J. H. Pratt — Mineralogical Notes. 213 



b (010, i-i) x (012, %4) v (031, 34) 



c (001, O) i (021, 24) p (111, 1) 



m (110, J) 



The greater part of the crystals observed however were 

 twinned ; the twinning following the common method in 

 which the twinning plane is the unit prism m, I, 110. These 

 crystals are represented by fig. 2. As shown in the figure, the 

 crystals are extended in the direction of the twinning plane 

 and are so attached against the smooth surfaces of larger crys- 

 tal faces that the twinned pinacoids at the other end are 

 wholly wanting, the crystals being cut square off at this point 

 as in the figure. They resemble strongly the untwinned ones. 



The following table shows the identification of the forms by 

 calculated and measured angles. For obtaining the calculated 

 angles the elements of Koksharov* have been used in which, 



&:b:c= 0-609968 : 1 : 0-723002. 



m./\m, 110/\110 

 m/s P-, 1 1 /s 1 1 1 



P ^P, infill 



c /s x, 001 /s 012 

 c /v i, 001^021 



C ^ V, 001 y\ 031 



m/s,m, 110/\110(tw 

 m A p, 110/ylll " 



2. Calamine. — So far as the author has been able to dis 

 cover no calamine from any American locality has been 

 described with respect to crystal habit and it has been thought 

 that a brief description of crystals from some of the occur- 

 rences, with figures, would be of interest and not without 

 value. 



Specimens of this mineral from the majority of American 

 localities rarely show distinct isolated crystals, but rather, 

 masses of them agglomerated together upon the brachy pina- 

 coid, into rounded forms similar to prehnite and these pass into 

 indistinct botryoidal and even earthy amorphous crusts. 



In the fine suite of specimens in the Brush collection were 

 found some from Sterling Hill, ISTew Jersey, and from the 

 Harriet and Maid of Erin Mine, Clear Creek Co., Colorado, 

 which contained separate distinct crystals suitable for measure- 

 ment on the reflecting goniometer. They all show the same 

 habit being thin tabular on 5(010) and also extended so greatly 

 in the direction of the vertical axis as to form long slender, 

 delicate, needle-like forms. 



*As given in Dana's Mineralogy, sixth edition, 1892, page 286. 



Calculated. 





Measured. 





62° 45' 50" 



62 c 



1 45', 62° 45', 



62° 45|' 



35 46 



35 



46, 35 45, 



35 46| 



49 59 30 



49 



58, 49 57| 





19 52 30 



19 



49, 19 51 





55 20 



55 



19, 55 19 





65 15 



65 



9, 65 11 





54 28 30 



54 



28, 54 29, 



54 26 



43 36 30 



43 



39^ 





