8 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 124 



The Cynthiana Meteorite 



This meteorite fell about 4 p.m. on Jan. 23, 1877, after a brilliant 

 fireball was seen over a considerable region of southern Indiana and 

 northern Kentucky. The place of fall was in Harrison County, Ky., 

 about 9 miles from the town of Cynthiana. It is remarkable that this 

 was the third meteorite fall in the Middle West within a month's 

 span, the others occurring in Rochester, Ind., on Dec. 21, 1876, and 

 Warrenton, Mo., on Jan. 3, 1877. 



A single stone weighing 6 kg was recovered; it was described and 

 analyzed by Smith (1877). He commented on its brecciated appearance 

 and remarked that in this and other characteristics it resembled the 

 Parnallee meteorite. Urey and Craig (1953) rejected Smith's analysis 

 because of the very low A1 2 3 content shown therein. Because of this, 

 we decided to reanalyze the meteorite, using a piece from the specimen 

 (no. 748) in the U.S. National Museum. 



MlNERALOGICAL COMPOSITION AND STRUCTURE. A Cut Surface of 



the meteorite is medium gray in color with prominent chondrules, 

 some lighter and some darker than the groundmass. Many of the 

 chondrules show dark rims; occasionally one sees a dark chondrule 

 with a light-colored rim. A moderate amount of metal and troilite is 

 scattered through the groundmass, some of the grains being unusually 

 large, from 2 to 3 mm across. The brecciated structure commented on 

 by Smith is not especially prominent in our hand specimen. The stone 

 is remarkably fresh, the broken surfaces showing no sign of limonitic 

 alteration after nearly a century of exposure to the atmosphere. 



The principal minerals are olivine and pyroxene. Troilite and nickel- 

 iron are present in minor amounts. Plagioclase was not certainly 

 identified optically although rare grains with a refractive index of 

 about 1.54 and a low birefringence were seen in an acid-insoluble 

 fraction of the meteorite; a very weak peak corresponding to feldspar 

 was seen in an X-ray diffractogram. Accessory minerals include chro- 

 mite and a phosphate (apatite or merrillite, or both). 



Olivine: The refractive indices are a = 1.684, 7=1.720, indicating 

 a content of 25 mole percent of the Fe 2 Si0 4 component, according to 

 the determinative curve of Poldervaart (1950). This was confirmed 

 by the X-ray method of Yoder and Sahama (1957). The olivine peaks 

 on the dilfractometer chart are sharp, symmetrical, and well defined, 

 indicating olivine of uniform composition. Dodd, Van Schmus, and 

 Koffman (1967) made microprobe analyses of the olivine in Cynthiana 

 and report an essentially uniform composition of Fa 2 6. 8 - 



Pyroxene: Optical and X-ray examinations show that the 

 pyroxene is largely clinohypersthene with some hypersthene. The 

 clinohypersthene shows close-spaced polysynthetic twinning, and 



