Pyrite Mineral | Uses and Properties Pyrite With a nickname of "Fool's Gold," it is surprising that pyrite often contains significant amounts of gold Pyrite crystals: Cubic crystals of pyrite on a marlstone from Navajún, Rioja, Spain. Specimen is approximately 4 inches (9.5 centimeters) across. Image by Carles Millan and used under a Creative Commons license . What is Pyrite? Pyrite is a brass-yellow mineral with a bright metallic luster. It has a chemical composition of iron disulfide (FeS2) and is the most common sulfide mineral. It forms at high and low temperatures and occurs, usually in small quantities, in igneous , metamorphic , and sedimentary rocks worldwide. The name "pyrite" is after the Greek "pyr" meaning "fire." This name was given because pyrite can be used to create the sparks needed for starting a fire if it is struck against metal or another hard material. Pieces of pyrite have also been used as a spark-producing material in flintlock firearms.

Pyrite has a nickname that has become famous - "Fool's Gold." The mineral's gold color, metallic luster, and high specific gravity often cause it to be mistaken for gold by inexperienced prospectors. However, pyrite is often associated with gold . The two minerals often form together, and in some deposits pyrite contains enough included gold to warrant mining. Physical Properties of Pyrite Uses Ore of gold Pyrite with hematite: Pyrite with hematite from Rio Marina, Isle of Elba, Italy. Specimen is approximately 3 inches (7.6 centimeters) across. Identifying Pyrite Hand-specimens of pyrite are usually easy to identify. The mineral always has a brass-yellow color, a metallic luster and a high specific gravity. It is harder than other yellow metallic minerals, and its streak is black, usually with a tinge of green. It often occurs in well-formed crystals in the shape of cubes, octahedrons, or pyritohedrons, which often have striated faces. The only common mineral that has properties similar to pyrite is marcasite , a dimorph of pyrite with the same chemical composition but an orthorhombic crystal structure.

Marcasite does not have the same brassy yellow color of pyrite. Instead it is a pale brass color, sometimes with a slight tint of green. Marcasite is more brittle than pyrite and also has a slightly lower specific gravity at 4.8. Pyrite and gold can easily be distinguished. Gold is very soft and will bend or dent with pin pressure. Pyrite is brittle, and thin pieces will break with pin pressure. Gold leaves a yellow streak, while pyrite's streak is greenish black. Gold also has a much higher specific gravity. A little careful testing will help you avoid the "Fool's Gold" problem. Massive pyrite: Massive pyrite from Rico, Colorado. Specimen is approximately 3 inches (7.6 centimeters) across. Pyrite: Pyrite with hematite from Rio Marina, Isle of Elba, Italy. Specimen is approximately 3 inches (7.6 centimeters) across. The best way to learn about minerals is to study with a collection of small specimens that you can handle, examine, and observe their properties. Inexpensive mineral collections are available in the Geology.com Store .

Uses of Pyrite Pyrite is composed of iron and sulfur; however, the mineral does not serve as an important source of either of these elements. Iron is typically obtained from oxide ores such as hematite and magnetite . These ores occur in much larger accumulations, the iron is easier to extract and the metal is not contaminated with sulfur , which reduces its strength. Pyrite used to be an important ore for the production of sulfur and sulfuric acid. Today most sulfur is obtained as a byproduct of natural gas and crude oil processing. Some sulfur continues to be produced from pyrite as a byproduct of gold production. The most important use of pyrite is as an ore of gold. Gold and pyrite form under similar conditions and occur together in the same rocks. In some deposits small amounts of gold occur as inclusions and substitutions within pyrite. Some pyrites can contain 0.25% gold by weight or more. Although this is a tiny fraction of the ore, the value of gold is so high that the pyrite might be a worthwhile mining target.

If pyrite contains 0.25% gold and the gold price is $1500 per troy ounce, then one ton of pyrite will contain about 73 troy ounces of gold worth over $109,000. That is not a guaranteed money-maker. It depends upon how efficiently the gold can be recovered and the cost of the recovery process. Pyrite is occasionally used as a gemstone . It is fashioned into beads, cut into cabochons , faceted, and carved into shapes. This type of jewelry was popular in the United States and Europe in the mid- to late-1800s. Most of the jewelry stones were called "marcasite," but they are actually pyrite. (Marcasite would be a poor choice for jewelry because it quickly oxidizes, and the oxidation products cause damage to anything that they contact. Pyrite is not an excellent jewelry stone because it easily tarnishes.) Pyrite framboid: One of the most interesting forms of pyrite is the "framboid." These tiny spheres of euhedral pyrite crystals are often found in organic muds, coal, shale, and other types of rocks.

This is a framboid from the Waynesburg coal of northern West Virginia. It is a sphere about 15 microns in diameter that is composed of cubic crystals of pyrite about one micron on a side. Pyrite and Coal Mining Sulfur occurs in coal in three different forms: 1) organic sulfur, 2) sulfate minerals, and 3) sulfide minerals (mostly pyrite with minor amounts of marcasite). When the coal is burned, these forms of sulfur are converted into sulfur dioxide gas and contribute to air pollution and acid rain unless they are removed from the emissions. The sulfide mineral content of the coal can be reduced by heavy mineral separation, but this removal is expensive, results in a loss of coal, and cannot be done with 100% efficiency. The sulfide minerals in coal and its surrounding rocks can produce acid mine drainage. Before mining, these minerals are deep within the ground and below the water table where they are not subject to oxidation. During and after mining the level of the water table often falls, exposing the sulfides to oxidation. This oxidation produces acid mine drainage which contaminates groundwater and streams. Mining also breaks the rocks above and below the coal.

