rich orthopyroxene, two uniden-
tified MgFe-silicates, and an unidentified Fe-rich phase. Quartz
and moissanite are never observed in direct contact with each
other. The MgFe-silicates are reddish and yellowish in color,
and have compositions intermediate between olivine and
orthopyroxene. Spherical structures or “globules,” ranging in
diameter from a few hundred micrometers to a millimeter, are
dispersed throughout the groundmass. These globules have the
same mineral assemblage as the bulk but a smaller grain size,
FIGURE 1. (a) Photo of the SiC-rich specimen. Black spots are
moissanite crystals. Scale bar is 2 cm. (b) Gemmy, platy crystal of
moissanite shown with largest (001) face. The arrow indicates a drop-
shaped, black metallic inclusion. Scale bar is 300 mm. (c) Back-
scattered electron image of metallic inclusion in moissanite. The gray
shading in the BSE image consists mainly of pure metal Si (Table 2).
The brighter areas in the middle and along the rims of the inclusion
are composed of Fe-silicide. The very bright irregular white spots are
likely inclusions of a third phase with higher average atomic number.
Scale bar is 200 mm.
and account for 6.2 vol% of the bulk sample. Crystals of light-
blue Cl-bearing brucite (1.9 vol%), a few micrometers in size,
are homogeneously scattered throughout the matrix and are re-
sponsible for the bluish color of the pebble. All unidentified
DI PIERRO ET AL.: ROCK-FORMING MOISSANITE 1819
phases are microcrystalline and
subject of on-going studies.
Separated moissanite
crystals range between 0.2
and 1.5 mm in size, are blue
or black in color, and have a
metallic luster. Some com-
pletely transparent gemmy
crystals with brilliant sub-
adamantine luster are present
as well (Fig. 1b). In general,
the crystals show well-devel-
oped crystallographic faces,
but some are corroded or frac-
tured. They have a character-
istic platy or elongated,
pinacoidal, hexagonal shape
bounded by {100} faces (a-
SiC). The unit-cell dimensions obtained with the single-crys-
tal X-ray diffraction analysis on three grains are a = 3.080(1)
Å and c = 15.12(1) Å (6H polytype). In a standard thin section
(5 ¥ 2 cm), at least 341 crystals of moissanite have been counted.
Under transmitted light, moissanite ranges from colorless to
light blue, or dark blue to almost black. Greenish-yellow or
pinkish crystals also have been observed. Some moissanite
grains are pleochroic, others are probably twinned. The optical
character is always uniaxial positive. Moissanite grains are
commonly associated closely with the red MgFe-silicates,
which are commonly in contact with SiC crystal faces. A simi-
lar mineral paragenesis has been described by Mathez et al.
(1995) for natural SiC crystals from Yakutia. The moissanite
crystals are very homogeneous chemically, with none of the
analyzed elements other than Si present above the detection
limit (Table 2). A few moissanite grains show yellow, blue,
and red cathodoluminescence. Yellow luminescence is confined
to grain boundaries. Carbon-isotope data were obtained on
moissanite and on carbonates. The moissanite has a d
13
C value
of –28.1‰ relative to the Pee Dee belemnite standard (PDB),
and the bulk carbonate yielded a d
13
C value of –11.9‰ and a
d
18
O of –3.6‰. Carbon isotope analyses have been performed
also on a synthetic SiC sample and a value of –27.1‰ was
obtained. The C-isotope signature, therefore, is not well suited
to distinguish natural terrestrial SiC from synthetic SiC.
One third of the examined moissanite crystals contain me-
tallic inclusions with rounded shapes. The average size of the
inclusions is between 50 and 100 mm, with a maximum of 400
mm. Most of the inclusions occur inside the crystals. A few
metallic grains have been found along moissanite crystal bound-
aries or dispersed in the brucitic matrix. Crystals with more
than one inclusion are rare (max 10 inclusions). Pure Si is the
most common inclusion. Fe-silicides are present along the Si
metal-SiC boundaries (Fig. 1c), or form exsolution domains in
metallic Si. Fe
3
Si
7
is the most common Fe-silicide. This phase
is stable at ambient pressure above 937 ∞C and decomposes to
Si and FeSi
2
at lower temperatures (Kubaschewski 1982). Man-
ganese and Ni substitute for Fe in various proportions in Fe
3
Si
7
(Table 2). Other silicide-containing phases have variable stoichi-
ometries and were classified as Si-Fe-Al-Ca and Si-Fe-Ti (possi-
bly alloys), and as Si
2
(Fe,Al,Ca)
3
and Si
3
(Fe,Al)
2
(probably sto-
ichiometric compounds) phases. Another metallic phase consists
of Si
2
Ca (tentatively stoichiometric compound) (Table 2).
