THE TERRESTRIAL I'KIMDOTITES. — LHERZOLITP:. 141 



Tddiiihotjs, lliulcii. 



5000, TliG specimen from this localiiy in the coHection is a blackish-fp-een compact 

 cue, containing a few enstatite and diallage crystals. It weathers to an eartliy rusty- 

 brown, showing' the network method of decomposition frequently observed in the perido- 

 tites. This with the sections was purchased from Voii't and llochttesanir, Gbttin<'en. 



One section has a greenisli groundmass liokWng crystals and grains of enstatite, dial- 

 lage, olivine, and picotite. The enstatite is in part clear and unaltered, holding picotite 

 grains, and in part it has suffered a greenish and yellowish serpentinous alteration. The 

 same can be stated of the diallage. Both are in rounded crystals and irregular ma.sses, 

 and show the usual cleavage lines. 



The olivine when unchanged is in clear grains, the remnants of the original larger 

 crystals and grains. That a series of these grains now separated by the serpentine bands 

 once formed the same crystalline mass, is shown conclusively by their possessing the same 

 optical orientation. The major portion of the oi'iginal olivine has been changed to ser- 

 pentine, the structure showing tlie successive stages of alteration. The serpentine formed 

 first along the fissures has a dividing line indicating the fissure, and on both sides the ser- 

 pentine fibres stand at right angles to that line. The color of this serpentine is generally 

 a light yellowish-green. The interior portion occupying the interspaces left between the 

 network lines above described, is occupied by serpentine of a different shade of green, 

 sometimes lighter, sometimes darker. This serpentine, which replaces the olivine grains 

 before described, shows not only by its color, but also by its structure, both in connnou 

 and in polarized light, that it possesses a distinct organization from that of the network, 

 and is distinctively a later product. The serpentine forms the chief portion of the 

 groundmass and is feebly dichroic. Wliile it is usually of some shade of yellowish-green 

 to pale-green, in some cases, especially about the feri'uginous products, it is of a bluish- 

 green color, doubtless owing to the ferrous oxide. Some secondary actinolite and talc 

 e.vist associated with the pyroxene minerals. The picotite is in coffee-brown and pale- 

 sreenish irregular grains scattered throughout the section in the different minerals. Tlie 

 larger grains along their fissures and edges are altered to a black ferruginous product, 

 probably chromite. This alteration sometimes extends nearly, and sometimes quite, 

 through the entire picotite grain. Considerable secondary iron ore exists, ^yhich is either 

 chromite or magnetite. 



Another section has a yellowish-green groundmass containing grains of enstatite, 

 diallage, and picotite, and traversed by veins of talc. Tlie groundmass is a network of 

 serpentine of a pale yellowish-green color, surrounding portions of a deeper green repre- 

 senting the unfissured parts of the olivine, while the meshes follow the fissures. The 

 enstatite and diallage are in places only slightly altered ; but for the most part they are 

 traversed by threads of the serpentine web, and possess a fibrous alteration-structure 

 showing a more or less aggregate polarization ; yet in the majority of cases they retain 

 their relative extinction. This serpentine is very beautiful in polarized light. Tlie pico- 

 tite is in irregular fissured grains, sometimes opaque, but more commonly with dark 

 brown to black edges, and with a light brown to dark reddish-brown interior. ^luch 

 ferruginous material in grains and irregular patches is distributed through the section. 



This serpentine has been referred by Eosenbusch to the Iherzolites. 