This creates more pathways for the movement of oxygenated waters and exposes more surface area to oxidation. Pyrite crystals: Pyrite, cubic crystals in schist from Chester, Vermont. Specimen is approximately 4 inches (10 centimeters) across. Pyrite and Construction Projects Aggregates used to make concrete, concrete block, and asphalt paving materials must be free of pyrite. Pyrite will oxidize when it is exposed to air and moisture. That oxidation will result in the production of acids and a volume change that will damage the concrete and reduce its strength. This damage can result in failure or maintenance problems. Pyrite should not be present in the base material, subsoil or bedrock under roads, parking lots, or buildings. Oxidation of pyrite can result in damage to pavement, foundations, and floors. In parts of the country where pyrite is commonly found, construction sites should be tested to detect the presence of pyritic materials. If pyrite is detected, the site can be rejected or the problem materials can be excavated and replaced with quality fill. Pyrite fossils: Fossil ammonite in which the shell was replaced by pyrite. External view on left and cross-sectional view on right.

External view by asterix0597 and cross-sectional view by Henry Chaplin. Both images © iStockphoto. Pyrite and Organic Material The conditions of pyrite formation in the sedimentary environment include a supply of iron, a supply of sulfur, and an oxygen-poor environment. This often occurs in association with decaying organic materials. Organic decay consumes oxygen and releases sulfur. For this reason, pyrite commonly and preferentially occurs in dark-colored organic-rich sediments such as coal and black shale . The pyrite often replaces organic materials such as plant debris and shells to create interesting fossils composed of pyrite. » Characteristics of Gold Gold is Malleable Gold is extremely ductile-meaning that it can be drawn out into wire or threadlike forms without becoming brittle and breaking. It is said that gold can be drawn out so thin that a single ounce could be made to stretch a continuous length of 35 miles. That would make the thread very thin indeed, but that is exactly what is needed in today’s electronics industry, where entire circuits are being placed in chips the size of a pinhead. Because of its high electrical conductivity, its extraordinary resistance to deterioration and its ductile qualities, gold is in great demand by the electronics industry.

So it is not uncommon to find gold being used in the circuits of many of today’s common everyday electronic devices-like TV’s and calculators, not to mention in some of the more sophisticated electronics of today’s world. Gold is also commonly used by dentists and is widely used to make jewelry. Gold’s use in the making of coins has greatly increased within the past few years. Gold has another distinctive quality, which is perhaps most important to the prospector (other than its value) and that is its weight. Gold is extremely dense, one of the heaviest of all metals. The specific gravity of gold is 19.6, meaning that it weighs 19.6 times more than an equal volume or mass of pure water. Iridium (one of the platinum group metals) is one of few metals that have a higher specific gravity than gold, being 22.6. Gold is around 8 times heavier than the quartz rock which it is commonly associated with when gold is found in hardrock form. A single cubic foot of gold will weigh approximately 1187 pounds. It is this quality of gold, having a superior weight factor over the other materials usually found along with it, that is used in most gold recovery methods.

For example, watch in the following video segment how fast gold penetrates down through the lighter materials which commonly make up a streambed: Gold is Heavy Gold is not the most valuable metal, but it is extremely valuable and probably the most sought after of all the valuable metals found on earth. At today’s market exchange value, that same cubic foot of pure gold would be worth in the neighborhood of 10 million dollars. A cubic inch of pure gold would be worth about 7 thousand dollars. So gold is valuable, very valuable indeed; and it does not take very much of it to accumulate a considerable amount of wealth. There is one other distinctive quality of gold worthy of mention. In its natural form, gold is a very rich and beautiful substance to look at. In fact, this is so true that there is a saying among experienced miners, and those individuals who handle a great deal of the yellow metal, that it is not a good idea to look at any substantial amount of raw gold for very long at any given period of time. This is because it has a tendency to bring on a condition referred to as “gold fever.” This is true! The Business of Mining “Gold Fever” affects different people in different ways.

While it might make one person want to buy the gold at almost any price, it could just as easily make another want to steal it-at any price. However, the “fever” tends to always make a person want to have the gold for him or herself, and more of it if possible, with the means of getting it depending upon the character of the individual. This condition, (gold fever) is something to take note of for anyone who is planning to get involved with mining or dealing with gold. This is nothing to laugh off, for it has been the cause of a great many deaths, failures, wars, enslavements, and loss of friendships. It has altered the course of a significant amount of history- much of it being worse for the others involved. It is true that for many, gold is the thing that dreams are made of. Therefore, gold has a tendency to strike below the social behavior in a person and bring out some of the stronger passions which lie underneath. It is well to keep this strongly in mind during the stage in which you are considering whom to take on as a partner (or as employees) in a gold mining venture of any size.

One common characteristic of a person who has been touched just mildly with a case of gold fever is that he or she tends to throw good business sense to the wind and dive in head over heels, much as a young child might do if he found a tub full of his favorite candy or ice cream. It is this very same factor that the con-man stirs up and plays off of. And if you think that there aren’t a few experienced ones in the gold mining field-think again. The majority of failures in gold mining ventures are the result of this same loss of good judgment which sometimes occurs when dealing with the valuable metal. Perhaps the most successful precaution against being struck to any harmful degree with the “fever” is in honestly taking on the viewpoint that “anything worthwhile is worth lots of time and effort.” It is the persons who intend to get rich quickly without much energy output on their part who most often fail in the business of gold mining. If, upon examining your own intentions, you discover that you are interested in getting rich quickly, without having to work for it, it is almost a certainty that you have caught at least a touch of the fever.

