Seymchan is a pallasite meteorite found in the dry bed of the river Hekandue, a left tributary of river Jasačnaja in the Magadan district, Russia, near the settlement of Seymchan, in June 1967.
The main mass of 272.3 kilograms (600 lb.) was found during a survey in June 1967 by geologist F. A. Mednikov. The mass was a triangular-shaped thumb printed meteorite lying among the stones of the brook bed. A second specimen of 51 kilograms (112 lb.) was found with a mine detector at a distance of 20 m from the first in October 1967 by I. H. Markov. The main mass was turned over to the Academy of Sciences of the USSR.
Seymchan belongs to Main Group pallasites, but it is considered anomalous due to its high Ir content. Before the discovery of its pallasitic structure it had been classified as IIE anomalous coarse octahedrite. Seymchan is considered a stable and rust-resistant pallasite.
Due to the heterogeneous structure of Seymchan, there are two types of specimens: with or without olivine crystals. A Seymchan without olivine crystals is often referred to as a Seymchan Siderite due to is nearly exclusive iron content and a Seymchan with olivine crystals are referred to as a Seymchan Pallasite.
-- From Wikipedia