HOBBS MINERALOGY OF WISCONSIN. 117 



viduals to form apparent secondary enlargements to that 

 type; usually one to two inches in diameter; Galena, Lin- 

 den Mine, Mineral Point, and Mifflin. (See plate 4, fig. 4; 

 also plate 5, fig. 1.) 



Type 5. Habit, a combination of the common rhombohe- 

 dron R (1011), with the basal pinacoid, Of* (0001), and with 

 small development of R 3 (2131). The only representative 

 specimens of this type are large twinned crystals which 

 will be fully described below. Linden Mine. (See plate 4, 

 fig. 5.) 



Type 6. Habit, prismatic from development of steep 

 rhombohedron 24R. (24.0.24.1); terminal planes e, v, and 

 subordinate fc; white and opaque; Diamond Grove. Only 

 one crystal of this type has been observed. (See plate 4, 

 fig. 6.) 



Crystallographically the most interest attaches to the 

 types 3 and 4, since the crystals of type 1 are too much 

 rounded to permit of any determination of their forms, and 

 both varieties of type 2 are very simple, 2a exhibiting only 

 the form R 3 (2131) and 2b the forms R (0112) and R (lOll). 

 Although the crystals of types 3 and 4 are markedly dif- 

 ferent in their habits, between which no transitional forms 

 have been observed, they are identical in their modifica- 

 tion. The crystals of the latter type being less corroded, 

 are best suited to measurement, but even on the best of 

 these crystals the rounding of some of the faces renders 

 very accurate measurements impossible. They are also 

 too large for convenience of measuring with the reflecting 

 goniometer. The following forms have been determined, 

 those marked with an asterisk being so far as I know new 

 to the species. They are not included in the lists of forms 

 compiled by Irby, 1 Goldschmidt, 2 and Dana. 3 



1 Irby, On the crystallography of calcite. Inaug. Diss. Gottingen, 1878. 



2 Goldschmidt, Index der Krystallformen, I. Berlin, 1886. 



3 Dana, E. S., System of Mineralogy, 6thEkU..Sejy. York, 1892. 





