116 BULLETIN OF THE UNIVERSITY OF WISCONSIN. 



Type 2a. Habit, scalenohedron R 3 (2131) quite alone; 

 color, light wine yellow; translucent to transparent; crys- 

 tals almost always formed about a nucleal crystal of 

 type 1; uniformly from three to six inches long; faces 

 covered by Aetzhiigel due to much corrosion by solvents. 

 Mineral Point. (See plate 4, fig. 2a.) 



Type #&. Habit, fiat rhombohedron JR (0112) either 

 quite alone or with small face of R (1011); color like 

 type 2a; translucent to transparent; faces quite free from 

 etching phenomena ; crystals from three to five inches broad ; 

 found generally in geodes which have a diameter of a foot or 

 less. (These crystals were probably formed by the same 

 solutions as those of type 2a, the difference in habit being 

 explained by local conditions.) Mineral Point. (See plate 

 4, fig. 2b.) 



Type 3. " Dog tooth spar. " Habit, common scalenohe- 

 dron R 3 (2131) with moderate truncation by the fundamental 

 rhombohedron R (1011) and much modified; color, grayish 

 white; poorly translucent; faces marked by Aetzfiguren and 

 Aetzkandle but generally without Aetzhrtgel, hence less cor- 

 roded than crystals of type 2a; usually has a core of type 

 2a within which is a core of type 1; two sizes of crystals, 

 about two inches and four to seven inches long respec- 

 tively. Linden Mine and Galena. (See plate 4, fig. 3.) 



Type 4. " Nail head spar. " Habit, fundamental rhom- 

 bohedron R (1011) moderately beveled by the common scal- 

 enohedron R 3 (2131) and much modified, the forms being 

 the same as on crystals of type 3; color, like type 3 but 

 considerably more translucent, being in this respect inter- 

 mediate between types 2a and 3; less marked by etchings 

 than type 3; occurs either alone or as parallel growths on 

 surface of crystals of type 3, forming knobby projections 

 if attached to the lateral faces, and scepter calcite resem- 

 bling "scepter quartz" if attached to the apex of the crys- 

 tals; when large numbers of these crystals are attached to 

 the faces of crystals of type 3 they may unite as sub-indi- 



