Although it's specific gravity is almost one half that of gold and platinum and today it is considerably the least expensive of its counterparts, it is surprising that this metal at one time - many centuries ago - was considered much more valuable than gold. It was because of its extreme rarity in many ancient civilizations. This was the case for the Egyptians and Greeks, as well as others such as the Hittites, Babylonians and Sumerians. It was called "The White Gold" during these earlier Dynastic times because of its color and because it was considered, in their religious context, as being the moon metal relating to the moon god and goddess. Because of its hardness of 2.5-3 and its similar crystalline properties to gold and copper, it is in the "Gold Group" of metals classification. Silver has the highest conductivity of electricity and heat, is one of our earth's native metal elements and by its very nature is a highly chemical reactive metal. The silver that has been found in many of the ancient tombs was highly alloyed with gold and some copper to deter oxidation. Only on few occasions has silver ore ever been found and mined in its natural and pure form (called its primary form). When such finds occur they become world-renowned. The great mines of Kongsberg in Norway, Erzgebirge, Schneeberg and Annaberg in the eastern regions of Germany and the famous "Cerro de Potosi Mine" in Bolivia (that supplied the Spanish with silver to finance the building of the Spanish Armada in the mid 1500's) are examples of such primary deposits.
Because silver is not usually found in its pure form, it requires added mining techniques to separate it from the many minerals that are found with it, such as: silver chlorite, zeolite, nickel, cobalt, iron, bismuth, cassiterite (tin), lazulite and wolframite, etc.. Due to the fact that much of the silver at the times of the ancients was disguised in the surrounding rock minerals, unlike gold, it was very elusive to find and thus extremely rare and valuable. The ancient civilizations just did not have the expertise to identify and recognize the surrounding minerals (called silver's secondary form of deposits, the much more common form). In addition, it was difficult to spot due to the fact that it deeply tarnishes as it weathers. To the ancients, it just was not readily recognizable in its surrounding rock formations as gold and other metals that would stand out and be much more easily identified.
In America, in the 1800's, many boom and bust towns popped up. These were sometimes called "Chlorites" because they processed short, leaner ore deposits only to become "ghost towns." The largest silver secondary deposit in North America was found in 1903 near Cobalt, Ontario, Canada. A railroad construction worker who picked up a copper-red specimen along the rail bed discovered it. It was sent to a provincial geologist by the name of W. G. Miller. He identified it as niccolite and realized that it was sometimes historically found in association with silver. In just ten short years, 100 million dollars of silver was mined from that locale.