THE TERRESTRIAL PERIDOTITES.— f.HKKZOLITE. 133 



cal relations and cleavage. Greenish, crumpled chloritic plates and fibres, forming rosette- 

 like aggregates, are associated with the garnet as an alteration-product. Also, brownish 

 plates, with the strong dichroisni of biotite, were seen. Besides the secondary chlorite 

 and biotite, magnetite and hydrous oxide of iron have been produced by the alteration of 

 the garnet. The latter mineral is next in abundance to the olivine, and in its fresh state 

 is traversed by fissures.* 



Rodhauffy Gusdals See, Norvmy. 



This peridotite is stated by Mohl to be formed of a regular mixture of olivine grains, 

 enstatite plates with some grass-green diopside, and chromite grains and octahedrons. 

 The olivine is in part changed to serpentine, but in general it is water-clear and free from 

 pores and inclusions. The grains often show a grayish-yellow ferruginous tint, and the 

 serpentinized portions are composed of short fibres, causing the fissures to appear broader, 

 impellucid, and of a grayisli-yellow color. 



The enstatite is in single scales, which are numerous and of a nacarat color. 



The very pellucid, leek-green chromdiopside is in feebly dichroic, ledge-formed pieces, 

 filled with round and pipe-formed glass pores. 



The chromite forms rounded grains or octahedrons with rounded edges. Portions of 

 these grains are of a dark liair-brown color when viewed by transmitted light. f 



Baste, Harz. 



5062. A grayish-black rock, with grayish-white spots. It shows the characteristic 

 Schiller of the enstatite (bastite), with its enclosed olivine grains. Considerable brown 

 biotite can also be seen. 



Section : dark greenish-gray, and composed of an irregular sponge-like mass of ensta- 

 tite, diallage, and feldspar, with their alteration-products, holding rounded, partially 

 altered olivines. The least altered olivines are traversed by numerous fissures, most of 

 which extend through the adjoining pyroxene. These serve as channels for the percolat- 

 ing waters, and more or less black ferruginous material exists in them. In those olivines 

 that are further changed the ferruginous bands increase, and a greenish serpentine is 

 observed bordering the sides of the fissures, while the amount of clear, unaltered olivine 

 between the meshes made by the fissures grows less. Every gradation of alteration can be 

 observed in this section, from that above mentioned to those olivines in which an entire 

 alteration has taken place, a serpentine mass remaining, which shows by its structure and 

 ferruginous bauds the former fissure lines of the olivine. In some highly altered ^^ortions 

 a few grains of olivine can be found, a mere remnant of the larger grain once there. The 

 enstatite and diallage are traversed by numerous cleavage lines and fracture planes, which 

 are bordered by a greenish serpentine. The pyroxene minerals are of a pale-yellowish 

 tinge, slightly dichroic, and in places much altered to the serpentine. The feldspar in 

 part retains the characteristic polysynthetic twinning of plagioclase, which here has the 

 same broad banding as that conmionly observed in the feldspar of gabbros. For the most 

 part it is altered to a clear or gray fibrous mass, with brilliant aggregate polarization 

 similar to that of liebenerite. In some places it has been changed to a dirty -gnnni 

 viriditic mass. 



Picotite and iron ores occur in the mass of the rock, the former mineral being fouuil 



* Neues Jahr. Min., 1870, pp. 230-232, t Nyt Mag., 1S77, xxiii. 117, US. 



