86 PERIDOTITE. 



Section II. — The Meteoric Pcridotites. 



Variety. — Dunite. 



Chassigni/, France. 



Tlie meteorite of Chassigny * is, according to Damour, of a pale- yellow tint. Under a 

 lens it is seen to be formed of a mnltitude of little rounded grains, with a vitreous lus- 

 tre. In these grains occur some of a deep-black color. This description is identical 

 with that which could be given of an unaltered dunite, like that from Franklin, N. C, 

 for example. 



According to Tschermak, microscoj^ically, this meteorite is composed of a pale j'ellow- 

 ish olivine, traversed by fissures, and containing l)rownish glass inclusions. Between 

 the olivine grains there are to be seen here and there three-sided cavities, filled with 

 colorless or brownish glass, from which often radiate the fissures traversing the olivines. 

 In the glass can be seen with high powers colorless grains, needles, and brown crystals. 

 Octahedrons of chromite occur irregularly scattered through the rock.f 



Vaeiety. — Saxonite. 



Iov.'a Counti/, Iowa. 



The Iowa County, Iowa, meteorite in the Harvard College Cabinet presents a fine- 

 grained groundmass, sprinkled with pyrrhotite and iron. On the polished surface it 

 shows a well-marked chondritic structure. 



Tlais meteorite was described by Prof. C. W. Glimbel, in 1875, as composed of oli- 

 vine, an augitic material, iron, troilite, chromite, reddish garnet-like inclusions, etc. He 

 holds that the rock is entirely crystalline, but fragmental in character. Tlie reader is 

 referred to the original paper for Giimbers figure and views.J 



Specimens of this meteorite were purchased for the Whitney Lithological Collection 

 of the Museum of Comparative Zoology, from Ward and Howell, Eochester, N. Y., and 

 sections made. The sections are colored gray, with patches of brownish-yellow staining 

 from the iron. The gray groundmass contains irregular detached bits of metallic iron, 

 about which the stain extends. The groundmass is composed of crystals and grains of 

 olivine, enstatite, pyrrhotite, iron, and base. The section shows the usual chondritic 

 structure, in which granules of olivine and enstatite are cemented by the base to form 

 the chondri. I can find neither in this nor in any other meteorite that I have seen any 

 evidence that they are fragmental in character, but rather evidence that the structure 

 usually observed is the result of rnfid cooling upon a liquid magma of this constitution. 

 The crystalline structure of any mass depends upon the crystalline form its minerals 

 tend to assume, under the conditions to which they were exposed during that crystalliza- 

 tion. In the crystallme forms of olivine and enstatite, coupled with the rapid cooling, 



* Comptes Rcndiis, 1S62, Iv. 591. 



t Sitz. Wien. Akad., 1S83, Ixxxviii. (1), 361, 3G2. 



i Sitz. Akad. Miuiclien, 1S75, v. 313-330. 