ARTIFICIAL VS. NATURAL
An artificial origin of the beach pebble may be suspected
considering the large quantity of SiC crystals and the presence
of quartz in an ultramafic matrix. Moreover, the outcrop from
which the specimen may have originated has not been located
yet. There are, however, a number of indications that the mate-
rial is natural. The beach where the pebble was collected is in
an unpopulated region, around 40 km away from the closest
village and 150 km away from the closest industrial town. A
thorough investigation of the patent literature concerning SiC,
as well as inquiries with different synthetic SiC producers (e.g.,
Timcal AG. Ticino, Switzerland) using the Acheson method
(e.g., Knippenberg 1963) and their industrial customers (e.g.,
Smyris s.r.l. Milano, Italy), gave no indications that the pebble
as a whole or the silicon carbide per se could have been a syn-
thetic product.
In contrast, all analytical results are typical for natural
moissanite.
(1) In synthetic SiC processed either with or without addi-
tives, C constitutes the major impurity phase and has a gra-
phitic character (Backhaus-Ricoult et al. 1993, p. 2204). Other
reported inclusions, all always nanometer-sized, are B
4
C and
B
25
C, metallic Fe and Si, and FeSi and Ti
5
Si
3
precipitates (e.g.,
More et al. 1986; Backhaus-Ricoult et al. 1993; Munro 1997).
In the present sample, neither graphite nor any other form of
C-bearing inclusions have been found.
(2) The metallic inclusions are characteristic, although not
unequivocal (e.g., Lyakhovich 1980, p. 965), indicators of the
natural origin of the moissanite crystals. Many silicide and al-
loy compositions have been observed previously in natural SiC:
metallic Fe by Bauer et al. (1963); native Si and Fe by Leung
(1990) and Leung et al. (1990); native Si and ferrosilicide by
Marshintsev (1990); micrometer-sized metallic Si, ferrosilicide
(Fe
3
Si
7
), and light rare earth element (LREE) rich Fe-Ti-Zr si-
licides (up to 16 wt% Ce and up to 4 wt% Th) by Mathez et al.
(1995). Except for the LREE-rich metallic phases, all the above
TABLE 1. Bulk rock chemistry
XRF 1s d.l. XRF 1s d.l. Leco
SiO
2
55.84 0.25 0.01 Ba b.d. 20 12 CO
2
* 1.96
TiO
2
0.02 0.01 0.01 Cr 31 5 5 H
2
O
+
16.19
Al
2
O
3
0.41 0.08 0.01 Cu b.d. 4 4 H
2
O
–
3.61
FeO 0.09 0.05 0.01 Nb 4 2 2
MnO 0.01 0.01 Ni 35 3 3
MgO 28.49 0.02 0.01 Pb b.d. 4 7
CaO 1.43 0.05 0.01 Rb b.d. 3 3
Na
2
O 0.02 0.02 0.01 Sr 46 4 3
K
2
O 0.03 0.02 0.01 V b.d. 6 5
P
2
O
5
0.01 0.01 0.01 Y 51 3 3
LOI 18.13 Zn b.d. 4 3
Zr 13
Total 104.48
Note:
The SiO
2
value includes metallic Si and SiC, which brings the total above 100 wt%. *At
T
max
= 1000 ∞C of
the Leco instrument SiC does not break down. The listed CO
2
content is therefore considered as CO
2
from the
carbonates only. Based on the modal mineralogy, the total CO
2
should be 8–9 wt% (SiC + carbonates), and
approximately 1 wt% Cl should be present too. 1s = relative error; d.l. = detection limit; b.d. = below detection.
Major and minor elements in wt%; trace elements in ppm; CO
2
and H
2
O also in wt%.
