Some Meteorite Statistics

Where Are Meteorites Found?

Nearly all meteorites are found in deserts. (Yes, Antarctica is a desert because the annual precipitation rate is very low.) Deserts are places that accumulate meteorites over thousands of years and then nothing much happens to the meteorite. Also, meteorites are easier to find in deserts than in places with topography, vegetation, and other rocks.

Figure 1. More meteorites have been found in Antarctica than all other continents combined. “Island nations” includes The United Kingdom, Ireland, Greenland, Madagascar, Sri Lanka, Japan, Philippines, Indonesia, Papua New Guinea, New Zealand, and Cuba.
Figure 2. About two thirds of meteorites found in the United States have been found in arid regions of California, Nevada, Arizona, New Mexico, Texas, and Kansas. 2200 meteorites have been found in Chile, mainly in the Atacama Desert.
Figure 3. “Saharan” Africa includes the northern Africa countries of Morocco, Western Sahara, Mauritania, Mali, Algeria, Tunisia, Libya, Niger, Chad, Egypt, and Sudan. “Sub-Saharan is everything to the south. Most meteorites (96%) from the Arabian Peninsula were found in Oman. Central Asia includes Kazakhstan, Uzbekistan, Kyrgyzstan, Tajikistan, and Afghanistan. Southwest Asia is Azerbaijan, eastern Turkey, Syria, Lebanon, Jordan, Israel, Iraq, and Iran. South Asia is Pakistan, India, and Bangladesh. Southeast Asia includes Myanmar, Thailand, Malaysia, Laos, Cambodia, Vietnam, North Korea, and South Korea.

Nearly 42,000 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. Over 14,000 meteorites have been found in the Sahara Desert of northern Africa, most since 1995, mainly by nomads and private collectors. About 4200 have been found on the Arabian Peninsula, mostly in the Sultanate of Oman, a desert country about the size of New Mexico.

Figure 4. This diagram present mass proportions. Compare with Fig. 1.

The geographic distribution of meteorites is considerably different if calculated by mass instead of by number (Fig. 4). 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 55 g (about 2 ounces), compared with 248 g (about a pound) for meteorites from the Sahara where little ones are easier to miss. (The smallest 90% of meteorites from Antarctica average only 17 g in mass.) Some of the other slices of Fig. 4 are much larger than in Fig. 1 because of massive iron meteorites from China (Aletai, 74 tons), Namibia (Hoba, 60 tons, and Gibeon, 26 tons), Greenland (Cape York, 58 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 (391.5 metric tons) account for 56% of the mass of all known meteorites.

Finds and Falls

Only a small fraction of collected meteorites have been observed to fall, 1.8% for the whole world. “Observed” usually means that a meteor was seen or heard and the stone or stones causing the effects was recovered shortly thereafter, usually within a few days. Such meteorites are called “falls” by meteoriticists. The other 98% are called “finds” – someone found the meteorite but the meteor was not observed.

Figure 5. By number, the proportion of meteorites from North America that are falls is greater than that for the whole world because most meteorites have been found in Antarctica (Fig. 1) yet there has never been an observed fall there. Meteors over North America that yield meteorites are usually seen by many people and there active efforts to recover any fragments of the meteorite that land on Earth.
Figure. 6. By mass, the proportion of falls is about the same for North America and the whole world.

Stony and Iron Meteorites

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.

Figure 7. Most meteorites that have been observed as falls are stony.
Figure 8. The difference between these two plots reflects that (1) the massive Sikhote Alin iron meteorite (23 metric tons, most of the red pie slice on the left) fell in Russia in 1947, (2) there have only been 5 falls of iron meteorites in North America and none has been large (largest: Cabin Creek, Arkansas, 1886, 48.5 kg), and the only mesosiderite observed to fall in North America (Estherville, Iowa, 1879) was fairly large (320 kg). No pallasites have been observed fall in North America.

In populated places like North America, however, people find (Fig. 9) a greater fraction of irons than the fraction of irons among falls (Fig. 7) because irons tend to be more massive and are more likely to catch peoples’ attention. Many have been found by farmers plowing a field.

Figure 9. Iron meteorites probably survive longer in temperate environments than do stony meteorites such as chondrites.
Figure 10. Among all recovered meteorites, most of the mass, 83.5%, is carried by iron meteorites. The proportions are similar for North America and the whole world.

Types of Stony Meteorites

Most stony meteorites (93.1%) are chondrites, and most chondrites (93.9%) are ordinary chondrites. Put another way, 87% of stony meteorites are ordinary chondrites.

Figure 11. Relative abundances of stony meteorite types by number.

Chondrites contain iron-nickel metal, which is what makes them attract a magnet. Most other stony meteorite types contain little metal. The rare achondrites (6.9%) 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 cannot tell the difference just “by looking.”

Figure 12. Relative abundances of stony meteorite types by mass.

The picture is a bit different when measured by mass. The aubrite slice is much larger here than in Fig. 11, because among the 93 enstatite achondrites (aubrites), one is huge, Norton County (1.1 metric ton). Similarly, the enstatite chondrite field is bigger in the mass diagram because of huge Al Haggounia 001 (3 metric tons).

Antarctica vs. Northern Africa

Figure 13. In northern Africa, the proportion of rarer types (= not ordinary chondrites) of stony meteorites is nearly 5 times greater than in the Antarctic collection.

As noted above, in Antarctica icefields are searched systematically and all meteorites are collected. I suspect that in northern Africa, most meteorites that are found are actually collected. On the basis of Fig. 13, however, I suspect that many of the ordinary chondrites are not classified and, consequently, are not listed in the Meteoritical Bulletin Database. Unclassified NWA chondrites are avaialble for sale on the internet for less than a dollar per gram.

I gleaned all data presented here from the Meteoritical Bulletin Database of The Meteoritical Society. Thanks, Jeff.