445 



Promorphisme (Fr.) See Devitrification. 



ProtOgeniC A word applied by some authors, in contradistinction todeuterogmic, 

 to the crystalline rocks of igneous origin. 



Protopyramid ; Protoprism. See Pyramid and Prism 



Province (Fr. domaine) A petrographical province is an area characterized 

 by the constant appearance of a certain type of rocks. 



Psammitie (Naumann) Composed of small grains, as, for instance, sandstone. 



Pseudomorphous Applied to minerals possessing a crystalline form other than 

 their own, which they have obtained by the displacement or alteration of 

 the original mineral. 



Pseudospherulite (Fr. etoilement) A term applied to those belonospherites 

 (spheroidal crystalline aggregates with radial structure) which consist 

 of two or more easily distinguishable components. The granophyres often 

 contain typical pseudospherulites. The rays composing these consist 

 alternately of quartz and felspar. 



Pseudostromatism A word suggested by Bjnney (Proc. Geol. Soc., 1886, p. 65) 

 for the apparent bedding, parallel to cleavage foliation, sometimes produced 

 in crystalline rocks as a result of pressure. 



Pumieeous Having the porous nature and vesicular appearance of pumice. 



Puys (Ger. Kuppen) The name given by the French to small conical hills piled 

 up around minor volcanic vents. 



Pyramid A crystallographic form, of which each face cuts all three axes (the 

 deuteropyramids form an exception to this rule). According to their 

 parametral ratios the pyramids are classified as proto, deutero, and trito (in 

 the tetragonal and hexagonal systems) ; proto, macro, and brachy (in the 

 rhombic and triclinic) ; and proto, ortho, and clino (in the monoclinic). 



Pyroclastic A name given to fragmental igneous rocks (tuffs, &c.). 

 Pyrogenie Of igneous origin. Often used synonymously with igneous (q.v.). 

 Quadratic See Tetragonal. 



Quartz aur6o!6 (Fr.) Applied by French petrographers to the quartz-crystals 

 of certain felsophyric porphyries. These crystals are surrounded by a 

 zone of slightly turbid substance which extinguishes simultaneously with 

 the central crystal. The researches of Williams have shown that this 

 zone consists essentially of quartz, in addition to which, however, a 

 little felspar or microfelsite is present, the kaolinization of which 

 produces the slight turbidity referred to above. 



Quartzose Rich in quartz. 



Recurrence Of Phase In the consolidation of some rocks, notably those of 

 porphyritic habit, there is a recurrence of phase in the order of crys- 

 tallization ; or, in other words, allied minerals are found at two distinct 

 periods of consolidation. Those which are found first are generally large 

 and well crystallized, and constitute the "porphyritic minerals" (Ger. 

 Einsprenglinge) ; while those of the second generation are of smaller 

 size, and make up the groundmass. 



Regular The name given to one of the six systems of crystals. It is charac- 

 terized by the possession of nine planes of symmetry. The forms belong- 

 ing to this system are referred to three equal and similar axes, standing at 

 right angles to one another. Syn. Cubic, Octahedral, Tesseral, Tessular, 

 Isometric, Monometric. 



