|Tucson Ring Meteorites|
Two masses of the Tucson meteorite were found in 1850, but native people must have known about these masses of iron for centuries before that. One was the ring-shaped Irwin-Ainsa mass, the second the paired, bean-shaped, Carleton mass. The meteorites consist of 92% iron with 8% silicate inclusions, which is very high for an iron meteorite. Tucson may be the result of an impact between an iron asteroid and a stony asteroid. The parent body of the Tucson meteorite cooled rapidly, so there is no Widmanstätten pattern present. The Tucson meteorite is classified as an ungrouped ataxite iron with silicate inclusions.I took this photo in the Smithsonian Institution National Museum of Natural History NMNH.
Each of the Tucson masses has its unique history. The first recovered and the larger of the two is the 688 kg ring-shaped mass, also called the Ring or Signet, Ainsa and Irwin-Ainsa Meteorite at various times in history: The earliest account of the meteorites is by a Sonoran official, Jose Francisco Velasco, who says several iron masses were found between Tucson and Tubac, in Puerto de los Muchachos and at the foot of Sierra de la Madera. One mass, he said, was taken to Tucson. Later, the second known mass, Carleton, was also transported from the mountains to Tucson. Both masses had been used as anvils in blacksmith shops.The Mexican troops left Tucson in 1856, leaving behind the famous meteorites. In 1860, the Smithsonian Institution asked Lieutenant Irwin, an army physician and amateur naturalist in the area, to go to Tucson to recover the Tucson Ring meteorite. He found it, pulled it out of the ground, and entrusted it to a man who was to go to the coast and deliver it by ship to the museum. The man carried out his mission, but told the Smithsonian that his great-grandfather had discovered the meteorite. The family name, Ainsa, was given to the meteorite. Irwin attempted for many years to re-establish the truth before the deception was finally recognized.