76 



BULLETIN 42, UNITED STATES NATIONAL MUSEUM. 



.> o .V ' '" '""^^"^^^ ^''^'» - to 4 and in .specific gravity from 2 to 

 -..^ob. Ihe color IS pale blue, sometimes dark, and even black from 

 impurities. In many cases it lias a clay-like appearance. 



ChrysocoUa occurs in many copper mines, but generally in small 

 amounts, especially in the upper portions that have been subjected to 

 decomposing intiuences. To illustrate the occurrence of chrysocolla 

 two specimens are shown : 



^^(l)^Botryoidal form. Cornwall Iron Mine, Lebanon Connty, Pennsylvania. 



(2) Light colored and contaiuing an excess of silica, fillins seams, and showing the 

 characteristic enamel-like appearance. Memphis Mine, oP^an District DrnMl! 

 County, New Mexico. (57259.) "I'^i, -L^ona Ana 



MALACHITE. (GREEN CARBONATE OF COPPER.) 



Composition: CUOO3+OUH3O,. Hydrated basic carbonate of copper 



ZiT'^io r^''' 'f^' ^? ''"' ''"'• ^''''''''' ^''^^ 1'^^ «^"M, carbon 

 dioxide, 10.9 per cent., and water, 8.2 per cent. 



It crystallizes in the raonoclinic system, but crystals are rare Its 

 most common occurrence is in the form of incrustations, showin-'vari 

 ous tuberose, botryoidal, and stalactitic formations on the outside" while 

 the interior is generally fibrous, and often beautifully so. The iucrus 

 tation often takes place in layers. It also occurs granular and earthy 

 from impurities. It varies in hardness from 3.5 to 4 and in specific 

 gravity from 3.7 to 4.01. It has a bright-green color, while the luster 

 vanes from adamantine in the crystals to silky in the radiated forms 

 and to dull and earthy in many cases. The massive specimens are fre- 

 quently polished and used for ornamental Durposes. but for this use 

 its softness is a great disadvantage. 



Malachite is a very important copper mineral and has yielded much 

 metal, although it is seldom found alone in large amounts, being gener- 

 ally accompanied by other copper minerals. It is frequently the result 

 of the decomposition of other minerals, and is found most abundantly 

 at and near the surfoce ; in fact, wherever there has been any copner 

 mineral exposed to decomposing influences the surrounding rocks are 

 sure to be stained with malachite, so that, while malachite is found at 

 every copper mine, its presence is not a sure indication of the presence of 

 copper m large amounts. To illustrate the occurrence of malachite three 

 specimens are shown : 



( 1 ) Characteristic coating, showing the botryoidal surface and the radiated interior 

 Copper Queen Mine, B.sbee, Cochise County, Arizona. (56064 ) 

 (40^6^'''"^ ''''''''*''^ incrustations. Eagle Mine, Loudoun County, Virginia 



(3) Massive. Yankee Mine, Graham County, Arizona. (33383.) 



AZITRITE. (BLUE CARBONATE OF COPPER.) 



Composition : 2CuC03+CuH,0,. Hydrated basic carbonate of copper 

 coutani.ng copper oxide G9.2 per cent, (copper 55.30 per cent.), carbon 

 dioxide 2o.O per cent., and water 5.2 per cent. 



