|Asia||Hongda Manganese Mine, Qugou Village, Shanxi Province, China||2 ¾" x 2 ½" x 1 ½"|
Perhaps you would have expected a specimen of silver to be shiny, like a new dime. This certainly does not look that way, but it really is silver. Silver does not react with oxygen or water, so it does not rust, like iron. But it does react with sulfur, and there is a tiny amount of H2S (hydrogen sulfide gas) in the air. Over time silver tarnishes by reaction with this. The tarnish is often black, but may be brownish gray or dark yellow. This is what has happened to this specimen.
Silver is a native element. That means that it occurs in nature as a pure element, not chemically combined with any other. For example, quartz is SiO2, two elements and calcite, CaCO3, has three. There are only around 20 chemical elements that occur uncombined with any other in the earth's crust. Some of those are so rare as to have been found in small amounts in only one or two localities.
You may have some sterling silver jewelry. It is not pure silver. The hardness of pure silver is between 2 and 3 - too soft to be used in jewelry. Sterling silver is an alloy of 92.5 percent silver with another metal, usually copper. Alloys are mixtures of two or more metals (or a metal and a nonmetal), and alloys are made in order to impart desired properties to the resulting product. For example, iron alloyed with carbon produces steel, which is stronger than iron. And silver, alloyed with a little copper, is hard enough to use in jewelry without wearing away in a short time.