Mesosiderite, group 1B
standby for chinguetti photo
Found 1916
20° 15′ N., 12° 41′ W. In 1916, a French Legion captain named Gaston Ripert, along with his Arab guide, led his soldiers through the Western Sahara Desert in the Adrar region of Mauritania. His guide brought him to a giant metallic meteorite mass, said to have been the source of iron for Arab blacksmiths. Smaller masses were scattered about the area, one of which, weighing 4.5 kg, was collected from on top of the giant mass. Capt. Ripert had no map, compass, or measuring stick, and was only able to make very cursory observations. According to his later recollections, the find location was about 10 hours by camel to the southeast of Chinguetti, among the dunes of Ouarane (in earlier transcribed notes, the location was said to be about 45 km to the southwest of Chinguetti and to the west of Aouinet N’Cher). The large metallic mass was described as measuring 100 m in width and 40 m in height, with one side polished by the wind into a mirrored finish. The base was deeply carved by the wind, and metallic, needle-like projections covered the summit of the mass; these projections could not be removed by their best efforts.

Many subsequent expeditions to the area, particularly those by Théodore Monod, Directeur de l’Institut Francaise d’Afrique Noire in Paris, failed to locate any sign of this giant meteorite among the dunes. It was therefore assumed that Capt. Ripert had misidentified a blackened, quartzite–sandstone rock outcropping as the main mass from which the smaller fragments were cleaved. However, Capt. Ripert remained steadfast in his story throughout his life.

Modern radiometric dating techniques have been applied to this mystery to determine the CRE age, terrestrial age, and the pre-atmospheric size of the 4.5 kg Chinguetti mass (Welten et al., 2001). Methods employed have established a CRE age of 66 (±7) m.y, similar to that of the Estherville and Crab Orchard mesosiderites. The terrestrial age was calculated to be less than 18 (±1) t.y, a relatively short interval which is inconsistent with the description given by Capt. Ripert—that of a mass having a deeply wind-carved base. Perhaps most importantly, the pre-atmospheric diameter of Chinguetti was determined to be only ~1.2 m given a shielding depth of ~15 cm, which calls into serious doubt the existence of the giant meteoritic mass.

Based on the metamorphic textures of matrix silicates, the mesosiderites were assigned to specific subgroups (Powell, 1971; Floran, 1978, Hewins, 1984), with Chinguetti being assigned to the least metamorphosed subgroup-1. In his scheme, Hewins proposed a further division of the least metamorphosed category based on plagioclase abundance: a higher abundance for group 1A (24%) and a lower abundance for group 1B (21%). Visit the Bondoc page for a more thorough description of this grouping scheme. The photo above shows a 0.58 g micromount of this very rare mesosiderite. A more representative photo of Chinguetti exhibited at the Muséum National d’Histoire de Paris can be seen at their website.

See also the online article by Richard Greenwood (2014), ‘The meteorite that vanished’.

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