Now compare a different crystal of pyrite from a mine in Spain that has produced beautiful, regular, nearly perfect cubic crystals with a chunk of galena that I recently purchased. Galena is lead sulfide, and although the pyrite (otherwise known as Fool’s Gold), has a yellowish tint and the galena more of a silvery or gray color, the luster and general appearance of the two materials are similar. Lead is atomic number 82 and is not even in the same series of elements as iron. In addition, galena is PbS, meaning it only has one sulfur atom per atom of lead! Mysteries like this are a good way to keep the flame of our curiosity burning (Fig. 2).

Figure 3 shows a spectacular specimen of pure copper metal from the A.E. Seaman Mineral Museum in Houghton, Mich. The copper grew directly in a pattern that reveals evidence of the cubic crystal structure in a different way. Nucleating crystals of copper, precipitating from copper-rich water solutions, attached themselves to the earlier-formed crystals at angles defined by copper’s face-centered-cubic structure. 

The museum, in addition to its wonderful and extensive displays of minerals, also has exhibits that educate visitors about the history of the copper mining industry in Michigan. It turns out that this metallic copper, most of which was extracted during the “Copper Rush,” was a key factor in the electrification of America at the end of the 19th century. Michigan copper allowed electrification of the 1893 Columbian Exposition (Chicago World’s Fair).