



Dana and Wells — New mineral, Berx 



illonite. 



27 







a, 100 



&, 010 



c, 001 







a, 100 



b, 010 



c, 001 



9, 



410 



8° 9' 



81° 51' 



90° 



V', 



112 



65° 11' 



76° 6' 



28° 55' 



h, 

 h 

 h 

 m, 



310 

 210 

 320 

 110 



10° 48' 

 15° 58' 

 20° 53' 

 29° 47' 



79° 12' 



74° 2' 

 69° 7' 

 60° 13' 



90° 

 90° 

 90° 

 90° 



V, 



s, 

 A, 



111 

 221 

 331 



49° 57' 

 37° 45' 

 33° 49' 



68° 23' 

 63° 5' 

 61° 36' 



*47° 51-^ 

 65° 39' 

 73° 13' 



k, 



230 



40° 39' 



49° 21' 



90° 



R, 



411 



16° 34' 



82° 7' 



75° 32' 



I, 



n, 



120 



130 

 140 

 150 



48° 52' 

 59" 47' 

 66* 24i' 

 70° 44-|' 



41° 8' 

 30° 13' 

 23° 354/ 

 19° 15£' 



90° 

 90° 

 90° 

 90° 





212 

 211 



421 



47° 14' 

 30° 44£' 

 21° 10' 



78° 48' 

 75° 46' 

 74° 31' 



44° 56' 

 63° 23' 



75° 46' 



P, 



160 



73° 46' 



16° 14' 



90° 



<P, 



232 



53° 29' 



59° 16^' 



51° 39' 



9, 



1-12-0 



81° 43' 



8° 17' 



90° 



i, 



231 



45° 8\ 



52° 43' 



68° 25' 



a, 



102 



64° 23' 



90° 



25° 37' 



P, 



123 



73° 17' 



70° 47' 



25° 55' 



e, 



101 



46° 12' 



90° 



43° 48' 



X, 



122 



67° 12' 



63° 40' 



36° 5' 



/, 



201 



27° 32' 



90° 



; 62° 28' 



w, 



121 



57° 9' 



51° 36' 



55° 33' 



a, 



014 



90° 



82° 11' 



7° 49' 



<7, 



132 



69° 41' 



53° 24' 



43° 37' 



ft 



013 



90° 



79° 38' 



10° 22' 



X, 



131 



63° 32' 



40° 4' 



62° 19' 



7, 

 d, 

 e, 



012 

 023 



Oil 



90° 

 90° 

 90° 



74° 39' 

 69" 54' 

 61° 14' 



15° 21' 

 20° 6' 

 28° 46' 



Q, 



y, 



142 

 141 



72° 6' 

 68° 19' 



45° 17' 

 32° 15' 



50° 9' 

 67° 21' 



f, 



032 



90° 



50° 32' 



39° 28' 



z, 



151 



71° 50' 



26° 47' 



71° 1' 



AC,. 



021 

 031 

 041 



90° 

 90° 

 90° 



42° 194/ 

 31° 16' 

 24° 29' 



*47° 40+' 

 58° 44' 

 65° 31' 



T, 

 U, 



163 

 161 



77° 51' 

 74° 26' 



43° 45' 



22° 49' 



43° 50' 

 73° 45' 



A, 

 ft 



051 



061 



90 3 

 90° 



20° 1' 

 16° 53' 



69° 59' 



73° 7' 













Twins. — The existence of contact twins with m (110) as the 

 twinning plane has already been noted. These have «a=120° 

 25', measured 120° 22 r , also 55 = 59° 35'. These twins are 

 common and lead to many interesting variations in the form. 

 A basal projection .of one twin is given in figure 5. Repeated 

 twinning- is not uncommon; in several cases a large crystal 

 mass was observed having its edge formed of highly modified 

 partial crystals in successive twinning position ; some of these 

 suggest crystals of bournonite in aspect. In a single case 

 a part of a stellate form was noted which is idealized in fig. 7. 

 It was too imperfect to allow of determining the exact method 

 of grouping, but the presence of a six-rayed star was clear. 

 These twins are remarkable among similar pseudohexagonal 

 forms because the variation from the required 60° is so small.* 



General physical characters. — The cleavages already noted 

 are : highly perfect parallel to c / less perfect and interrupted 

 parallel to a; still less distinct parallel to n (130), and faintly 

 indicated parallel to b. The fracture is very perfect con- 

 choidal, yielding lustrous surfaces suggestive of glassy quartz. 



* In the preliminary notice mention was made of an apparent penetration twin 

 with a pyramid, inclined on c nearly 60°, as twinning plane. The exact measured 

 angle cc is 61° 40', giving as the angle of the supposed twinning plane on c either 

 59° 10' or 30° 50'; as these do not correspond to any occurring pyramid, the 

 occurrence is probably accidental. 



