AMERICAN MUSEUM GUIDE LEAFLETS 
forms, and copper in beautifully developed crystals and crystal masses, 
presenting a great variety of shapes. All these are readily recognizable 
in luster and color from our association of them with coins, jewelry and 
other familiar things. 
SULPHIDES 
Cases 1, 2, B and 3 
The Sulphides which are here made to include the Sulpho-Salts 
are compounds of sulphur with the metallic elements. They are the 
characteristic minerals of the metallic veins from which the greater 
part of the more valuable metals are derived. In these veins, which 
were originally fissures or clefts in the rocks, vapors and fluid solutions 
highly charged with sulphur and with dissolved metals deposited their 
contents in the form of sulphides. The openings in this way ultimately 
became filled or partly filled with these minerals, which are called ores, 
together with associated unproductive minerals, such as quartz, calcite, 
and fluorite, which are known as gangue minerals. The finest and most 
characteristic specimens come from the parts of the veins which have 
not been completely filled in the process of formation and in which the 
crystallized minerals have had a chance to separate individually. This 
is illustrated by the handsome groups of stibnite crystals in long slender 
prisms (Case 1), the varied series of galena, sphalerite and chalcopyrite 
specimens (Case 2), the wide range of pyrite specimens, showing many 
complex and highly modified crystals (Case B), and the exceptionally 
fine series of proustite, pyrargyrite, tetrahedrite and enargite (Case 3). 
This division also includes many rarer minerals in notable specimens, 
such as ullmannite, sylvanite, emplectite, binnite, cosalite, bournonite, 
jordanite and stephanite. 
HALOIDS 
Cases 3 and 4 
This division of minerals includes the compounds of the metals 
with elements of the chlorine groups, the latter being known as halogen 
elements and comprising chlorine, bromine, iodine and fluorine. These 
give the chemical compounds called chlorides, bromides, iodides and 
fluorides. | 
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