DI PIERRO ET AL.: ROCK-FORMING MOISSANITE1820
TABLE 4. EDS semiquantitative analyses
opx 1 opx 2 mg-cr
wt% wt% wt%
SiO
2
47.42 48.87
Al
2
O
3
10.54 7.13 26.35
Cr
2
O
3
1.31 42.57
FeO 13.38 18.96 19.66
NiO 1.86 1.56
MgO 25.49 23.48 11.43
Total 100.00 100.00 100.01
Si 1.717 1.805
Al 0.450 0.310 0.951
Cr 0.038 1.031
Fe 0.405 0.586 0.504
Ni 0.054 0.046
Mg 1.376 1.293 0.522
S cations 4.039 4.040 3.008
Note:
opx = orthopyroxene; mg-cr = magnesiochromite
TABLE 3. Carbon isotopic data for SiC and associated minerals.
Mineral d
13
C Description Source
Moissanite –28.1‰ Bluish pebble this study
Carbonate –11.9‰ Bluish pebble this study
Moissanite –24‰ Fuxian kimberlite Leung et al. 1990
Diamond –2.9‰ to –4.8‰ Fuxian kimberlite Leung et al. 1990
Moissanite –22‰ to –29‰ Yakutia kimberlite Mathez et al. 1995
Diamond –31‰ Yakutia kimberlite Mathez et al. 1995
SiC 6 to 160‰ Interstellar SiC Zinner et al. 1989
SiC 150 to 5200‰ Interstellar SiC Stone et al. 1991
SiC –27.1‰ Synthetic this study
Note:
Uncertainty of the measurements for this study: 0.1‰.
compounds, always at the micrometer scale, have been found
in our sample (Table 2).
(3) Two unidentified MgFe-silicates, with FeO contents
ranging between 3 and 8 wt%, are found throughout the matrix
and in contact with SiC. According to Mathez et al. (1995), Fe-
bearing silicate phases cannot be in equilibrium with SiC un-
der conditions characteristic of the industrial process. At
ambient pressure, the f
O
2
stability field of moissanite is five to
six log units below the IW buffer. Under such conditions, the
Fe in Fe-bearing silicates is reduced to the metallic form and
expelled from the structure. Therefore, in the system Fe-Mg-
Si-O-C, the coexistence of SiC and Fe-bearing silicates is prob-
ably only possible at the ultra-high pressures conditions of the
upper mantle or greater depths.
(4) The moissanite d
13
C value of –28.1‰ is in agreement
with ranges published by Marshintsev (1990), e.g., lower than
–25‰, and Mathez et al. (1995), e.g., –22 to –29‰ for Rus-
sian moissanite, as well as those of Leung et al. (1990), e.g.,
–24‰, for Chinese natural SiC. In natural diamond genesis, a
strongly depleted
13
C isotope signature has been interpreted as
a primary mantle feature (e.g., Deines et al. 1993). Compared
to diamonds, the values for SiC exhibit a much narrower range
(Table 3). The d
13
C values of meteoritic interstellar SiC grains
range from 150 to 5200‰, and thus are far from terrestrial val-
ues (Stone et al. 1991, see Table 3).
(5) The presence of phlogopite (e.g., Dawson and Smith
1975) and brucite (e.g., Berg 1989), the high volatile content
and the presence of globules (e.g., Pell 1997), all point to a
“kimberlitic environment.” The high Mg content of chromite
(>11 wt% MgO, Table 4) is typical for primary mantle-derived
spinel (e.g., Shulze 2001). The high Al content of the
TABLE 2. Electron microprobe analyses of moissanite and metallic inclusions
moissanite silicon iron silicide
wt% SiC SiC 1s d.l. Si Fe
3
Si
7
Si-Fe-Al-Ca Si
2
(Fe,Al,Ca)
3
Si
2
(Fe,Al,Ca)
3
Si
3
(Fe,Al)
2
Si-Fe-Ti Si
2
Ca 1s d.l.
