THE TERRESTRIAL PERIDOTITES.— LHERZOLITE. 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 dichroism of biotite, were seen. Besides the secondary chlorite 

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

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

 is traversed by fissures.* 



Rodliaug, Gusdals See, Norimy. 



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

 enstatite plates with some grass-green diopside, and cliromite 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 grayisli-yellow ferruginous tint, and the 

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

 impellucid, and of a grayish-j-ellow 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 witli rounded edges. Portions of 

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



Basic, Hats. 



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 en.sta- 

 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, wliile the amount of clear, unaltered olivine 

 between the meslies made by the fissures grows less. Every gi-adation of alteration can be 

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

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

 ferruginous bands the former fissure lines of the olivine. In some highly altered portions 

 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 commonly 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 tliat of liebenerite. In some places it has been changed to a dirty-green 

 viriditic mass. 



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



* Neues Jahr. Min., 1870, pp. 230-232. t Nyt Mag., 1S77, xxiii. 117, 118. 



