THE TEREESTRIAL PERIDOTITES. — PICRITE. 149 



and have the cleavage of hornbleude, garnet, olivine altered to serpentine in part, biotite 

 strongly dichroic and containing little opaque needles, diallage, and iron ore* 



A similar serpentine was described by Dathe from Crossen, near Slittweida, iu 

 Saxony ; but it appears to be a somewhat more altered rock {I. c, p. 245). 



Vakiety. — Picrite. 



Austria. 



Picrite, according to Tschermak, when in a fresh or little changed state, has a dark 

 green color, and varies from a finely crystalline to a plainly crystalline character. 



That from Svhle has a blackish groundmass containing a large number of olivine 

 crystals. Microscopically the groundmass holds granular feldspar, grains of magnetite, 

 scales of black mica, and little hornblende crystals. 



The Freiberg and Giliiibelherg picrite shows a dark groundmass holding olivine 

 crystals traversed by numerous fissures filled by a serpentinous minei'al ; also blackish- 

 green grains of diallage. The groundmass is similar to that of the Siihle picrite: granu- 

 lar feldspar, biotite scales, magnetite grains, and a few hornblende crystals, with here and 

 there thin strings of serpentine. . 



The picrite from Sclionau has a blackish-green groundmass holding olivine and dark- 

 gi'een mica. The mica forms aggregations of scales. Much serpentine also occurs in the 

 rock. The groundmass consists of a granular feldsjjathic mass, grains and octahedrons 

 of magnetite, blackish-green augite' crystals, rarely some needles of apatite, also calcite 

 grains, and some serpentine. 



An altered picrite from Sohle is a dark greenish-gray rock flecked with pistacite 

 green spots. It contains altered diallage and olivine crystals, hornblende prisms, dark- 

 green mica plates, magnetite grains, and silicates like gymnite and palagouite. 



Another altered picrite from Bi/.stri/c, has a clear gray very fine-grained groundmass, 

 holding inclusions of bluish-gray to apple-green and blackish-green colors. Pseudo- 

 morphs after diallage and olivine occur, while the rock further contains magnetite and 

 fine fissures filled with calcite. 



The above picrites are stated to be eruptive in the Cretaceous. 



Sfeicrdorf, Banat. 



A blackish rock resembling basalt, and containing porphyritically enclosed olivine and 

 quartz. It is somewiiat porous, and holds calcite amygdules. The section shows that 

 tlie principal minerals are olivine, augite, and hornblende. Calcite occurs as an alteration- 

 product, and quartz as an inclusion, while an isotropic base was seen. The olivine is in 

 large, well-defined crystals, and in smaller rounded forms. It is for the most part fresh, 

 but it shows here and there along its edges and the borders of its fissures an alteration to 

 a dark brown radiated fibrous aggregate. The olivine contains inclusions of glass, augite, 

 hornblende, and picotite. The latter is in large brown isotropic sharply defined octahe- 

 drons. The augite is of a light-reddish color, and the crystals are fresh with a feeble 

 pleochroism. It contains inclusions of glass and picotite. The hornblende is of a dark 

 brown color, with strong pleochroism, and contains glass particles. The hornbleude is 



* Neues Jalir. Min., 1876, pp. 241, 245. 