Si 69.67 70.23 0.11 0.03 100.82 52.72 37.48 32.39 33.84 47.13 41.16 56.38 0.39 0.20
Ti b.d. b.d. – 0.03 b.d. 0.55 0.04 0.03 b.d. 0.15 16.27 b.d. 0.02 0.03
Cr b.d. b.d. – 0.05 b.d. 0.08 b.d. b.d. 0.06 b.d. 0.08 b.d. 0.01 0.06
Al b.d. b.d. – 0.01 0.02 0.12 20.99 24.55 22.64 5.51 2.35 0.42 0.01 0.01
Fe b.d. b.d. – 0.06 b.d. 37.14 31.51 33.74 34.13 45.93 37.72 0.07 0.16 0.06
Mn b.d. b.d. – 0.07 b.d. 6.76 0.50 0.50 0.65 1.28 1.65 b.d. 0.02 0.06
Mg b.d. b.d. – 0.03 b.d. b.d. 0.06 0.12 b.d. b.d. 0.01 b.d. 0.003 0.01
Ni b.d. b.d. – 0.08 b.d. 2.61 2.05 1.73 1.63 0.79 1.32 b.d. 0.02 0.10
Ca b.d. b.d. – 0.02 b.d. b.d. 8.01 6.42 6.85 b.d. 0.08 40.52 0.01 0.03
Na b.d. b.d. – 0.02
K b.d. b.d. – 0.02
C 29.80* 30.04*
Total 99.49 100.32 100.90 99.98 100.63 99.49 99.82 100.85 100.65 97.53
Si 1.000 1.000 1.000 6.884 2.284 2.009 2.102 3.058 2.792 1.984
Ti 0.000 0.000 0.000 0.042 0.001 0.001 0.000 0.006 0.647 0.000
Cr 0.000 0.000 0.000 0.005 0.000 0.000 0.000 0.002 0.003 0.000
Al 0.000 0.000 0.000 0.016 1.330 1.584 1.463 0.372 0.166 0.016
Fe 0.000 0.000 0.000 2.439 0.966 1.052 1.066 1.498 1.287 0.001
Mn 0.000 0.000 0.000 0.451 0.015 0.016 0.021 0.042 0.057 0.000
Mg 0.000 0.000 0.000 0.000 0.004 0.008 0.000 0.000 0.000 0.000
Ni 0.000 0.000 0.000 0.163 0.059 0.051 0.048 0.024 0.043 0.000
Ca 0.000 0.000 0.000 0.000 0.342 0.279 0.298 0.000 0.004 0.999
Na 0.000 0.000
K 0.000 0.000
C 1.000 1.000
S cations 2.000 2.000 1.000 10.000 5.000 5.000 5.000 5.000 5.000 3.000
Note:
1s = relative error; d.l. = detection limit; b.d. = below detection.
* Calculated by stoichiometry.
DI PIERRO ET AL.: ROCK-FORMING MOISSANITE 1821
orthopyroxene (>10 wt% Al
2
O
3
, Table 4) points to high equili-
bration temperature (probably >1200 ∞C) (e.g., Danckwerth and
Newton 1974).
The intimate association of SiC and Fe-bearing silicates,
along with the other above considerations, suggest an origin
from the mantle of the present sample. The fact that such an
assemblage is not reported experimentally shows the need for
more detailed ultra-high pressure studies in moissanite-bear-
ing systems.
ACKNOWLEDGMENTS
Salvatore Musacchia, the person who found the bluish pebble, is greatly
acknowledged for providing the material for research. Roberto Compagnoni,
Jürgen von Raumer, Vincent Serneels, and Gretchen Frueh-Green are thanked
for the fruitful discussions. We thank Cristophe Neururer, Cédric Metraux, Jes-
sica Chiaverini, Giulio Galetti, Odette Marbacher, and Paulo Bourqui for lab
assistance and thin sections preparation. Electron-microprobe analyses at the
University of Bern were supported by Schweizerischer Nationalfonds (credit
21-26579.89). We also thank Ed Mathez, Tyrone Daulton, and Robert F. Dymek
for their constructive reviews. Financial support from the Swiss National Sci-
ence Foundation Commission of the University of Fribourg (fellowship n.
PBFR2-101389 to SDP) is greatly acknowledged.
REFERENCES CITED
Backhaus-Ricoult, M., Mozdzierz, N., and Eveno, P. (1993) Impurities in silicon
carbide ceramics and their role during high temperature creep. Journal de Phy-
sique III France, 3, 2189–2210.
Bauer, J., Fiala, J., and Hrichová, R. (1963) Natural a-silicon carbide. American
Mineralogist, 48, 620–634.
Berg, G.W. (1989) The significance of brucite in South African kimberlites. In
Kimberlite and Related Rocks, Volume 2: Their Mantle/Crust Setting, Diamonds
and Diamond Exploration; Geological Society of Australia Special Publica-
tion, 14; 282–296. Blackwell Scientific, Cambridge, England.
