African Meteorites

Meteorites are rocky or metalliferous fragments that have been ejected from a body of the solar system following impacts with other bodies, and arriving on Earth after traveling more or less long in space. The majority of meteorites come from the asteroid belt (rocky bodies orbiting between Mars and Jupiter), and some other meteorites of lower frequency, can arrive from the Moon or the planet Mars. Meteorites provide information about the early stages of the evolution of our solar system in general and Earth in particular, as they contain information about protosolar and even presolar material. In this article, we will present an exhaustive synthesis of the formation and origin of meteorites, their categorization into “falls” and “finds” according to the circumstances of their discovery, the criteria for their identification, and the guidelines adopted for the nomenclature of meteorites falls and finds, and their classification.

Collecting meteorites just after their fall is a fundamental element to continue to gather information on the history of our solar system. During the period 1800-2020, 170 observed meteorite falls were recorded in Africa. The mass of fragments collected for any African meteorite range from 1.4 g to 175 kg, with a predominance of cases from 1 to 10 kg. The average rate of observed falls in Africa is low, with only one recovery per 1.29 years (i.e., 0.026 per year and per million km2 ). The African collection of observed falls is dominated by chondrites (84.4%), as in the world collection. The achondrites (10%) include three famous Martian meteorite falls: Nakhla (Egypt), Tissint (Morocco), and Zagami (Nigeria), whereas the observed iron meteorite falls are relatively rare (i.e., 5% of the collection). The rate of documented falls in Africa has been increasing since 1860, with 88% recovered during the period 1910-2020. Most of these falls have been observed and then collected in North-Western Africa, Eastern Africa and Southern Africa, in countries that feature a large area and a large but evenly distributed population. Other factors that are proven to be favorable to the observation and collection of meteorite falls on the African territory are a genuine meteorite education, the semi-arid to arid climate offering clear skies most of the time, cultivated land or sparse grassland and the possible access to the fall location favored by a low percentage of forest cover and a dense road network..

Africa is a favorable site for meteorite recovery, with a total number of recoveries amounting to more than 1/6 of all meteorites recovered from the entire world. This work deals with the classification of meteorite finds in Africa, the distribution of their masses, and their alteration/weathering grades as affected by various factors. The African meteorite population includes an abundance of stony meteorites with a high percentage of the world collection of rare meteorites, i.e., Martian meteorites (62%), Ureilites (51%), Rumuruti (59%), Lunar (47%), and HED (46%). Furthermore, an important increase in achondrite meteorites finds occurred in the last two decades, compared to the Australian and Antarctic collections. The mass distribution of the African meteorite population shows that most recoveries (72%) have masses bigger than 100 g with peaks of about 1 kg, compared to about 0.1 kg for the Australian collection and 0.01 kg for the Antarctic finds. The distribution of weathering grades (W) shows the predominance of W1 (32%) and W2 (34%), which proves a better preservation of meteorites in this continent. The factors influencing the mechanism and rate of alteration of African finds include climate as the main factor, the mass, the terrestrial age, and the initial porosity of the sample.

The number of meteorite finds in Northwest of Africa (NWA), i.e., Morocco, Algeria, Mauritania and Mali have recorded a considerable increase since 1999. However, the classification of these meteorites is done by the Meteorite Nomenclature Committee of the “Meteoritical Society”, only attributes 8% of the total finds of this region to their specific country of origin, and leaves 92% of them under the mere appellation “NWA” (Northwest Africa) followed by a number. This work attempts to contextualize the 5678 finds of NWA meteorites by defining the circumstances of the find of every sample, according to the new Categorization of Finds and the new Guidelines for Meteorite Nomenclature adopted by the Meteorite Nomenclature Committee. Thus, in addition to the 1180 official NWA meteorites whose countries of find are approved by the Nomenclature Committee, 3240 meteorites are assigned to 4 countries of North-West Africa, i.e., 2994 samples (92%) to Morocco, 79 samples (2.5%) to Algeria, 34 samples (1.1%) to Mauritania and 12 samples (0.1%) to Mali. Nevertheless, the remaining NWA meteorites (1267 samples) have no information indicating the country of finding. After the adoption of the naming “NWA”, we notice a remarkable decrease in the number of meteorites bearing the names of official places versus a considerable increase in the number of NWA meteorites. On the other hand, the statistical analysis of NWA meteorites reveals that the population includes rare specimens of great scientific value, making them highly desired by both scientists and collectors from all over the world. In general, this work results in the creation of a new database of meteorites stemming from the Northwest of Africa.

Since the first recorded discovery of a meteorite in 1937 near the Mrirt village, a total of 1747 authenticated meteorites have been recovered in Morocco. The collection includes 21 meteorites from authenticated observed falls, which comprise five different types of meteorites, i.e., 17 ordinary chondrites including four LL6, one EH7, one EH5, one H3-5, one H3-6, four H5, one CH, two L6 and two L4, one carbonaceous chondrite, one eucrite unbrecciated, one shergottite basaltic achondrites and one aubrite. The meteorite fall recovery rate in Morocco during the past 88 years (from 1932 to 2020) on a surface area of 712. 5 km2 is relatively low, with approximately four falls recorded every 10 years, equivalent to 0.4 falls per year per 2.11 km2 . A total of 1747 distinct and authenticated meteorite finds with a total mass of 6.175 kg have been described, which include 1674 stones (442 achondrites and 1232 chondrites), 37 iron, 24 stony-iron and 12 ungrouped meteorites. The rate of recovery of meteorites (falls + finds) in Morocco exceeds that of most other countries of similar size and climatic conditions. More than 95% of documented meteorites from Morocco, including many rare types, have been recovered from the Eastern Moroccan Sahara, which has been proven to be one of the most prolific world areas for meteorite finds.

The number of meteorites collected in the North African Sahara Desert is very relevant, as their conservation is facilitated by the dry climate, thus it represents one of the most important regions to recover rocks from space, along with Antarctica, Atacama and the great deserts of North America. However, more than 90% of the desert surface feasibly preserving important meteorites is estimated to be not yet explored. New finds are classified annually, and countries such as Mauritania, Mali and Egypt are emerging. The most optimistic forecasts suggest that many new meteorites will continue to be extracted from the great Sahara Desert in the coming decades. Collecting and preserving them properly is essential to bequeath to science such important research materials such as meteorites.

The aim of this chapter is to provide an updated review of the available data concerning the confirmed and proposed meteorite falls and finds and their impact craters in Egypt, Sudan, and Libya. Among the 190 confirmed impact/sites on the Earth crust, only less than 8 have been identified in northeast Africa, in particular, BP and Oasis in Libya and Kamil in Egypt. Very few other structures of alleged impact are located in these countries have been described in the literature. The record of meteorites and their impact craters in North East Africa are still incomplete and debated. The only criteria that provide evidence of an impact are the occurrence of circular geological features and their shock-metamorphic effects on the target rocks (shatter cones and diagnostic shock-metamorphic mineral deformations). These effects are evident in the Kamil crater (Egypt) and most impact craters in Libya. The discovery of preserved meteorite fragments and the detection of the geochemical signature of meteoritic indicators should be considered carefully during fieldwork and advanced further studies.