8. L. Penfield — Crystallized Bertrandite. 215 



No. 1. 



No. 2. 



Calcu 



latec 



c~d 001 a 102=27° 40' 



27° 42' 



27° 



42' 



c~e 001^031 = 60° 22' 



60° 53' 



60° 



50' 



c~e 001^031=60° 58' 



60° 50' 



60° 



50' 



c^b 001 ^ 010 = 90° 1' 





90° 





in ^ m 



59° 16' 



59° 



16' 



b~h 010^130= 



29° 30' 



30° 



22' 



The crystals are not very transparent and favorable for the 

 determination of the optical properties ; in converging polarized 

 light with the microscope, an obtuse bisectrix was seen nor- 

 mal to c, the plane of the optic axes being the brachypinacoid. 



The specific gravity was carefully taken, by just floating the 

 mineral in the Thoulet solution, and found to be 2 -598, exactly 

 the same as that found for the Mt. Antero bertrandite. The 

 material being very limited no chemical tests were made. 



2. Bertrandite from Mt. Antero, Colorado. 



In a previous communication* I described crystals from Mt. 

 Antero which had a curious hemimorphic development. The 

 crystals were composed of the three pinacoids ; but while one 

 of the basal planes was flat the other was rounded and striated 

 parallel to the a axis by oscillatory combinations of the basal 

 plane with a brachy-dome, probably 011. Figure 3 represents 



a section across one of the Mt. An- 

 3 tero crystals parallel to the macro- 



~^l pinacoid which was drawn with a 

 camera lucida and magnified 17 

 diameters. During the past summer 

 a number of bertrandite specimens were found and all of them 

 showed this peculiarity. Some of the crystals which are now 

 in the collection of Mr. C. S. Bement of Philadelphia, are 

 25 mm long, 8*™ wide and 3*™ thick. That the rounding of 

 one of the basal planes is not accidental, but is owing to a hemi- 

 morphic development of the crystals, cannot be doubted. As 

 proof of this, one of the largest crystals was tested for pyro-elec- 

 tricity by the admirable method proposed by Prof. A. Kundt.f 

 The crystal was heated in the air-bath to 100° C. and on cooling 

 was dusted with a mixture of red oxide of lead and sulphur. The 

 experiment was most satisfactory, the flat basal plane showed 

 strong positive electricity and became coated with the yellow 

 sulphur, while the rounded basal plane showed negative elec- 

 tricity and was coated with red oxide of lead. - 



Tests for pyro-electricity were also made on the Stoneham 

 crystals but they were so small that it could scarcely be deter- 



* This Journal, III, xxxvi, p. 52, 1888. 



f Annalen der Physik u. Chemie, xx, p. 592, 1883. 



Am. Jour. Sci.— Third Series, Vol. XXXVII, No. 219.— March, 1889. 

 14 



