Meteorites in China

As would be expected, China has its share of meteorites. It is after all one of the oldest civilizations, with long records, and also China, however defined in its long history, is one of the world's largest countries. The Chinese meteorite trove has been documented (e.g., Bian, 1981). Chen and Wang (1994) provided an update: the earliest Chinese meteorite on record is Xiaxian of Shanxi province, which dates from 2,133 B.C. By 1911 there were 365 Chinese meteorite falls listed in the literature, but "unfortunately, few of these meteorites are preserved in collections", marking no doubt the turbulence of episodes of Chinese history from Antiquity to the mid-20th century.

Nantan (Nandan, Dongning, a 9.5-tonne IIICD) is the 2nd-largest iron known in China. Aletai (otherwise known as Xinjiang or Armanty, and other names) includes the first piece to be identified, the main mass "Armanty" from Xinjiang, which most likely was known before its official recognition in 1898.

Iron meteorites are classified by a combination of bulk chemistry of small samples (see, e.g., Malvin et al., 1984; Wasson et al., 1988), and the textures seen in polished and etched surfaces. Analyses (by the favoured method of INAA, instrumental neutron activation analysis) of 15 samples of Armanty yielded mean assay values such as 230 ppb Ir, 2.3 ppm Pt, 1.83 ppm Au and 9.76% Ni (Wasson et al., 1988).

The IIIE irons are an uncommon group, with just 19 known examples (Meteoritical Bulletin, 08 February 2025). They often contain haxonite, a Ni-Fe carbide, in areas of plessite (a fine kamacite-taenite intergrowth in the metal). Armanty, along with Coopertown, Staunton and some other examples, appear to have suffered only weak shock since their crystallization from a nickel-iron melt on their parent body (Breen et al., 2016). The composition of Armanty is quite homogeneous, suggesting minimal magmatic fractionation (Wasson et al., 1988). Other minerals include the carbide cohenite and the phosphide schreibersite.

Aletai iron meteorite shower

It is not uncommon for meteorites to be found as single masses, and later expeditions to recover additional, perhaps even greater masses (e.g., Seymchan, Campo del Cielo). Sometimes it is found in hindsight that finds from different localities may be "paired", i.e., came from a single fall. The smaller (430 kg, so not "small"!) Ulasitai iron meteorite, recognized by a geologist in 2004, is quite probably paired with Armanty in this manner (Xu et al., 2008). Indeed the original 28-T Armanty mass, Ulasitai and other irons are now thought to be of a single fall, the whole referred to as Aletai. The history is explained in an entry for Aletai in the Meteoritical Bulletin. The total known mass is now some 74 tonnes, along a remarkably, perhaps uniquely long (425 km) strewnfield along and generally just south of the modern border of Xinjiang with Mongolia (Xu et al., 2008, provide a location map for the Ulasitai and Armanty irons). Such a disposition of fragments, as large as 28 and 23 tonnes, implies that the iron meteoroid approached Earth and entered the atmosphere at a very shallow angle, a grazing incidence. One wonders if this is analogous to the "Chant Trace" of 1913, well-known to astronomers, and beautifully described at the time of the event (see footnote below).

This large iron has been studied from a number of perspectives. The distribution of helium and neon isotopes as a function of depth (Leya et al., 2010; Ammon et al., 2011) provides an estimate of the production of cosmogenic radionuclides, generated in space where the meteoroid is subject to a flux of both solar and galactic cosmic rays.

A survey of the metallographic textures and mineralogy of IIIE irons (Breen et al., 2016) classified a number of irons according to the severity of shock effects. The least shocked irons included Armanty, Coopertown and Staunton (haxonite in plessite, and unrecrystallized kamacite with Neumann lines or epsilon structure, the sulphide inclusions of polycrystalline troilite with daubreelite exsolution lamellae). Increasing shock results in haxonite part decomposed to graphite, most kamacite recrystallized, and sulphide inclusions part-melted. Severe shock is marked by the occurrence of graphite but no haxonite, kamacite recrystallized, troilite melted. There may be sulphide-rich assemblages with fragmental to subhedral daubreelite, spidery troilite filaments, and low-Ni kamacite with up to 6 wt.% cobalt.

