Iron, IC, octahedrite
standby for arispe photo
Found 1896
30° 20' N., 109° 59' W.

Two masses of 116 pounds and 20 pounds were found about 25 miles NW of Arispe, Sonora, Mexico. In 1898, another mass weighing 272 pounds was discovered 15 miles NW of Arispe and was sectioned and distributed to several museums. In the years following, many more masses were recovered along a 12-mile line from Mount San Antonio to Arispe. At least sixteen individuals with a total weight of over 1,500 pounds show that the Arispe shower was a significant one.

Arispe is a polycrystalline iron meteorite with distinctly oriented austenite crystals up to 25 cm in diameter. Troilite inclusions occur throughout, enveloped by schreibersite. The compositional trends are most consistent with formation from a residue of equilibrium partial melting. While distantly related to group IA irons, its lower Ni content of 6.1%–6.8% led to the establishment of a new group, IC. A unique feature present among group IC members is the occurrence of abundant cohenite and other carbon inclusions. Due to a high iridium content, Arispe is considered an anomalous member of the diverse IC group. Radioisotope chronometry indicates an unusually long terrestrial age for the Arispe masses of 240,000 (±50,000) years.

The above specimen is an etched 39.6 g partial slice. A photo of the complete 1898 mass weighing 272 pounds is shown below. To learn more about the relationship between this and other iron chemical groups, click here.

standby for arispe photo