On the other hand, if you are interested in going out into God’s country to see if you can find some of the yellow metal as an adventure, and/or perhaps to see if it can be done as a viable business enterprise, you are probably on the right track and you are more likely to succeed. And who knows, maybe you will strike a big one; it happens! Just remember that the finding and recovering of gold is similar to any other business venture. It takes a fair amount of time and work to get consistently good at it. Take it on as such and you will have less trouble-and fewer losses. SOURCE OF GOLD When considering the source of gold on this planet alone, it is necessary to study the earth and take a look at some of its more recent geological history. Scientists believe that the earth is an extremely solid mass, which grows more and more dense towards its center. It is believed that the gold which is found on the earth’s surface and in its outer crust was once deep down inside the earth’s molten mass and was carried up to the surface by the effects of volcanic activity.

In hardrock form, gold is generally found associated with quartz in the form of veins which protrude through the general mountainous rock–referred to as “country rock” by geologists. In the early days of gold mining, it was generally believed that these quartz/gold veins were once pushed up out of the lower bowels of the earth as volcanic magma. Upon this principal, it was thought that a vein should become richer as it was followed deeper into the earth. However, this was not always the case. More recently, it has been discovered that most quartz veins were not formed during the same time period as the country rock that surrounds them, but later. The cooling of the earth’s outer crust (country rock) apparently caused many cracks and fissures from which the gasses and superheated steam could escape out of the earth’s molten interior. These water vapors also carried minerals with them through these avenues of escape, with one of the predominant minerals being silica–which forms quartz. The water vapors carried other minerals upward too, of which gold, silver, iron and platinum are just a few.

Silica has distinctive characteristics of its own, one of which is that it tends to trap heavier elements when they are passed over and through it in a dissolved form. So while the water vapors pushed the heavier minerals upward towards the earth’s surface through cracks and fissures, they often combined with silica and formed vein-like structures. Formation of mineral lodes. Generally, gold is associated with quartz. However, quartz is not always associated with gold, because there are countless quartz veins that have no gold-or at least not enough gold in evidence to make the mining of the vein profitable. Veins which contain valuable minerals are referred to as “lodes.” “Ore” has been defined as any deposit of rock from which a valuable metal or mineral can be profitably extracted. When a valuable lode is found, in order to mine it, the ore is usually blasted out of the vein and is crushed down into a very fine powder from which the gold, silver and/or other valuable minerals can be extracted by any number of chemical or mechanical procedures. This entire process is called “lode mining” or “hardrock mining”.

Millions of years passed after the rich mineral lodes were formed, during which time a large amount of weathering was caused by heat and cold, animals and vegetation, rain and wind, snow and ice, glaciers and their resulting runoffs, earthquakes, and ocean tidal changes as great as 800 feet in elevation for each tide. That was due to the moon revolving closer to the earth during an earlier period. So, after the rich veins were formed, a tremendous amount of disturbance and erosion took place which washed many of the exposed rich mineral lodes out of the mountainous rock and into the stream and river systems which flowed during that time period. The steady heavy flow of water over a streambed creates a continuous movement of the streambed materials, causing a natural sorting of the various minerals by their different sizes, shapes and weights. Gold, being extremely heavy in comparison to most of the other materials that end up in a streambed, tends to be deposited in common locations where heavier materials can become trapped because of their greater weight.

Deposits of gold and other valuable minerals which have been washed away from their original lodes and redeposited by water in streambeds are called “placer deposits” (pronounced like “plaster”–without the t). Finding and recovering placer gold deposits requires an understanding of where heavy sediments will collect while being transported by the forces of water during large flood events. Gold directly from a lode is crystalline in structure, and is usually referred to as “rough gold” because of the coarseness of its surface. Once washed from its original lode and swept away by the forces of nature, gold tends to become pounded flat and rubbed smooth. Gold directly out of a lode is crystalline in structure. Gold tends to get pounded smooth as it is being washed further from its original lode. An experienced prospector can sometimes get a pretty good idea of how far a piece of gold has traveled from its lode by the degree of roughness on its outer surface. PURITY OF NATIVE GOLD In its native state out of a lode, gold is almost never 100-percent pure, but has a percentage of other metals along with it.

These other metals contained with gold, whether of value or not, are called “impurities.” The impurities with gold most often consist of silver, copper and a little bit of iron, platinum and cadmium in differing amounts. The proportions of these other minerals change from lode to lode, which gives the gold coming from one location different colors, qualities and value from the gold extracted from another location. When someone finds gold, either in placer or lode form, it is not uncommon to have the gold tested (“assayed”) to find out what percentage of impurities are present and exactly what they are. The actual gold content in native gold just out of a lode or placer deposit changes from location to location. But a reasonably safe average (at least in California) would be to say that 80% is gold and 15% is silver and/or copper.

