No. 4.) RESEARCHES ON METEORITES— MERRILL. 11 



Several attempts were made at a determination of the chemical composition of this 

 material, but with results so discordant that the matter must l)o pended awaiting further 

 investigation. 



Tennasilm, Estland, Bussia. — This stone, which fell on the 28th of June, 1872, was described 

 by G. Baron Schilling some 10 years later.' The acquisition of a fragment weighing nearly a 

 kilogram, through Krantz, in Bonn, led mo to sacrifice enough for thin sections. An examina- 

 tion of these leads to conclusions relative to its mineral composition somewhat at variance with 

 those of Schilling and is the cause of the present note. It should, however, be stated in advance 

 that Schilling apparently made no use of thin sections, but based his mineralogical determina- 

 tions wholly upon the results of chemical analysis. 



The stone is of a pronounced chondritic type, a veined spherical chondrite (Cca) according 

 to Brezina, or a limerickite if one follows Meunier. Schilling, as a result of analyses which 

 need not be repeated here in their entirety, finds the silicate portion of the stone to consist of 

 54.45 per cent olivine; 32.27 per cent bronzite, and 13.23 per cent labradorite. Cohen ^ seems 

 to have accepted these results without question and by a further calculation gives the chemical 

 composition of the labradorite as though it had actual!}' been isolated and analyzed, while as a 

 matter of fact, as noted later, labradorite, or other feldspar, is wholly lacking, at least so far 

 as the Museum material is concerned. Meunier ^ apparently accepts this mineralogical deter- 

 mination, placing the stone in his limerickite group, the mineral composition of which is ensta- 

 tite associated with bronzite and a feldspathic mineral. My observations are based upon a 

 study of four thin sections cut from different portions of the mass mentioned. As described, 

 the stone is of a gray color, plainly chondritic, somewhat soft and friable, the chondrules falling 

 away readily from the matrix when the stone is broken. The metallic constituents are scarcely 

 evident to the unaided eye. Under the microscope the chondritic structure is very pronounced 

 (see Fig. 1, PI. V). The chondrules are in some cases of beautifully limpid, well developed 

 orthorhombic pyroxenes in a somewhat fibrous base, sometimes of the radiating cryptocrys- 

 talline forms, sometimes of polj'synthetically twinned monoclinic forms, or again, of olivine. 

 In no case have I been able to find a feldspar, even in the maskelynite condition. 



This occurrence offers an interesting illustration of the danger of calculating the mineral 

 composition from chemical analyses, and also the weakness of the quantitative classification 

 when applied to rocks of this type. 



Travis County, Tex. — This stone needs a brief reference for the reason that Wiilfing in 

 his catalogue raises the question if it does not belong to the Bluff, Fayette Coimty, fall. 



Such a suggestion is wholly unwarranted, and it is safe to say would never have been 

 made by one who had seen and compared the two stones. Indeed, if the question of identity 

 were to be raised it might well be with that of McKanney, in Collin Coimty, which it closely 

 resembles. Like the McKinney stone it is black in color, very firm and compact, and pre- 

 sents on a freshly broken surface little to suggest its meteoric nature. It might well be mis- 

 taken for a fine-grained basalt. The chondritic structure is very obscure and metallic parti- 

 cles safely identified only with a microscope or pocket lens. Abundant exudations of lawren- 

 cite, made conspicuous by globules of iron oxide, serve as a fairly safe criterion of its celestial 

 nature. 



Under the microscope the resemblance to the McKinney stone is further augmented. The 

 ground is everywhere impregnated with a black material, carbonaceous * in part, which per- 

 meates into the borders of the chondrules and cleavage and fracture lines of the enstatites, 

 and the olivines have in many cases the same greenish yellow appearance suggestive of a 

 serpentinous or chloritic alteration. The enstatites of the ground are colorless except where 

 injected with the black matter which gives the dark hue to the stone. These are interspersed 

 in a manner difficult of description, with radiating and polysomatic chondrules of both 

 olivine and pyroxenes often so altered as to break up into scaly and fibrous aggregates when 



' Arch. Naturk. Liv. Est. u. Ktirlands, vol. 9, pt. 2, 1882, pp. 95-114. 



» Mclooritenkunic, vol. I, p. .110. 



» Revision des Picires Mctforiquc, etc., pp. 393-406. 



< Roasted in a closed tube tbe powdered stone yields moisture and gives a distinct empyreumatic odor. 



