Some Meteorite Statistics
Nearly all meteorites are found in deserts. (Yes, Antarctica is a desert because the annual precipitation rate is very low.) Deserts are places that collect meteorites over thousands of years and nothing much happens to the meteorite. Also, meteorites are easier to find in deserts then in places with lots of vegetation or other rocks.
Nearly 37,000 meteorites have been found in Antarctica by government funded expeditions, mainly by the U.S. and Japan. Nearly all of these have been found since 1976. About 10,000 meteorites have been found in the Sahara Desert of northern Africa, most since 1995, mainly by nomads and private collectors. About 4000 have been found on the Arabian Peninsula, mostly in the Sultanate of Oman, a desert country about the size of New Mexico.
The geographic distribution of meteorites is considerably different if calculated by mass instead of by number. The field for Antarctica shrinks considerably. In Antarctica, all meteorites in a search area are collected regardless of size. Thus, the average mass of meteorites from Antarctica is 154 g, compared with 2420 g for meteorites from the Sahara where little ones are easier to miss. (The smallest 90% of meteorites from Antarctica average only 25 g in mass.) The North America and “everywhere else” slices are much larger because of massive iron meteorites from Namibia (Hoba, 60 tons, and Gibeon, 26 tons), Greenland (Cape York, 58 tons), China (Aletai, 50 tons), Argentina (Campo del Cielo, 50 tons), U.S. (Canyon Diablo, 30 tons), Mexico (Chupaderos, 24 tons, and Bacubirito, 22 tons), Australia (Mundrabilla, 24 tons), and Russia (Sikhote-Alin, 23 tons. Together, these 10 meteorites (367.5 metric tons) account for 54% of the mass of all known meteorites.
Only a small fraction of meteorites have been observed to fall, 2.0% for the whole world. These meteorites are called “falls” by meteoriticists. The other 98% are called “finds.” By number, the proportion of meteorites that are falls from North America is greater than that for the whole world because most meteorites come from the deserts, places where meteorites are rarely observed to fall because there are so few people. Also, nearly all meteorites from deserts fell long before humans actively sought them.
If only Falls are considered, most meteorites are stony meteorites. Only a few percent are iron meteorites, also known as “irons.” Mesosiderites and pallasites are rare types of meteorites that contain subequal volumes of both metal and stony material.
In populated places like North America, however, people find a greater fraction of the irons because irons tend to be more massive and are more likely to catch peoples’ attention. Many have been found by farmers plowing a field.
Most of the mass of meteorites striking Earth, 85%, is carried by iron meteorites. The proportions are similar for North America and the whole world.
The mass proportions are considerably different when only falls are considered. For the whole world, I suspect that among finds, the mass proportion of iron meteorites is greater than among falls because large iron meteorites survive longer on Earth than do stony meteorites. (If someone knows more about this than me, please correct me.) For North America, the iron wedge is small because there have been only 6 falls of iron meteorites, the largest of which (Cabin Creek, Arkansas, 1886) is only 48.5 kg in mass.
Most stony meteorites (94.1%) are chondrites, and most chondrites (94.3%) are ordinary chondrites. Put another way, 89% of stony meteorites are ordinary chondrites. Chondrites contain iron-nickel metal, which is what makes them attract a magnet. Most other stony meteorite types have little metal. The rare achondrites (5.9%) resemble Earth rocks more closely than do other meteorite types. It usually requires chemical or mineral analysis to determine if a rock is an achondrite. In the absence of a fusion crust, most of us can’t tell the difference just “by looking.”
The picture is a bit different when measured by mass. The enstatite achondrite slice is much larger here than on the “by number” chart, because among the 87 enstatite achondrites (aubrites), two are huge, Norton County (1.1 metric ton) and Al Haggounia 001 (3 metric ton).
As noted above, in Antarctica icefields are searched systematically and all meteorites are collected. On the basis of this chart, I suspect that in hot deserts (Sahara and Oman), most found meteorites are collected, but that many of the ordinary chondrites are not classified and, consequently, are not listed in the Meteoritical Bulletin Database. Thus, the proportion of achondrites (which are more valued by collectors) among stony meteorites stated above, 5.9% by number, is an overestimate. Among Antarctic meteorites, only 4.0% of stony meteorites are achondrites.
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