Bernatowicz, T., Fraundorf, G., Tang, M., Anders, E., Wopenka, B., Zinner, E., and
Fraundorf, P. (1987) Evidence for interstellar SiC in the Murray carbonaceous
meteorite. Nature, 330, 728–730.
Bobrievich, A.P., Kalyuzhuyi, V.A., and Smirnov, G.I. (1957) Moissanite in
kimberlites of the East Siberian Platform. Doklady Akademii Nauk SSSR,
115(6), 1189–1192 (in Russian).
Danckwerth, P.A. and Newton, R.C. (1978) Experimental determination of the spinel
peridotite to garnet peridotite reaction in the system MgO-Al
2
O
3
-SiO
2
in the
range 900–1100∞ C and Al
2
O
3
isopleths of enstatite in the spinel field. Contri-
butions to Mineralogy and Petrology, 66, 189–201.
Daulton, T.L., Bernatowicz, T.J., Lewis R.S., Messenger S., Stadermann F.J., and
Amari S. (2002) Polytype distribution in circumstellar silicon carbide. Science,
296, 1852–1855.
Dawson, J.B. and Smith, J.V. (1975) Chemistry and origin of phlogopite megacrysts
in kimberlite. Nature, 253, 336–338.
Deines, P., Harris, J.W., and Gurney, J.J. (1993) Depth-related carbon isotope and
nitrogen concentration variability in the mantle below the Orapa kimberlite,
Botswana, Africa. Geochimica et Cosmochimica Acta, 57, 2781–2796.
Filippidis, A. (1993) New find of moissanite in the Metaxades zeolite-bearing
volcanoclastics rocks, Thrace county, Greece. Neues Jahrbuch in Mineralogie
Monatshefte, 11, 521–527.
He, G. (1984) Kimberlites in China and their major components: A discussion on
the physico-chemical properties of the upper mantle. In J. Kornprobst, Ed.,
Kimberlites, I. Kimberlites and related rocks, p. 181–194. Elsevier, Amsterdam.
Jaques, A.L., Lewis, J.D., and Smith, C.B. (1986) The kimberlites and lamproites of
Western Australia. Bulletin of Geological Survey Western Australia, 132.
Jaques, A.L., Hall, A.E., Sheraton, J.W., Smith, J.B., Sun, S.S., Drew, R.M., Foudoulis,
C., and Ellingsen, K. (1989) Composition of crystalline inclusions and C-iso-
tope composition of Argyle and Ellendale diamonds. In Kimberlite and Related
Rocks, Volume 2: Their Mantle/Crust Setting, Diamonds and Diamond Explo-
ration; Geological Society of Australia Special Publication, 14; 966–989.
Blackwell Scientific, Cambridge, U.K.
Kaminskiy, F.V., Bukin, V.I., Potapov, S.V., Arkus, N.G., and Ivanova, V.G. (1969)
Discoveries of silicon carbide under natural conditions and their genetic impor-
tance. International Geology Review, 11, 561–569.
Knippenberg, W. F. (1963) Growth Phenomena in Silicon Carbide. Philips Research
Report, 18, 161–274.
Kubaschewski, O. (1982) Iron-Binary Phase Diagrams, p. 185. Springer-Verlag,
New York.
Leung, I.S. (1990) Silicon carbide cluster entrapped in a diamond from Fuxian,
China. American Mineralogist, 75, 1110–1119.
Leung, I.S., Guo, W., Freidman, I., and Gleanson, J. (1990) Natural occurrence of
silicon carbide in a diamondiferous kimberlite from Fuxian. Nature, 346, 352–
354.
Leung, I.S., Taylor, L.A., Tsao, C.S., and Han, Z. (1996) SiC in diamond and
kimberlites: Implications for nucleation and growth of diamond. International
Geology Review, 38, 595–606.
Lewis, R.S., Amari, S., and Anders, E. (1990) Meteoritic silicon carbide: pristine
material from carbon stars. Nature, 348, 293–298.
Lyakhovich, V.V. (1980) Origin of accessory moissanite. International Geology
Review, 22, 961–970.
Marshintsev, V.K., Shchelchkova S.G., Zol’nikov G.V., and Voskresenskaya V.B.