The past 20 years have seen a rapid rise in the use of non-destructive, hand-held instrumentation to provide guidance in the field, for diverse purposes in mineral exploration, metallurgy and recycling. An example is LIBS (laser-induced breakdown spectroscopy). LIBS was recently tested on 19 iron meteorites, the LIBS results showing generally good agreement with established laboratory methods for elements such as Fe, Ni, Co, Cu and Ga (Senesi et al., 2024). The test samples included Aletai and other well-known irons such as Campo del Cielo, Dronino, Gebel Kamil, Mount Dooling, Saint-Aubin and Maslyanino, all of which can be found in these "Rock of the Month" pages!

Footnote on grazing-incidence fireball events

In 1913, a succession of short-lived fireballs was noted across North America and out into the Atlantic ocean. Professor Clarence A. Chant, then in Toronto, made the first compilation and estimation of the events, a series of notes extended by others, including Alexander Mebane. The phenomenon became known as the Chant Trace or the "Cyrillids" (a nod to meteor showers). Records have been compiled and interpreted over the century since the dramatic sightings (e.g., Mebane, 1956; Ricker and Schnute, 1999). Most are from Canada and the northern U.S.A., the complete span of sightings extending from just north of Vancouver Island, eastward and south past towns and cities such as 100 Mile House (British Columbia). Regina (Saskatchewan), Hibbing (Minnesota), Houghton (Michigan) and Toronto (Ontario), ending in the Atlantic ocean, south of the equator, off the coast of Brazil. More recently the fall has been likened to the decaying orbit of a satellite on course to re-enter the atmosphere, and one explanation is the fall of a "minimoon", a dm- to m-scale meteoroid that has fallen into a temporary orbit around Earth, and is subsequently pulled inward to (generally) burn up in the atmosphere (Olson and Hutcheon, 2013).

REFERENCES

Ammon,K, Leya,K and Lin,Y (2011) Noble gases in the Xinjiang (Armanty) iron meteorite - a big object with a short cosmic-ray exposure age. Meteoritics & Planetary Science 46, 785-792.

Bian,D (1981) Chinese meteorites. Meteoritics 16, 115-128.

Breen,JP, Rubin,AE and Wasson,JT (2016) Variations in impact effects among IIIE iron meteorites. Meteoritics & Planetary Science 51, 1611-1631.

Chen,Y and Wang,D (1994) An update of a catalog of Chinese meteorites. Meteoritics 29, 886-890.

LeMaire,TR (1980) Stones from the Stars: The Unsolved Mysteries of Meteorites. Prentice-Hall, Inc., 185pp.

Leya,I, Ammon,K and Lin,Y (2010) Noble gases in the Xinjiang (Armanty) iron meteorite - a big object with a short cosmic-ray exposure age. Meteoritics & Planetary Science 45, A118.

Malvin,DJ, Wang,D and Wasson,JT (1984) Chemical classification of iron meteorites-X. Multielement studies of 43 irons, resolution of group IIIE from IIIAB, and evaluation of Cu as a taxonomic parameter. Geochimica et Cosmochimica Acta 48, 785-804.

Mebane,AD (1956) Observations of the great fireball procession of 1913 February 9, made in the United States. Meteoritics 1 no.4, 405-421.

Olson,DW and Hutcheon,S (2013) The great meteor procession of 1913. Sky & Telescope, 32-34, February.

Ricker,WE and Schnute,JT (1999) A westward trajectory extension for the Earth-grazing fireballs seen on 9 February 1913. Canadian Field-Naturalist 113, 693-697.

Senesi,GS, De Pascale,O, Mattiello,S, Moggi Cecchi,V, Ibhi,A, Ouknine,L and Nachit,H (2024) Recent advances in the compositional and mapping analysis of iron meteorites using a handheld laser-induced breakdown spectroscopy instrument. Geostandards and Geoanalytical Research, 26pp.

Wasson,JT, Ouyang,X and Wang,D (1988) Compositional study of a suite of samples from the 28-t Armanty (Xinjiang) iron meteorite. Meteoritics 23 no.4, 365-369.

Xu,L, Miao,B, Lin,Y and Ouyang,Z (2008) Ulasitai: a new iron meteorite likely paired with Armanty (IIIE). Meteoritics & Planetary Science 43, 1263-1273.