Although for 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.
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.
rusty (hematite) metal grain in Northwest
Africa 5000 (lunar). (Photo by Randy Korotev)
Rubin (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 mineral 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
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)
V. F. (1977) The
mineralogy of iron meteorites. Philosophical
Transactions of The Royal Society London A 286, 453–491.
286, 453–491. Geiger T. and Bischoff A. (1995) Formation
of opaque minerals in CK chondrites. Planetary and Space Science 43, 485-498.
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.
A. E. (1997a) Mineralogy of meteorite groups[RLK1] . Meteoritics & Planetary Science
A. E. (1997b) Mineralogy of meteorite groups: An update. Meteoritics
& Planetary Science 32, 733-734.
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