82 MEMOIRS NATIONAL ACADEMY OF SCIENCES, VOL. XIII. 



As to its mineralogical compoaition, the metallic portion agrees with jewellite, and yet it is distinguished by its struc- 

 ture by reason, doubtless, of special lithogenic conditions. Instead of peridotic particles the mass is formed of laminae of 

 taenite arranged in bundles which intersect at angles corresponding to those of the octahedron; the interspaces between 

 the laminae are filled with plessite, which is distinguished by its very dark gray color, contrasting with the polished 

 steel shade of the other alloy. Frequently the plessite forms spots with fusiform or more or less circular outlines, or 

 quite irregular, with a border of taenite more or less continuous, a condition which has not been noted in any other 

 meteoric iron. Near the grains of peridote the relation of the two alloys frequently takes on another character, and 

 although the Kiowa meteorite does not present the same degree of concretionary and concentric structure as the palla- 

 sites, nevertheless the silicate grains are frequently observed to be covered with the nickel-iron. It is then the plessite 

 which is in contact with the stony mineral ; it frequently constitutes a very wide zone and its exterior outline is not 

 then an the least parallel to the profile of the peridote. At more than one point several grains of olivine are enveloped 

 with the same border of plessite, which may at the same time contain different nodules. These latter ordinarily con- 

 sist of pyrrhotine, in small quantities, and of schreibersite, which, on the contrary, is quite abundant. Sometimes this 

 phosphuret constitutes the true nodules, as much as 1 cm. in diameter; sometimes it forms a sort of covering around the 

 peridotes or around small masses of sulphur. The schreibersite is of a slightly yellowish tin-white color, very fragile, 

 insoluble in hydrochloric acid, and strongly magnetic. 



The silicate portion is formed exclusively of olivine, which affords a complete analogy with the lithosiderite of 

 Pallas. It does not form true crystals at any point, but much rounded cleavage fragments completely covered with 

 metal. It is easy to dislodge the grains under consideration, with a steel point, from the cells which contain them and 

 to take the impression of the latter with wax; it is then easy to recognize fragments originally angular which have been 

 more or less corroded by the agents to which is due the concretion of the metallic portion. 



In thin sections under the microscope the peridote presents very numerous cleavages, many of which are nearly 

 filled with a perfectly opaque material which passes insensibly into the ocherous zones with which the mineral is 

 traversed. These zones frequently present opaque inclusions in which may be seen, with a strong magnifying power, 

 the indications of octahedral forms. Huntington noted the presence of chromic iron in this, but an attentive study 

 failed to reveal either oxide of iron or magnetite. The yellowish zones and the inclusions which they contain certainly 

 proceed from a particular alteration of the olivine; there is also found in their vicinity portions limited by the cleavages, 

 and which evidently consist of a serpentine material. 



Several specimens of the Kiowa meteorite have a very exceptional character. From their structure and natural 

 cohesion they prove themselves to be formed of black opaque mineral grains cemented together by a network of oxide 

 of iron. A glance shows that they are the result of an alteration of normal specimens; the metallic skeletons have 

 become oxidized and the peridotes are greatly changed. However, it does not resemble a simple attack of the elements; 

 analysis shows that the ferruginous oxide which predominates in it is neither limonite nor goethite, but magnetite. It 

 is this which constitutes nearly the whole network between the silicate grains and the filaments liberated in the tissues 

 of the peridotes. 



Brezina's account of the characters of the meteorite is given in the Vienna Catalogue for 

 1895, 8 and is as follows: 



Brenham is a highly characteristic pallasite. Among the numerous large individuals some are free from olivine 

 and can be placed with the unit oriented octahedrites. Others are in part free from olivine and in part olivine-bearing 

 pallasites, with unit orientation of the nickel-iron. Finally a third class and pieces with intimate mixtures of siliceous 

 and iron particles having a size of grains up to 5 or 6 cm., show the iron portion not oriented as a unit. This reminds 

 one of Netschsevo, in which I observed at times an intimate mixture of metallic with the stony constituents, likewise 

 a unit orientation of the iron. Most pieces of this pallasite seem to have suffered pretty strong oxidation. The olivine 

 in the peripheral parts has become abundantly turbid and is penetrated by opaque veins. The kamacite in such places 

 is altered to an opaque limonitic substance, while the plessite in part and the troilite and schreibersite almost altogether 

 remain unchanged. A plate cut from the middle of an individual weighing 36 kg. shows on the etched surface large, 

 round olivine crystals reaching 2 cm. in diameter, now single, now more or less associated, surrounded by swathing 

 kamacite 1 to 1.5 mm. thick, the intervening fields filled by now unit oriented in the greater portion and now varying 

 oriented trias in which fine taenite-rich bands stand in equal proportion with a now purely plessitic and now half 

 hatched skeleton filling. Between the olivine and swathing kamacite, schreibersite and troilite are abundantly 

 included, often as simultaneous successors of the olivine and often lying beside one another about the same olivine 

 grain, the succession being olivine, schreibersite, troilite, swathing kamacite, and trias. Loose olivine shows plane 

 bounding faces as well as round fusion forms. The latter, though, are almost never lacking and exceed the former. 

 Among the many thousands of the olivines which have been exposed by numerous sections of Brenham I have found 

 only one which was completely bounded crystalographically and this shows weak rounding of the edges. Besides the 

 large individuals there were found distributed portions of 500 or 600 little individuals which originated from a larger 

 piece by alteration. Two such specimens weighing 3.3 and 6.3 kg. are at hand; the first cleansed by washing, the 

 latter in the unchanged altered condition. They show the manner of alteration of such masses, the single constituents 

 Buffering a higher or lower degree of oxidation. 



The meteorite is quite generally distributed. 