Gold which contains 20% or more of silver is called “electrum.” Pieces of placer gold, and those pieces which have eroded from a lode, are found in a wide variety of sizes and shapes, ranging from large pieces (“nuggets”) as great as 200 pounds in weight (very rare) to “flakes,” and smaller “grains,” and even smaller “dust,” down to pieces so microscopic in size that it would take perhaps 8 million particles combined in order to accumulate enough gold to value one dollar. The following video segment demonstrates different types and sizes of natural gold which either originated from different lodes, or traveled greater distances from the same lode down along a waterway: Types and Sizes of Natural Gold The system commonly used to classify the size-differences of gold is normally accomplished with the use of mesh screen. “Mesh” signifies the number of openings contained along a lineal inch of screen or wire cloth. For example, a screen labeled “10-mesh” would contain 10 openings per lineal inch, or 100 openings per square inch.

“Twenty-mesh” would have 20 openings per lineal inch, or 400 openings per square inch, and so on. Those pieces of gold which will pass through 10-mesh (1/16″ sized openings), yet will not pass through 20-mesh (1/32″ sized openings), are classified as “10-20 mesh.” Gold passing through 20-mesh which will not pass through 40-mesh (1/64″ sized openings) is classified as “20-40 mesh,” and so on. Gold is often classified and labeled according to its size. Various sized pieces of gold are labeled as to their different mesh sizes. “Coarse gold” or “nuggets” are agreed to be any pieces of gold which will not pass through a 10-mesh screen. Medium-sized pieces of gold, flakes and so forth, are of the 10-20 mesh range, of which it would take an average of 2,200 separate pieces (“colors”) to make up a troy ounce.

“Fine gold” is of the 20-40 mesh size, of which it would take an average of 12,000 separate colors to make a troy ounce. “Flour gold” or “dust” includes all pieces which are smaller than 40-mesh, including the microscopic-sized particles. Because gold is so malleable, as it is pounded, rubbed, and pushed along by the forces of nature, the gold will tend to hold together, while some impurities will be pounded out and washed free. So generally, pieces of gold become more pure as they are pounded and worked by the different forces of nature-especially in a streambed where it can be heavily pounded by rocks, boulders and such, along with the steady flow of water to help wash away the impurities. This pounding also has the effect of breaking the gold down into smaller pieces, from which more impurities can be washed free. And so it is generally found that smaller pieces of gold are of richer gold content than the larger pieces originating from the same source. For example, the fine and flour gold recovered out of many gold-bearing streams in the Western U.S. will be found to have a gold content greater than 90%.

Nuggets recovered out of the very same deposits can be found to have a gold content of less than 80%. At first glance, this might seem to indicate that fine gold has a greater value than the coarse gold, and this is true as far as the actual gold value is concerned. However, larger pieces of gold have “jewelry specimen value,” due to their own unique and natural characteristics. So they can bring in a greater monetary return than their actual gold value. Fine gold is usually sold to a refiner, who then melts it down and refines it into pure bullion form, to eventually be sold on the world gold market. INDICATION OF GOLD CONTENT There are two ways of labeling the gold content of raw and unprocessed gold which are commonly being used in the field today. The “fineness” or “percentage system” is used most often among miners and refiners. This system breaks down the purity into thousandths in order to label the “fineness” (purity) of the gold sample.

For example, a specimen that contains 90% gold and 10% impurities would be labeled .900 fine; 88% gold content would be labeled .880 fine; 75% gold content would be indicated as .750 fine, and so on. In this system, “.999 fine” is used to indicate pure gold. The fineness system is often used among assayers to indicate the gold content in the samples which they test. The other system sometimes used to indicate the gold content in your samples or specimens is the “carat system.” This method is most commonly used within the jewelry business, and is based upon a 24-point system with 100% gold content being 24 carats, 50% gold being 12 carats, 75% gold being 18 carats, and so on. MEASURING GOLD BY WEIGHT There are also two separate measuring systems commonly being used to weigh gold.

The most commonly used is the “troy system” which is as follows: 24 grains = 1 pennyweight 20 pennyweight = 1 troy ounce 12 troy ounces = 1 troy pound Scales having these measuring increments are usually available wherever gold mining equipment is sold. This troy system is most-commonly used by miners in the field and when gold is sold on the open market. A troy pound is equal to .3732 kilograms, whereas a standard pound (avoirdupois) is equal to .4536 kilograms. So you see that they are not the same, a standard pound weighing considerably more than a troy pound. Also, please take note that there are only 12 troy ounces to a troy pound, as opposed to the 16 ounces it takes to make up an avoirdupois pound. The result is that a troy ounce weighs slightly more than a standard ounce. The other system of measuring gold is by grams. Most triple beam balance scales measure in terms of grams instead of troy increments. So it is not uncommon to find a gram scale being used to measure gold.

In this case the conversion scale is as follows: TROY–GRAM CONVERSION TABLE 1 grain = 65 milligrams FOOL’S GOLD It is not unusual for a beginner to wonder about the difference between gold and the other materials found inside of a streambed or lode deposit. Sometimes a beginner will puzzle over shiny rocks; and quite often, iron pyrites (fool’s gold) or mica are mistaken for the real thing. In fact, this is so much the case that there is a story of an entire shipload of iron pyrites having been shipped over to England from America during the 1500’s, the yellow stuff having been mistaken for gold. So you can understand where it gets the term “fools gold.” One of the best ways to get beyond your own uncertainty of what natural gold looks and feels like is to get your hands on some of the real thing. Once you have experienced real gold, you are much less likely to make mistakes. Here is a link where you can buy a sample of natural gold . Gold is a brassy yellow metal.

