GUIE>E TO THE MIXEUALOGIC COLLECTIONS 



85 



Witherite is mined at Fallowfield Eng. Small deposits of the 

 mineral occur near Lexington Ivy. and at Thunder bay, Lake 

 Superior. 



It is used as an adulterant of white lead and in the refining 

 of beet sugar molasses. 



Strontianite SrC0 3 



Strontianite, the carbonate of strontium, contains 29.9$ carbon 

 dioxid and 70.1$ strontia. 



Distinct orthorhombic crystals are quite rare. Eadiated, 

 spear-shaped or acicular crystalline aggregates are common; 

 also columnar, fibrous and granular masses. The luster of 

 strontianite is vitreous and the color is white, pinkish or 

 greenish. 



Strontianite is found in New York at or near Schoharie, Scho- 

 harie co., Clinton, Oneida co. and in several localities in Jeffer- 

 son county. 



It is an important source of strontium compounds used in 

 the manufacture of fireworks. 



Cerussite (white lead ore) PbCO., 

 Cerussite, the carbonate of lead, contains 16.5$ carbon dioxid 

 and 83.5$ lead oxid. It sometimes carries a little silver. 



The crystals of cerussite are orthorhombic, often of tabular 



Fig. 202 



Cerussite 



Fig. 203 



habit, flattened parallel to the a and c axes as in fig. 202; the re- 

 peated twinning of this type yields six rayed forms as shown in 

 fig. 203. Crystals of prismatic and pyramidal habil are also fre- 

 quent. Clusters of interlaced fibrous crystals pass into silky 

 aggregates and masses (pi. 28J. Granular, compact or earthy 



