(public display, Carnegie Museum of Natural History, Pittsburgh, Pennsylvania, USA)
--------------------------------------
A mineral is a naturally-occurring, solid, inorganic, crystalline substance having a fairly definite chemical composition and having fairly definite physical properties. At its simplest, a mineral is a naturally-occurring solid chemical. Currently, there are over 5500 named and described minerals - about 200 of them are common and about 20 of them are very common. Mineral classification is based on anion chemistry. Major categories of minerals are: elements, sulfides, oxides, halides, carbonates, sulfates, phosphates, and silicates.
The sulfide minerals contain one or more sulfide anions (S-2). The sulfides are usually considered together with the arsenide minerals, the sulfarsenide minerals, and the telluride minerals. Many sulfides are economically significant, as they occur commonly in ores. The metals that combine with S-2 are mainly Fe, Cu, Ni, Ag, etc. Most sulfides have a metallic luster, are moderately soft, and are noticeably heavy for their size. These minerals will not form in the presence of free oxygen. Under an oxygen-rich atmosphere, sulfide minerals tend to chemically weather to various oxide and hydroxide minerals.
Galena is a lead sulfide mineral (PbS). It has a metallic luster, silvery-gray color, cubic crystals, cubic cleavage, is moderately soft, and has a very high specific gravity (it's very heavy for its size).
Galena is the most important lead ore mineral. It's principally found in hydrothermal vein systems and in Mississippi Valley-type deposits. Silver (Ag) can fall into the lead position as an impurity, sometimes in relatively high proportions. This results in argentiferous galena, (Pb,Ag)S.
Historically, lead from galena has been used as a gasoline additive, a paint ingredient, and for making bullets. Lead is also used to make various metal products, batteries, and radiation shielding.
This sample is from an old silver mining district in the Attica region of Greece and has silver impurities, making it argentiferous galena. Mining in the area started over 5,000 years ago. The silver was principally used by ancient Greeks to make coins. Sulfide mineralization is hosted in Mesozoic limestone.
--------------------------------------
From exhibit signage:
An ore sample from the silver mines of Laurium. Silver was recovered from galena (PbS) which occurred with sphalerite (ZnS) as grains and veins in limestone matrix.
The Silver Mines of Laurium, Greece
For one brief moment in history, the development of Western civilization hung upon a few small, wooden ships and the silver mines that made them possible.
Silver from the ancient mines of Laurium (Laurion) was a strong enticement for the Persian Empire to conquer Greece. Though at first, the Persians were defeated, the Athenian statesman Themistocles convinced his fellow citizens to strengthen their defense against future attacks. They pooled their annual shares of the mines’ profits to build a fleet of new ships. Sure enough, the Persians returned with great strength in 480 B.C., and descended on Athens.
The new fleet evacuated Athens and hastened to support the Greek army’s last stand across the Isthmus of Corinth. Eight hundred Persian ships closed in upon the smaller Greek fleet of 310 ships, 200 of which were the new vessels. Amazingly, the outnumbered Greeks were victorious. The Persians retreated, burning Athens in their wake. This naval battle proved to be the most decisive of the ancient world. The following year, Greek forces destroyed the Persian rear guard, and ended the threat of Persian domination.
The wealth of Laurium, which had been used to strengthen Athens’ naval forces, was then used to rebuild Athens, ushering in the Golden Age of Greece.
--------------------------------------
Locality: unrecorded/undisclosed site in the Laurium Silver Mines, Attica, southeastern Greece
--------------------------------------
For more info., see:
en.wikipedia.org/wiki/Mines_of_Laurion
--------------------------------------
Photo gallery of galena:
www.mindat.org/gallery.php?min=1641