Once you have seen a bit of it in its natural form a few times, you will no longer have much difficulty in distinguishing the real thing from the other materials that are commonly associated along with it. Gold seldom looks anything like rock. It usually looks like metal; gold metal. The following important video segment demonstrates what placer gold looks like in its natural form: The Look of Natural Gold If you are just starting and have not yet had the opportunity to see much gold in its natural form, there are three easy tests which will validate your discoveries one way or the other: Glitter Test: Gold does not glitter. It shines. Sometimes it is bright; sometimes it is dull; but very seldom does it glitter. The thing about fool’s gold (pyrites or mica), is that because of its crystalline structure, it tends to mostly be of glittery appearance. Take the sample and turn it in your hand in the sunlight. If it is gold, the metal will continue to shine regularly as the specimen is turned. A piece of fool’s gold will usually glitter as the different sides of its crystal-like structure reflect light differently. Hardness Test: Gold is soft metal, like lead, and will dent or bend when a small amount of force is applied to it.

Pyrites, mica and shiny rocks are generally hard and brittle. Just a little amount of pounding will shatter them. Gold almost never shatters! The following important video segment demonstrates this very important point: Gold Tests Old-timers used to put specimens in their mouths and bite down to test if they were gold. This is another way of testing the larger-sized specimens. However, keep in mind that a larger-sized piece of gold is worth a great deal and the resulting tooth marks could lessen its value. If you find a true piece of gold big enough for you to bite on, I can assure you that you will have very little doubt that it is the real thing, simply because of its rich nature and its weight. But if you are still uncertain of your find, you might try using the sharp edge if a knife and gently press in on the specimen in a place which is less visible. If it is gold, an indentation can easily be made into the metal with the blade of your knife. You will not dent its surface if it is a rock or iron pyrites. Acid Test: Nitric acid will not affect gold (other than to clean it); whereas, it will dissolve many of the other metals found within a streambed.

Nitric acid can be purchased from some drug stores or prescription counters, and can sometimes be found where gold mining equipment is sold. If you question whether your specimen is some metal other than gold, you could try immersing it in a solution of nitric acid. If your specimen is gold, it will remain rather unaffected. If it is most any other kind of metal, it will dissolve in the acid. Nitric acid will not affect iron pyrites or mica (fool’s gold), but they are brittle and neither will pass the hardness test. CAUTION: Nitric acid can be dangerous to work with, and certain precautions must be taken to prevent harm to yourself and/or your equipment when working with it. These, and mixing instructions, are covered in Chapter 7 of Gold Mining in the 21st Century . The following video segment shows the negative affect that nitric acid has upon gold. But watch what the acid will do to nearly any base metal like lead: Acid Test PLATINUM Platinum is an industrial metal, one of a family of six separate metals: platinum, palladium, iridium, osmium, rhodium, and ruthenium.

These metals are frequently naturally alloyed among each other so that they are seldom found separately. Platinum is a valuable metal, its value ranging in the same neighborhood (or higher) as that of gold. It also has a high specific gravity, sometimes even heavier than gold, depending upon how much iridium is present. Sometimes, platinum will be present in placer gold deposits, and so will become trapped in the same recovery systems which are used to recover gold. Sometimes platinum will be present in enough quantity that it can be worth a great deal of money for you to know what it looks like, so you do not discard it along with the waste materials. Platinum is usually a dull silvery-colored metal, much like steel-only different, in that it is non-magnetic and is not affected by nitric acid like steel is. Platinum does not rust. Platinum usually comes in the form of large and small flakes, just like gold, and sometimes in the form of nuggets. To help you understand what platinum looks like, the following video segment demonstrates some of the platinum that I have recovered in my own suction dredge operations: Platinum Platinum does not have as great an affinity for mercury (quick-silver) as do some other shiny metals.

However, it can be made to have affinity for mercury by the use of certain involved chemical processes, or by putting a negative electrical charge into the mercury. Russia has been the world’s number one producer of the platinum metals for the last hundred years or so. If at first you have difficulty in telling the difference between platinum and lead, remember that platinum usually takes on a dull shiny color, whereas lead does not shine at all-unless it is polished or covered with a coat of mercury. Lead (and mercury) are also easily dissolved by nitric acid, whereas platinum remains unaffected. Most other shiny, silvery-colored metals which will be found in the recovery system will be magnetic. Platinum is not. SILVER Most silver mining is done by the hardrock method of extracting ore from a lode and processing out the silver by chemical and mechanical procedures. The silver recovered out of most placer deposits is still alloyed with the gold and the black sands being taken out of the deposit. Native silver has a specific gravity of about 10 or 11, so it is heavy. It will be trapped in most gold recovery systems if present as itself in a placer deposit-which is uncommon.

Generally, silver in its native form does not look like shiny silver-like in silverware. It looks more like a silver-colored rock which is uncommonly heavy. Sometimes, native silver is so tarnished that it cannot be distinguished by color at all. Tin Tin Tin is a metal full of history Contents Introduction The symbol in the title is the alchemical symbol for tin, the sign of Jupiter. The word "tin" is cognate with the German "Zinn," describing a soft, white metal with a low melting point. Its two main uses, both past and present, have been the coating of other metals, and in alloys. The alloy with copper, bronze, is of outstanding significance. In Latin, copper or any of its alloys were called aes. In Greek, the equivalent word was calkos. The essential thing was the ruddy color, different from that of gold or the white metals. Tin itself was kassiteros in Greek, but in Latin it was plumbum candidum, "white lead." Plumbum was the generic name for soft white metals with low melting points. Lead proper was plumbum nigrum, "black lead," because of the dark streak it gave when rubbed on something.

