Crystallogrwphic Notes by Penfield and Pirsson. 



395 



however mentioned by Schrauf, as the pyramid /i, 131, of his 

 position, and shown on a crystal from 

 Miask, Ural, in h'gure 16 of his Atlas. 

 Xis also a rare plane observed by vom 

 Rath* in crystals from Botallack, Corn- 

 wall. It is the brachypinacoid b of 

 vom Rath and Schrauf. The two rare 

 planes V and X are very prominent on 

 the Franklin crystals as seen in the 

 figure. All the faces have a line luster 

 and gave good reflections of the signal on the goniometer. 

 The planes in the zone M, s, IF", x are striated parallel to 

 their mutual intersections and the measurements in this zone 

 were therefore not so exact as the others. Some of the im- 

 portant measured and calculated angles are as follows, using the 

 following elements, d:~b;e= 049211 : 1 : 0*47970 : 





a= 82° 



54' 13" 



/3 = 91° 



51' 43" 7 =131° 32' 19 



>/ 







Measured. 



Calculated. 



Measured. 



Calculated' 



2*r, 



111 ^ 111 



= 40° 48' 



40° 46' 



m*a, 110 a 100 = 15° 25' 



15° 34' 



r * 5, 



111*010 



= 93° 22' 



93° 21' 



(is.M, 100*110 = 28° 8' 



28° 55' 



r*X, 



111 xv 021 



= 68° 24' 



68° 24' 



??z* V, 110* 112 =45° 8' 



45° 11' 



r * m' 



111*110 



= 115° 37' 



115° 38' 



z*s, 111*201=16° 5' 



16° 7' 



m * s, 



110*201 



= 27° 51' 



27° 57' 



X* if, 111*110 = 48° 46' 



48° 25' 



b * m, 



010*110 



= 32° 48' 



32° 47' 



a * W,1U *312= 9° 8' 



9° 22' 



All of the above measurements were made on one crystal 

 about 2 mm in its greatest diameter. 



The material for the analyses was dried over sulphuric acid ; 

 the boric acid was determined by Gooch's method by distilla- 

 tion with methyl alcohol. The following results were ob- 

 tained : 



Crystals. 

 1. 



Ignition = 0*76 



Si0 2 ._ 42-77 



B 2 3 5-10 



A1 2 3 16-73 



Fe 2 3 1-03 



PbO 



CnO 0-12 



ZnO 1-48 



MnO 13-69 



MgO 0-23 



CaO 18-25 



100-16 



Laminated. 



2. 



0-40 



42-47 



5-05 



16-85 



1-16 



0-09 



0-11 



1-53 



13-14 



0-26 



18-35 



99-41 



3. 

 0*41 



42-28 

 not det. 

 16-88 

 1-36 



1-57 



12-97 



0-17 



19-54 



As might be expected from this locality the mineral contains 

 a higher percentage of manganese than has ever been observed 

 before as well as some zinc. 



* Pogg. Ann., cviii, p. 243. 



