MIAC

Stony Meteorites

Holbrook.

This L6 olivine-hypersthene chondrite fell in 1912 in Navajo County, Arizona, as part of a shower of stones estimated to be made up of as many as 14000 individuals, ranging in mass from 6.6 kg downward and with a total mass of about 218 kg. The slide shows an individual with typical black fusion crust with well marked flow lines. These furrows, which are formed by the atmospheric ablation of the meteorite, are deepest on the forward surface and radiate away from the apex. The incomplete nature of the fusion crust indicates that this sample is from a meteorite that broke apart as it struck the ground. (Photo courtesy Geological Survey of Canada)


Bruderheim.

The largest recovered fall in Canada, Bruderheim was located and collected after a spectacular fireball was seen over a wide area on the 4 th march, 1960. It has been widely studied by modern techniques of isotopic, trace element and electron microprobe analysis. It is a L6 chondrite. (Photo courtesy Geological Survey of Canada)


Sample locations of meteorites of the Bruderheim fall.

The brilliant fireball that was observed for the Bruderheim fall ended with a detonation that was heard over about a 100 km radius. Pieces were quickly located lying on the surface of the snow, ranging in size from a few milligrams to 31 kg. In total, nearly 700 fragments with a total mass of more than 303 kg were recovered from an area which was centred about 10 km north of the town of Bruderheim. The largest individual is in the National Meteorite Collection, Ottawa, although the bulk of the material is held at the University of Alberta in Edmonton. The slide shows the approximate ellipse of fall as defined by recovered fragments. Note that the fireball was traveling in an WNW to ESE direction and that the larger fragments are concentrated at the far end (ESE) of the ellipse.

Fragments of the Bruderheim fall.

The stones making up the Bruderheim fall vary enormously in size from 31 kg downwards. The slide gives some idea of this size range. It will be noted that virtually all the fragments show the typical black fusion crust, indicating that fragmentation took place during the passage through the atmosphere while the meteor was still traveling fast enough to cause frictional surface fusion. The largest piece of such a shower tends to travel furthest and thus end up towards the end of the ellipse of fall furthest from the radiant of the fireball. (Photo Dr. Peter Millman).


Abee - Cut surface.

This meteorite was discovered in a wheat field near Abee, Alberta shortly after it fell on June 9, 1952. With a mass of about 107 kg, the meteorite produced a hole about 75 cm in diameter, nearly 2 m deep and at angle of 65° to the horizontal. The meteorite is a relatively rare E4 enstatite chondriteand is seen in the slide in a polished slab. Abee is a black breccia made up of clasts (many rimmed by kamacite/taenite), dark inclusions and matrix. It has proved to be of great scientific interest and an international 'consortium' of scientists and laboratories was established to investigate the meteorite using modern isotope and microanalytical techniques. Refs. P. Millman, J. Roy. Astron. Soc., Canada, 1953, v.47, p. 32; Earth & Planetary Science Letters, v. 62, p. 116 et.seq). (Photo courtesy Geological Survey of Canada)


Catherwood - Cut surface.

This meteorite was found on a farm at Catherwood, southwest of Saskatoon by a Mr. Cecil Rolls, after it became entangled in a rod weeder, probably in 1965. It eventually found its way via a rock collector to the MORP headquarters in Saskatoon and the main mass is now in the Canadian National Meteorite Collection. It is a common L6 chondrite but is interesting because of the well developed glassy, black shock veins which are clearly visible in the slide. These have been shown to contain the minerals ringwoodite and majorite, ultra-high pressure equivalents of olivine and Ca-pyroxene, respectively. (Ref. L.C. Coleman,1977: Canadian Mineralogist v. 15, p. 97-101) (Photo courtesy Geological Survey of Canada)


Allende.

This meteorite from the well known Chihuahua district of Mexico fell on February 8, 1969 after a bright bolide was seen in the very early hours of the morning. It turned out to belong to the relatively rare class of meteorites, the carbonaceous-chondrites (CV3), and was found in a strewn field estimated to cover more than 150 km. More than two tons of the meteorite have been collected in hundreds of fragments, the largest of which had a mass between 100-110 kg but unfortunately broke up on impact. The sample seen in the slide shows remnants of the black fusion crust produced during the meteorite's passage through the atmosphere, as well as the typical interior colour of carbonaceous chondrites. Compare the broken surface here with that of the ordinary chondrite (Innisfree) above. (Ref. E.A. King et al., 1969, Science, v. 163, p. 928)  (Photo courtesy Geological Survey of Canada)


Allende - detail.

The slide shows a close up view of a broken surface of Allende. Several features are worthy of note: the overall colour is much darker than that typical of ordinary chondrites. Metal particles (kamacite) are very rare but nearly spherical chondrules are common. Also apparent are some white coloured patches or 'aggregates'. Allende has been the subject of intense study and has revealed an extremely complex mineralogy. The white-coloured Al-rich aggregates, it was suggested, are nebular condensates. More recently interest in them has been further stimulated by the demonstration that they contain oxygen and other elements with anomalous isotopic compositions, suggesting that they may contain extra-nebular material that predates the formation of our solar system. (Photo courtesy Geological Survey of Canada)


Riverton - section of a chondrule.

Chondrules, nearly spherical bodies typically a millimetre or less in diameter, are essential constituents of all chondritic meteorites, although their abundance varies greatly from one meteorite to another. Theories about their origin have varied widely and they have been variously attributed to condensation, melting by lightning, impact or friction, and even to explosive volcanism. The chondrule seen in the slide is made up largely of plates of olivine and is essentially crystalline. Others, however, may be made up of orthopyroxene, or mixtures of several minerals, including sulphides. Chondrules may be very fine grained or even totally glassy in meteorites that have suffered little or no reheating ('metamorphism'). Riverton, in which the figured chondrule occurs, is a small H5 chondrite found in 1960 or 1961 near the town of Riverton, Manitoba. Its mass is only 103 g and it was not recognised as a meteorite until 1968. One piece of 24.8 g is now in the Canadian National Meteorite Collection, Ottawa. (Photo courtesy Geological Survey of Canada)



Tektite.

Although at one time thought by many scientists to be extraterrestrial objects, tektites are now generally believed to be formed from terrestrial material melted by a major impact and ejected into the upper atmosphere. Individual tektites range in size from a few centimetres in diameter downwards and vary greatly in shape with button-like, tear drop and dumb-bell shapes being the most common. The objects show evidence of having travelled a great distance from the point of impact, perhaps halfway around the world. The button shapes are due to frictional ablation of originally more spherical bodies. Microtektite concentrations have been found in deep sea sediments. The tektites in the slide are probably indochinites from the Australiasian strewn field. (Photo courtesy Geological Survey of Canada)



Meteor-wrongs - slag.

Many different materials are frequently mistaken for meteorites. The most common meteor-wrongs vary with the region of the country. In the Prairies, for example, clay ironstone nodules are frequently taken to be meteorites. Slag from soil burned in clearing land and cinder-like aggregates from burning old straw stacks are also often thought to be of meteoritic origin, because they are so different from local rocks. For the same reason, glacial erratics are commonly submitted for inspection as potential meteorites. (Photo courtesy Geological Survey of Canada)



More images of meteorites are available at: Nine-planets

Authored by the MIAC Slide Group and Michael Higgins