Galena and Cerussite
The two chief lead ores are named galena and cerussite. The first of these, which is sulphide of lead, has a sparkling crystaline and silvery appearance. Small pieces of it were often used in the crystal detectors of early wireless sets. Cerussite, which is carbonate of lead, occurs as white or coloured crystals. The metal is extracted from the ore by smelting in a furnace.
Queer beliefs about lead
Most lead contains more or less silver, which is separated from the lead if the quantity present justifies the expense of doing so. The oldest of the several processes used is named cupellation. The lead is heated in a furnace and air is blown over it. The oxygen in the air joins forces with the lead and forms lead oxide, also called litharge. The silver refuses to combine and is left behind. The lead in the litharge can be recovered by mixing the substance with carbon and heating it, when the oxygen in it goes into partnership with the carbon as carbonic acid gas and parts company with the lead.
Galena is a common and popular mineral for rock hounds. Its characteristic cubes, distinctive cleavage and high density make it easy to identify and a favorite in high school geology labs. The structure of Galena is identical to that of halite, NaCl. The two minerals have the same crystal shapes, symmetry and cleavage. Some Galena may contain up to 1% silver in place of lead. The large volume of Galena that is processed for lead produces enough Silver as a by product to make Galena the leading ore of Silver.
To quote Allen N Wollscheidt,
“Galena, back 75 years ago, was the stuff — the crystal — of crystal radio sets. Surely you have heard of these — possibly your grand or great grandparents built radio receivers out of round Quaker Oats boxes, a few feet of copper wire, a pair of headphones and a little “cats-whisker-with crystal” gadget from the hardware store. Some worked so well, they could be heard across the room.
Galena is a natural semiconductor and so the forerunner, the enabler, of all the electronic gadgets we have today, from telephones to TVs to GPS navigating systems as well as all sorts of medical equipment — in short, modern life as we know it.”
Cerussite is a popular collection mineral. It is famous for its great sparkle, great density and amazing twinned crystals. Cerussite is a minor ore of lead. It has a very high luster due mostly to the lead content. Just as leaded crystal glass sparkles more brilliantly because of its lead content, so too does cerussite. The lead raises the index of refraction of cerussite to just over 2.07. The lead is also responsible for its increased specific gravity. Cerussite has one of the highest densities for a transparent mineral. It is over six and a half times as dense as water. Most rocks and minerals average only around three times the density of water.
Cerussite is found in the oxidation zone of lead deposits usually associated with galena. Some specimens show cerussite crusts around a galena core as the oxidation was “caught in the act” so to speak. Cerussite can make nice associations with galena and another lead mineral anglesite, a yellow colored, lead sulfate.