176 BULLETIN 42, UNITED STATES NATIONAL MUSEUM 



It crystallizes in the ortboiliombic system, crystals being highly mod- 

 ifled and generally twinned. It frequently occurs in imitative forms as 

 a coating with fibrous structure, sometimes massive. It varies in hard- 

 ness from 4.5 to 5, and in specific gravity from 3.16 to 3.9. It has a 

 vitreous to pearly luster, and is generally white to colorless, although 

 occasionally tinted, and transparent to translucent. On being heated 

 gently it becomes electric. 



Calamine is an abundant and valuable source of zinc. It is frequently 

 the result of decomposition, and is generally associated with the car- 

 bonate smithsonite. To represent the occurrence of calamine, five 

 specimens are shown : 



(1) Crystals, distinct and free at one end, but joined at the other. Granby, New- 

 ton County, Missouri. (64175.) 



(2) Crystals, distinct and free at one end, but joined at the other, pure white. 

 Sterling Hill Mine, Franliliu, Sussex County, New Jersey. (65308.) 



(3) Crystals, complicated nuissof united, pure white. Sterling Hill Mine, Frank- 

 lin, Sussex County, New Jersey. (65312.) 



(4) Crystals, complicated naass of united. Sterling Hill Mine, Franklin, Sussex 

 County, New Jersey. (56.386.) 



(5) Massive, stained with iron. Mossy Creek, Jefferson County, Tennessee. 

 (55811.) 



SMITHSONITE. (DRY BONE.) 



Composition: ZnC03. Carbonate of zinc, containing oxide of zinc 

 64.8 per cent, (zinc 52 per cent.), and carbonic acid 35.2 per cent.; often 

 a part of the zinc is replaced by iron or manganese. 



It crystallizes in the rhombohedral system, but crystals are very 

 rare. Its most common occurrence is in imitative shapes, as an incrus- 

 tation, or granular. Its hardness is 5, and specific gravity 4 to 4.45. It 

 has a vitreous luster, and is generally white, though sometimes tinted, 

 it is subtransparent to translucent. 



Smithsonite is a valuable source of zinc, and is generally the result 

 of decomposition ; it is frequently associated with calamine, and some- 

 times with blende and galena. To illustrate the occurrence of smith- 

 sonite four specimens are shown : 



(1) Massive. Dade County, Missouri. (64153.) 



(2) Massive, milk white, slightly impure. Bertha Zinc Mine, Pulaski County, Vir- 

 ginia. (30648.) 



(3) Massive, with botryoidal surface. Dade County, Missouri. (64201.) 



(4) Massive, with botryoidal surface, lining cavities. Dade County, Missouri. 

 (64156.) 



Zinc Ores. 



Zinc ores are divided simply into oxidized and sulphide ores. The 

 former may contain several zinc minerals, the latter is universally 

 blende. Owing to the fact that the first oxidation product of blende 

 (sulphate of zinc) is soluble, it is not usual to find both characters of 

 ores associated. Whenever blende undergoes oxidation the product is 

 generally dissolved and removed before the zinc is deposited again. 



