324 Penfield and Sjperry — Mineralogical Notes. 



would not be without interest to the readers of the Journal. 

 Crystals from Japan, with exactly the same habit, have been 

 described and figured by G. vom Hath.* The two crystals in 

 the cabinet of Professor Brush, which are 

 each about one inch in greatest diameter, 

 are very much flattened parallel to a pris- 

 matic face and have a pyramid of the 

 second order, 1212, 1-2 as twinning plane. 

 The forms are thoseof the ordinary quartz 

 combination, m (10*0, I), r (1011, 1) and 

 0(0111, -1) and are developed as shown in 

 fig. 4. The on faces are strongly striated 

 horizontally. The crystals seem to have 

 been attached only at that part where the 

 r and z faces make a small re-entrant angle, at the lower part 

 of the twin. The crystals showed no decided pyro-electric 

 phenomena. 



6. Oligoclase Jrom JBakersvllle, JV. C, with abnormal optical 



properties.\ 



The material which forms the subject of this investigation 

 was sent to us by Mr. Norman Spang, of Etna, Pa., and later 

 another fragment from undoubtedly the same locality was sent 

 to New Haven by Mr. Geo. F. Kunz, of New York. 



The mineral is remarkable for its purity, both pieces being 

 as transparent as plate glass, the only things to mar the trans- 

 parency being little bunches or tufts of minute crystals with 

 radiated structure which are scattered sparingly and irregularly 

 through the feldspar ; these show no distinct form and cannot 

 be referred to any definite species. The feldspar cleavages are 

 well shown ; one of them, the basal (001), is very perfect and 

 easily obtained ; the second, the brachypinacoid (010), is much 

 less perfect, the mineral breaking with a conchoidal fracture 

 so that it is hard to obtain a flat cleavage surface ; there is also 

 a tendency to break with an irregular conchoidal fracture par- 

 allel to the macropinacoid (100). The angle between the two 

 cleavages, 001 and 010, was measured on two fragments which 

 were carefully selected, but the results are not very satisfactory 

 owing to the poor (010) cleavage. The best of these measure- 

 ments is 001^010=88° 2' (supplement), the second gave 88° 

 45', but the reflections were poorer. If placed in position on 

 the basal plane, the crystal would have an inclination of about 

 2° to the left. An interesting point in connection with this 

 feldspar is that there is not a trace of twinning structure to be 



* Pogg. Annalen, civ, 49. 



f An account of this feldspar was given by Mr. G-. P. Kunz, with an analysis by 

 Prof. P. W. Clarke, in the September number, p. 222. 



