ART. 18 MINERALS OF ITALIAN MOUNTAIN CROSS AND SHANNON 15 



grains which are possibly cleavage fragments lying on a face of the 

 (110) cleavage. The maximum extinction measured on such a gi-ain 

 was 43° and the minimum 30°. Scattered grains show, in addition 

 to the contact twinning on 100 which is not observed in crushed 

 fragments, the insertion of thinner lamellse in twinned position. 



Figs. 2-3. — 2, Diopsidb Crystal of Steep Pyramidal, Habit. Projected on (010). 3, 

 DioPSiDB Crystal Twinned on (100). Projected on (010) 



Grains showing this twinning were found to be parallel to the optic 

 axial plane or perpendicular to the optic normal, and since they give 

 symmetric extinction of approximately 22° on either side of the 

 twinning plane it is probable that the twinning is on the basal 

 pinacoid c (001). 



