288 C. W. Knight — Occurrence of P seudo-Leucite. 



grains of feldspar are almost always quite clear and fresh ; the 

 lath-shaped individuals around the borders, however, generally 

 show incipient kaolinization and are in consequence cloudy 

 when examined with one nicol. The scapolite is recognized by 

 its low relief, high interference colors reaching the yellows and 

 reds of the first order, cleavage cracks crossing at right angles, 

 parallel extinction and the distinct unaxial cross of negative 

 character which is readily observed in basal sections. It 

 occurs in clear allotriomorphic individuals, generally irregularly 



Fig. 2. Photo-micrograph of pseudo-leucite ; crossed nicols ; actual field 

 2*5 mm . Near the border the lath-like orthoclase individuals lie with their 

 longer axes more or less normal to the faces (icositetrahedral) of the crystal. 

 In the central portions the small allotriomorphic orthoclases are seen. 



distributed throughout the pseudo-leucite, but sometimes also 

 gathered together in little groups *4 mm in diameter. In some 

 instances the individual scapolites reach a diameter of nearly I mm , 

 but it generally occurs in grains much smaller than this. It 

 was observed in one case to have the appearance of being 

 formed directly from nephelite ; and further, the grains of 

 scapolite sometimes occupy areas whose boundaries are distinctly 

 quadratic — a characteristic form of nephelite. It should be 

 noted here that scapolite has not been described before as 

 occurring in pseudo-leucite. 



The remainiug three minerals which are seen in the pseudo- 

 crystals are nephelite, oiotite and an acid plagioelase feldspar. 

 The first of these occurs in allotriomorphic and quadratic sec- 

 tions, showing low relief and low interference colors. Basal 



