146 



Field Columbian Museum — Geology, Vol. III. 



23 mm. (J4 in.) long in the direction of the macro-axis. All the 

 crystals are bounded by the planes m (no), b (010), z (in), and 

 z' (in), although occasionally one of the sphenoids is absent. Some 

 of the measurements taken with the reflecting goniometer on which 

 these determinations were based are as follows: 



Observed 

 (no) - 45° 35' 



, (ilo) = 8o° 20' 



(In) = 53 12' 



(1T1) = 52 38' 



Recognition of the clinopinacoid b (010) is made easy by the prom- 

 inent cleavage in that direction. In the development of the crystals 

 the prism m (no), and one of the sphenoids z 

 (in) are most prominent, although the clino- 

 pinacoid has in some of the crystals a width 

 half as great as the prismatic faces. Occasion- 

 ally, too, both of the sphenoids are found to be 

 equally developed. An average development 

 of the faces is shown in the accompanying 

 figure (Fig. 3.) 



The crystals are simple individuals with 

 the exception of two, each of which contains 

 another individual implanted upon it, but 

 not in any definite crystallographic direction. 

 The crystals are all doubly terminated, but the 

 Fig. 3. Epsomite. planes are frequently imperfect and cavities 



are numerous. When first received the crys- 

 tals were colorless and transparent, but in the Museum laboratory 

 they have deliquesced. 



LEADHILL1TE 

 SHULTZ, ARIZONA 



FIG. 1, PLATE L 



A specimen of leadhillite from Shultz, Arizona, obtained from 

 Maynard Bixby (Mus. No. M 9604), in the form of a single, 

 large, cuboidal crystal with fragments of other leadhillite crystals 

 attached, seems sufficiently unlike other occurrences of the mineral 

 to warrant description. The sides of the apparent cube of this speci- 

 men have a length of 2% centimeters. One of its surfaces is yellow- 



