convenience we sometimes state here that the minerals quartz, calcite, magnetite, hematite, and micas do not occur in
meteorites, these statements are not entirely true. Each of these minerals
are among the many minerals listed by Rubin (1997a,b) and Rubin and Chi
(2017) that have been observed in some meteorites. However, all these
minerals are minor to rare in any type of meteorite and don’t occur
naturally at all in the most common types of meteorites.
There is no
type of meteorite in which quartz would be evident without the aid of a
petrographic microscope and a petrographic thin section. It takes skilled
petrographers considerable effort to find and identify silica minerals in
meteorites. With regard to quartz, Rubin (1997a) mentions it only in the
discussion of enstatite chondrites, eucrites, and basaltic shergottites,
all rare types of meteorites. Enstatite chondrites and eucrites contain
minor amounts (a few percent, at most) of free silica (tridymite, cristobalite, and quartz). Less than 1% of all
known meteorites are enstatite chondrites and <1% are eucrites. In the
basaltic shergottites (~0.05% of meteorites, but quartz has only been
reported from a few), it is an accessory mineral (<1% of volume). (See
in the Mars
Meteorite Compendium.) Some other achondrites contain trace amounts of
the silica polymorphs, tridymite and cristobalite. If you can see quartz
with the naked eye, then the rock is not a meteorite. The standard field test
for quartz is the scratch test
Magnetite and hematite are oxides of iron.
Magnetite occurs as a trace to minor mineral in several kinds of
meteorites. Rubin (1997a) states that it is the “principal oxide phase in
the CK chondrites,” a rare type of meteorite (0.3%). Geiger and Bischoff
(1995) found that the modal abundance of magnetite ranged from 1% to 8% in
the 19 CK chondrites that they studied. Thus, a large CK chondrite with 8%
magnetite might deflect a compass needle.
hematite blueberries have not been reported in martian meteorites, grains
of hematite do occur” (Rubin and Chi, 2017). Hematite does not occur naturally
in other meteorites, but occurs in many meteorites, e.g., iron finds (Buchwaldt (1977) as a terrestrial weathering product.
Iron rust is mainly hematite. Most meteorites contain iron metal. That metal will begin to rust soon after the
meteorite falls. Any meteorite that looks rusty or has reddish staining
probably contains some hematite, but a freshly fallen meteorites will not
contain hematite. Not all hematite is rusty colored; some is gray. The
standard field test for hematite is the streak test.
A rusty (hematite) metal grain in Northwest Africa
5000 (lunar). (Photo by Randy Korotev)
(1997a) states that "Carbonates occur as veins and aggregates in CI
chondrites; the aggregates probably formed from fragmented carbonate veins.
The principal phases are ferroan magnesite, siderite, dolomite, and pure
calcium carbonate (vaterite and/or calcite);" references are given. As
of December 1999, there were only 5 CI chondrites known among more than
22,000 meteorites cataloged by Grady (2000). Rubin (1997a) also states that
"Phyllosilicates [e.g., micas] occur in the matrix and the interiors
of chondrules... Associated with the phyllosilicates are Ca-carbonates and
magnetite." Again, however, these minerals occur in very small
quantities. Some meteorites may contain minor calcite as a result of weathering
on Earth. This calcite might be evident in veins upon hand inspection.
The vein-filling white material on the right-hand side of
this photo of Northeast
Africa 001 (lunar) is nearly pure calcite from terrestrial weathering.
(Photo by Randy Korotev)
Buchwald V. F. (1977) The
mineralogy of iron meteorites. Philosophical
Transactions of The Royal Society London A 286, 453–491.
A 286, 453–491. Geiger T. and Bischoff A. (1995) Formation
of opaque minerals in CK chondrites. Planetary and Space Science 43, 485-498.
Grady M. M. (2000) Catalogue of Meteorites, With special
reference to those represented in the collection of the Natural History
Museum, Fifth Edition, Cambridge
University Press, Cambridge, 689 pp and CD-ROM.
Rubin A. E. (1997a) Mineralogy
of meteorite groups. Meteoritics & Planetary Science 32, 231-247.
A. E. (1997b) Mineralogy of meteorite groups: An update. Meteoritics
& Planetary Science 32,
Rubin A. E. and Chi M. (2017) Meteoritic
minerals and their origins. Chemie der Erde – Geochemistry, http://dx.doi.org/10.1016/j.chemer.2017.01.005