The term stannum was mostly used for an alloy of lead and silver obtained in the winning of silver. Not until the 6th century was it applied to tin, but thereafter was commonly used in this sense. The prettiest word for tin is the Spanish estaño. It evolved from stannum by first becoming stanno (the m never was strongly pronounced in Latin, and mostly nasalized the u). Then the Goths had problems with "st" so it became estanno. Finally, the double n merged into ñ when the spelling was regularized, and we have the final form. Italian stagno suffered a similar transformation (gn = ñ). The French étain is closer to the English (and Dutch) tin. Indeed, the second syllable would be prounounced just as "tin" would be. In Russian, tin is ólovo, while in Welsh it is alcam, truly different sounds. The chemical ideas of the time considered lead, tin and anything like them as flavors of one basic substance. All you had to do was add the right spices to turn them into one another. The ores were earth, and lacked fire to make them shiny. Ores absorbed the fire and became metals.

This kind of chemistry was worthless for metallurgy, but must be kept in mind when considering history. It was not to change until around 1800, and even then the fundamental reasons (electrical forces) were not known for another century. Our very useful knowledge of chemistry is a very recent development. This article discusses the properties of tin, its uses in industry, and all the curious tin lore that could be found. Some Metallurgical History Metals are important enough in the human story to be used to characterize eras of development: Copper Age, Bronze Age, Iron Age. Nevertheless, relics are few, and our knowledge of the early exploitation of metals is almost nonexistent. In such an exigency, Science fabricates stories that seem plausible to plug the gap, and these are copied from author to author until they become a solid part of the edifice of knowledge. Some metals can be picked up off the ground in metallic form, and hammered into attractive ornaments. Such native metals are gold (Au), silver (Ag), copper (Cu), platinum (Pt) and iron (Fe). These occurrences are very rare, but once they are found, the area is combed over diligently for more. How many nuggets have you discovered in your walks?

None of these native metals are good for much more than trinkets. Native iron, which occurs (very rarely) in the earth as well as in meteorites, is very hard to work and would have to be admired as crusty lumps. In the New World, there was no metallurgy; the gold found by Cortez and Pizarro had to be laboriously collected, the copper ornaments were not coveted by the invaders, and everyone was unaware of the enormous wealth in silver that lay concealed in the black sulphate. In the Old World, all the early civilizations--in China, India, Mesopotamia and Egypt--arose without metal, as Neolithic communities that settled, herded, farmed and built in mud brick. Copper, bronze and iron then appeared in succession, each granting significant advantages in tools and weapons. None of the appearances were random, and the techniques spread by diffusion, suggesting that the developments were the product of ingenuity, not chance, and very hard-won. The story is that some gormless hunters built a campfire on copper ore, and, lo, copper ran forth. "By Orm, that's copper!" one exclaimed.

Another hammered at it, enthusing "We've got copper, copper galore!" Now, the usual campfire is not hot enough to melt copper, and building the fire on the ore would not do much good, and besides copper ore does not present itself in large areas good for campfire hearths. If it were produced, it would look like the rest of the black clinker in the ashes. It is more likely (but we do not know) that the ore was thrown onto the fire because someone wanted to see what would happen. You do not see many campers throwing stones or earth (lumps of ore would be useless) on a fire, or combing through the ashes for valuable things. Once you do start throwing crushed rocks on fires, there are many possibilities. Most of them do not produce metals. The rocks have to be very carefully selected. However, if you are in the middle of a mineralized area such as western Cornwall, many curious rocks are available, a good number of which will give you metal. Many ores (an ore is a mineral from which a metal can be profitably extracted) are sulphides, such as Cu2S, chalcocite.

When you heat such a sulphide in air, the reaction 3Cu2S + 2O2 → 2Cu2O + 2SO2 takes place, creating cuprous oxide instead of cuprous sulphide. It is best not to stand downwind. This is the process of roasting an ore to drive off the sulphur. If we did this on a goodly fire, the heat would have driven the volatiles out of the fuel (wood), leaving carbon, and then the air would have formed carbon monoxide: 2C + O2 → 2CO. Of course, in the usual fire this monoxide would burn to carbon dioxide, but here it can react with the cuprous oxide: Cu2O + CO → Cu2 + CO2. It is said to reduce the copper to the metallic state, which is done by adding electrons to it. This cannot happen unless the ore is finely enough divided for the monoxide to get to it. This process is called smelting. If the fire is hot enough (1083°C) the copper will melt and run out.

The early metallurgist, however, normally got his copper as a clinkery mass that had to be hammered, annealed and rehammered before it looked like anything. This is said to have happened in Mesopotamia and Cyprus (in the West) around 3500 BC, but the date cannot be trusted. How can you date something when you really don't know what it was? Although this looks easy, and we can understand it with our current knowledge of chemistry, in practice it was not a simple operation and required experience and technique: it was, indeed, an art. It is interesting that religion did not seem to play a very great role in creating metallurgy; only afterwards did priests see an opportunity to profit from superstitious awe. Bloody sacrifices were encouraged to prevent failures, and, of course, donations to priests would not be refused. The uselessness of religion in metallurgy seems to have been realized at an early date, and in classical times it played little role, in spite of the superstitious tendencies of the general population. In medieval times, malicious spirits were blamed for making ores barren, and for ruining the product, when the real problem was a useless theory of chemistry.

