Sulfides, Arsenides and Tellurides The sulfides are simple
compounds of one or more metallic elements or semimetals with
sulfur, a nonmetallic element. Typical sulfide minerals, such as
galena and sphalerite, are relatively soft, heavy, and brittle,
with a distinct metallic luster; a few, such as pyrite, give off
a sulfurous odor when struck with a hammer. The semimetallic
elements tellurium and selenium or arsenic may substitute for
one or more of the sulfur atoms. The mineral thus formed, which
is described as a telluride or an arsenide, shows physical
properties much like those of the simple sulfides. Most sulfides
are readily altered by weathering at the Earth's surface. The
water-soluble sulfide minerals may then be carried far
underground with heated groundwater, later to be redeposited at
greater depth. This process of secondary enrichment, also called
sulfide enrichment, may result in rich deposits of copper, lead,
zinc, or other metallic ores. - Chesterman, Charles W. The
Audubon Society Field Guide