It orcl — Stephmiite Crystals from A7*izpe, Mexico. 247 



position. The twinning is usually quite irregular and fre- 

 quently repeated. Figure 4 shows such a twin, the faces in 

 twin position being indicated by a prime ( ' ) mark. At the 



• Normal position 



o Twin position 



extreme right hand of the figure the faces were taken as in 

 normal position ; then came a series of small faces, a', «', m', V 

 and d' in twin position. Next followed a series of X faces in 



