CRYSTALLOGRAPHIC NOTES ON CALCITE 



By J. E. POGUE 

 Assistant Curator, Division of INIineralogy, U. S. National Museum 



With Two Plates 



(i) Calcite from Joplin, Missouri 



Although the JopHn calcites have been very completely described 

 by Farrington/ two specimens in the U. S. National Museum present 

 features of sufficient difference and interest to warrant a brief note. 



The first of these, bearing the National Museum number 84435, 

 and represented in its true proportions in plate ijii, figure i, is com- 

 posed of the scalenohedron v (2131), modified by the positive rhom- 

 bohedron r(ioii), and the rarer scalenohedrons o- (5164) and C 

 (6178). This crystal is similar in appearance to one figured by Far- 

 rington,- but in the latter the modifying scalenohedrons are zv (3145) 

 and 11 (4153). The measurements upon which the identification of 

 the forms are based, made by the contact goniometer, are as follows : 



This type, represented by two specimens in the collection, is of a 

 honey-yellow color and about 8 cm. in length. Numerous cleavage 

 cracks intersect within the crystal and reflect the light as the crystal 

 is revolved. The faces r, a-, and C are dull ; v, bright. Three faces 

 of the scalenohedron z^, as shown in the drawing, are stippled with 



' Publ. Field Columb. Mus., Geol. Ser., vol. i (1900), pp. 232-41. 

 'Ibid., plate xxix, fig. I. 



465 