(1967) New information on moissanite from the Yakutian kimberlites. Geologiya
i Geofizika Novosibirsk, 12, 22–31 (in Russian).
Marshintsev, V.K. (1990) Nature of silicon carbide in kimberlite rocks of Yakutia.
Mineralogicheskiy Zhurnal., 12(3), 17–26 (in Russian).
Mason, B. (1967) Extraterrestrial mineralogy. American Mineralogist, 52, 307–325.
Mathez, E.A., Fogel, R.A., Hutcheon, I.D., and Marshintsev, V.K. (1995) Carbon
isotopic composition and origin of SiC from kimberlites of Yakutia, Russia.
Geochimica et Cosmochimica Acta, 59, 781–791.
Milton, C. and Vitaliano, D.B. (1984) The non-existence of moissanite, SiC. Inter-
national Geological Congress, Abstract, 27 (5), 107–108.
Moore, R.O. and Gurney, J.J. (1989) Mineral inclusions in diamond from the Mon-
astery kimberlite, South Africa. In Kimberlite and Related Rocks, Volume 2:
Their Mantle/Crust Setting, Diamonds and Diamond Exploration; Geological
Society of Australia, Special Publication, 14, 1029–1041. Blackwell Scientific,
Cambridge, U.K.
Moore, R.O., Otter, M.L., Rickard, R.S., Harris, J.W., and Gurney, J.J. (1986) The
occurrence of moissanite and ferro-periclase as inclusions in diamond. In 4
th
International Kimberlite Conference, Perth, Extended Abstracts; Abstract Geo-
logical Society of Australia, 16, 409–411.
More, K.L., Carter, C.H., Bentley, J., Wadlin, W.H., Lavanier, L., and Davis, R.F.
(1986) Occurrence and distribution of Boron-containing phases in sintered a-
silicon carbide. Journal of the American Ceramic Society, 69, 695–698.
Moskvitin, I.Y., Marshintsev, V.K., Mikhaylov, V.A., and Brovkin, A.A. (1978)
Moissanite in Vendian sedimentary rocks of the Botuobuya Saddle, Siberian
Platform. Transaction (Doklady) of the USSR Academy of Sciences: Earth Sci-
ence Sections, 239; 1–6, 138–140.
Munro, R.G. (1997) Material properties of a sintered a-SiC. Journal of Physical and
Chemical Reference Data, 26, 1195–1203.
Otter, M.L. and Gurney, J.J. (1989) Mineral inclusions in diamonds from the Sloan
diatreme, Colorado-Wyoming State Line kimberlite district, North America. In
Kimberlite and Related Rocks, Volume 2: Their Mantle/Crust Setting, Diamonds
and Diamond Exploration; Geological Society of Australia, Special Publica-
tion, 14, 1042–1053. Blackwell Scientific, Cambridge, England.
Pell, J.A. (1997) Kimberlites in the Slave craton, Northwest territories, Canada: A
preliminary review. Russian Geology and Geophysics 38 (1), 5 –16. Proceed-
ing of the Sixth International Kimberlite Conference Vol.1: kimberlites, related
rocks and mantle xenoliths. Allerton Press, New York.
Regis, A.J. and Sand, L.B. (1958) Natural cubic (b) silicon carbide. Geological
Society of America Bulletin, 69, 1633.
Schulze, D.J. (2001) Origins of chromian and aluminous spinel macrocrysts from
kimberlites in southern Africa. Canadian Mineralogist, 39, 361–376.
Stone, J., Hutcheon, I.D., Epstein, S., and Wasserburg, G.J. (1991) Correlated Si
isotope anomalies and large
13
C enrichments in a family of exotic SiC grains.
Earth and Planetary Science Letters, 107, 570–581.
Tang, M., Anders, E., Hoppe, P., and Zinner, E. (1989) Meteoritic silicon carbide
and its stellar sources; Implication for galactic chemical evolution. Nature, 339,
351–354.
Woermann, E. and Rosenhauer, M. (1985) Fluid phases and the redox state of Earth’s
mantle. Fortschritte der Mineralogie, 63, 263–349.
Zinner, E., Tang, M., and Anders, E. (1989) Interstellar SiC in the Murchison and
Murray meteorites: Isotopic composition of Ne, Xe, Si, C and N. Geochimica
et Cosmochimica Acta, 53, 3273–3290.
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