The campfire theory extends to the production of bronze. Now our worthy hunters build their fire on a mixed copper and tin ore, and out pours bronze. "By Orm, look at this stuff! It's hard and would take a good edge! We rule!" This is even less likely than the accidental discovery of copper, as was pointed out by the Hoovers. Copper and tin ores do not usually occur in the same places (they do in Cornwall, but bronze did not come from there). However, once you start throwing curious crushed rocks on fires to see what happens, you are likely to see other metals, of which lead, tin and iron are the most probable. Lead and tin will run out of any serious fire as liquids, surely making an early metallurgist's day. Iron will remain as a black, spongy clinker, since the melting point of iron is 1535°C, well above the capacities of any simple fire. In fact, when fires are blown by bellows (an early invention) too vigorous blowing would melt the iron, and it would absorb impurities like carbon, and so would be ruined. Iron is a special case, and its technique is complex.

Bronze weapons are said to have been found in Britain and dated from 1800 BC. This seems roughly correct, but I would like to know what the "bronze" is, and how the date was determined. Impure copper does not count as "bronze" in this respect. Bronze has to be made by design. If you do this with mercury or zinc ores, the metal vaporizes instead, and you do not get any nice, bright liquid metal. These metals were discovered a bit later, in classical times, when someone examined the flues of furnaces that had been fed a suitable diet, and then the corresponding ores were identified. In early times it is possible that copper, tin and lead were all known. Bronze was probably always made deliberately by the addition of tin to molten copper. This required a bellows-blown furnace that would reach white heat. The properties of bronze depend very sensitively on the amount of added tin, so "accidental" alloys would not be very useful or promising. From the beginnings of the use of metals from ores, then, the roasting and smelting processes have been used, with carbon as the reducing agent.

At first, the carbon was from the charcoal created in the fire, but later it was always a purer product made by charcoal-burning. Metallurgy took place in the woods and the hills, its secrets carefully guarded to preserve monopoly, just as in the present day. Today, all the rich ores that taught mankind metallurgy are exhausted. If we had to start over again, it could not be done, at least for several million years, to allow weathering to work its wonders, or for new fluids to deposit primary ores. Properties of Tin Tin (Sn), atomic number 50, atomic weight 118.70, is a member of column IVA of the periodic table, five elements whose outer electron configuration is s2p2. Its mates are carbon (C), silicon (Si), germanium (Ge) and lead (Pb). These elements are remarkable in that they are commonly used in the pure form. Carbon is found as graphite, charcoal and coal; silicon and germanium are semiconductors, tin is found in tinplate, and lead as pipes and sheathing of electrical cables.

Carbon is extraordiarily important as the basis of organic compounds, since it can form long covalently-bonded chains and rings. Carbon is nonmetallic, silicon and germanium intermediate, tin and lead metallic. It is useful to compare tin with the other elements in its column. Tin has the unusually low melting point of 231.85°C, and the unusually high boiling point of 2260, 2270 or 2687°C, according to different authorities. This great range makes it easy to form alloys without loss in vaporization. Its latent heat of melting is 14.32 cal/g, its specific heat 0.055 cal/g-K, and its thermal conductivity is 0.1528 cal/cm-s-K. The electrical resistivity of tin is 11.5 μΩ-cm. The coefficient of linear thermal expansion is 16 x 10 per °C. Its tensile strength is low, about 2000 psi, and its Young's modulus is 5.9-7.8 x 106 psi.

It is quite soft, Mohs 1.8 or Brinell 5.0 (1000 kg, 10 mm). Tin exists in three allotropic forms. Below 18°C, the stable form is α-tin, or grey tin, with a diamond structure (like carbon, silicon and germanium) and a density of 5.765 g/cc. The lattice constant a = 0.6942 nm, and the melting point is 230°C. It is a semiconductor with a band gap of 0.08V. It is a crumbly gray nonmetal. From 18°C to 161°C, the stable form is β-tin, or white tin, a metal of tetragonal crystal structure and a density of 7.2984. This is the normal appearance of tin. The recrystallization to α-tin is very slow unless the temperature is lowered to -40°C or so, and then may take place in days.

When this destroyed Russian organ pipes, it was thought to be the work of the "tin pest." Finally, from 161°C to the melting point, γ-tin has about the same density, but rhombic crystal form. Besides tin, only carbon (graphite and diamond), oxygen (oxygen and ozone) and phosphorus (red and white) exist in allotropic forms. When β-tin is bent, it emits a sound called "tin cry" from the shearing movement between the crystal grains. This can more often be sensed by touch as a kind of grating rather than as an actual sound. Tin is remarkably lighter than the lead it resembles, which can be surprising when it is hefted. Chemistry of Tin Tin exhibits the oxidation states +2 and +4, like lead. In the +2 state, it is basic and behaves like a metal. In the +4 state, it is amphoteric and can behave in an acidic manner in alkaline solution. The oxidation state +2 is called stannous, and the +4 state is called stannic.

Tin is soluble in dilute mineral acids, and in hot potassium hydroxide, but is not attacked by food acids and alkalies. An acid solution tends to preserve the stannous state, in which tin is a powerful reducing agent, happily furnishing two electrons to anything that wants them. An alkaline solution generally results in hydrolysis, and the formation of gelatinous hydrated oxides, such as Sn(OH)4, which can serve as a mordant, like the aluminium hydroxides. The chlorides are important compounds. Stannous chloride, SnCl2, is a reducing agent. Its hydrate, SnCl2·H2O, called "tin salt," forms Sn(OH)Cl on hydrolysis. Anhydrous stannic chloride, SnCl4 is a liquid that boils at 114.1°C, recalling carbon tetrachloride, but reacting quite differently because of the amphoteric nature of tin. In water, the reaction is SnCl4 + 4H2O → 4HCl + Sn(OH)4. Stannic chloride can be made by treating tin cans with chlorine gas in the absolute absence of water.

