SILICATES, TITANATES, KTC. 



437 



Hr:i/il ; from the Ural Mountains in Siberia, where they are asso- 

 eiated with topaz and quartz; from the Tyrol, iml>edded in a 

 chloritic schist; from North (Carolina, win-re they are associated 

 with the green spodumene, hidden! tr. 



Aquamarine, the clear blue-green variety, is more common and 

 ! valuable than the emerald. A pink or lilac-colored beryl, 

 morganite, found in a pegmatite of Madagascar and at Pala, 



FIG. 480. Beryl. The Simple Crystal is from Albany, Maine, the Other from 

 Middletown, Connecticut. 



California, where it is associated with spodumene of the same 

 color, tourmaline, and lepidolite, is also used as gem material. 



The various colors of beryl are caused by the replacement of 

 beryllium in part by the alkalies potassium, caesium, lithium, and 

 sodium ; the aluminium may at the same time be replaced by chro- 

 mium, which yields the green and bluish colors. 



Beryl is a common mineral of the pegmatites, where it is asso- 

 ciated with tourmaline, topaz, spodumene, corundum, micas, 

 feldspars, and garnets. In the Black Hills, South Dakota, it is 

 associated with cassiterite. As a product of metamorphosis it 

 occurs in the crystalline limestones, chloritic schists, and slates. 



In weathering the beryllium is carried away in solution to form 

 secondary minerals, while the aluminium and silica form kaolin, 



