The chondrite Mihonoseki: New observed fall

On 10 Dec. 1992, 21:00 hours Japanese standard time, a stone weighing 6.385kg, struck a two-story house in Mihonoseki-machi, Yatsuka-gun, Shimane-ken, Japan, 35 deg 34.1 min N, 133 deg 13.2 min E. Through petrographical and mineralogical examination and rare gas analysis, the meteorite was classified as an L6 chondrite. The preatmospheric chondrite is rather small in size (Ne-22/Ne-21 = 1.180 and extremely low Co-60 activity), and shocked features are not distinct. Cosmic-ray exposure ages obtained from He-3, Ne-21, and Ar-38 are 61 m.y., and K-40/Ar-40 age is 4.41 b.y. Measurements of cosmogenic radioactive nuclides and chemical analyses are now proceeding.