Rogers. | Minerals of the Galena-Joplin District. 485 
Types 16. by oh; Ki: R*:S-,— sR; ¢-,—2R; (D:, —41R) 
—??; —??. 
Medium-sized crystals of amber color from Aurora ar: 
designated as this type. The dominant form is the unit 
prism b-. Two undetermined scalenohedrons occur, one 
modifying the intersection edge of K: and b-, and the other 
beveling the polar edges of g. These same scalenohedrons 
occur on crystals of the other types from the same locality. 
Figure 54 represents a crystal of this type. 
Tyrer 17. b, oR; S-, —ER; a, ~p2; 7-, —-R; ??. 
Small, colorless crystals from the Gracie Clark mines. The 
unit prism b- is the dominant form. Thecrystals are usually 
etched with grooves which are the traces of the cleavage 
planes on the crystal faces. No good measurements were 
possible with the reflection goniometer, and they are too 
-small for the contact goniometer to be used. ‘These crystals 
are represented by figure 55. 
Type 18. t:,+4R; K:,+R*®; ¢9.,—2R; S-,—3R; m.-,+4R. 
Large, amber-colored crystals from Granby, illustrated in 
figure 56. The crystals of this type are very much etched, 
though nothing definite can be made out concerning the etch- 
figures. g. is less affected than the other forms. Measure- 
ments are as follows: 
Assit, measure Reorees Calculated: 
t: At: 213843124 3 21° 40’ 20° 36’ 
t: at! 91384 ,2314 1 42 0 41 55 
[eal OB ABB LI 1 76 0 15 22 
K:,K:¥] 2131,3121 1 21 O 35 86 
S. ag. 0112,0221 1 38 0 36 52 
o- Am. 0221 ,4041 3 42, 30 41 16 
Typm 19. @.,—14R; A-,—2R; 8-,—iR; S-,—3R; 0, OR. 
Medium to small size crystals of amber color from the Mas- 
cot mine, at Granby. The forms % and A. occur only on this 
type. Their intersection edge is not well defined, the faces 