The chlorine does not attack the iron. SnCl4·5H2O is called "butter of tin," but should not be spread on your toast. Hydrochloric acid reacts with SnCl4 to form chlorostannic acid: 2HCl + SnCl4 → H2SnCl6. This weak acid can form salts, such as (NH4)2SnCl6, called "pink salt" although it is colorless. Tin forms SnH4, stannane, after the example of methane. I can find no properties of this gas, only mention of its mere existence, but it must be curious. As an acidic element, tin forms H2SnO3, metastannic acid, and H2SnS3, thiostannic acid. A salt of thiostannic acid is important in qualitative analysis, where the reaction SnS2 + Na2S → Na2SnS3 is used to dissolve the sulphide so that tin can be separated from the other cations in its group.

Tin forms unstable nitrates, Sn(NO3)2·20H2O, with an extraordinary amount of water of crystallization, Sn(NO3)4, that decomposes at 50°C, and SnO·Sn(NO3)2, which has the temerity to explode when heated. Metallic tin can be regarded as safe, and presents no hazard of poisoning even when in contact with food. There is no vapor to worry about. Soluble tin compounds are, like all soluble compounds of heavy metals, not good snacks. Give warm soapy water or other emetic, and seek medical help. Emetics are no longer as heartily advised as before, since some poisons can cause damage going either way. This is not the case with most heavy metal poisons, however, which do not damage tissue on contact. Epsom salts will do no good, since stannous sulphate is soluble.

Mineralogy and Production of Tin The primary (that is, originally deposited) tin ore is probably stannite, a mixed sulphide, Cu2FeSnS4, "tin pyrites," which is altered by supergene enrichment to cassiterite, SnO2, the heavy, dark "tinstone" that is found in river gravels as well as in veins. Cornwall was a notable and historic source of cassiterite, but the last mine has now closed in this small but interesting mining district. Much larger amounts were found in the gravels of Malaysia, Indonesia and Thailand, which supply "stream tin" or "Straits tin" from placer deposits. Until 1946, the Straits Settlements was the name of the area that is now Malaysia, and long the chief source of tin. Bolivia and China also contain economic deposits of vein ore, and Brazil and Russia have now become major producers as the traditional sources become depleted. Southeast Asia now produces about 35%, South America 30%, China and Russia 21% of the world's tin. Tin is rare, and will be long gone by the end of the century.

The United States has little tin ore of any kind, only traces, and now imports over 85% of its needs. This figure would seem to be closer to 100%, but what is included is not specified in the statistics. In 1988, the U.S. smelted 1467 metric tons of tin from imported ores, recovered 15,249 tons as secondary tin (from tin cans), and imported 43,493 tons of metal. The average price was $4.41 per pound. The world production is about 200,000 tons annually, and an approximately equal amount is held in the U.S. strategic reserves. The main suppliers of tin to the ancient world were the Phoenicians, who carried on a trade based on their mines and smelters in the Iberian peninsula, and (traditionally) on trade with Cornwall. Greek literature mentions the Cassiterides, the "tin islands," but just what these were is not clear. Cornwall is not an island. The nearby Scilly Isles are isles, but have no tin. It was probably just a mythological source for the tin brought by the Phoenicians.

The Phoenician trade began before 1500 BC. It was probably the Phoenicians who spread tin, and with it bronze, around the Mediterranean. The lean ores currently available must be treated to remove as much of the sulphides of lead, bismuth, antimony, zinc, silver, copper and iron as possible. These sulphides cannot be eliminated easily by gravity separation in water, since they are heavy like cassiterite. There has been some success with differential flotation, however. The ore is roasted to eliminate sulphides, and leached with hydrochloric acid to dissolve the iron, copper, bismuth and zinc impurities. Then it is treated with chlorine to form chlorides of lead, bismuth, antimony and silver, which are leached out with dilute acids. The concentrated ore is then smelted in a blast furnace or a reverberatory furnace with coke or anthracite screenings to produce liquid tin. The slags generally contain a goodly amount of tin, and tin is lost in flue gases. The reverberatory furnace gives better recovery. The slag must be re-treated to recover the 10% to 25% of tin that it contains.

The tin is refined pyrolytically or electrolytically. The electrolytic process was developed by Asarco after World War I, and resembles the refining of copper. The interruption of tin supplies early in World War II led to panicked construction of a tin smelter at Texas City, Texas, the Longhorn Smelter, to use low-grade ore from Bolivia that was less subject to interception. Construction began in October 1941, and the first ingots were poured in April, 1942. The Texas site also had ample hydrochloric acid, a by-product of neighboring industries, and natural gas for fuel. I do not know the current status of this smelter, but it would have been very difficult to operate it economically after the war in the face of international competition. Bolivia has been able to rely on cocaine in the absence of ore sales, so the U.S. supports it as a Good Neighbor either way. Uses of Tin The chief use of tin, by tonnage, was for years the manufacture of tin plate. This is thin sheet steel with a coating of tin only about 2.3 μm thick. The tin adheres strongly and uniformly to the steel, protecting it from attack.

A typical tin plate alloy is 88 Sn, 7.5 Pb, 4 Cu, 0.5 Sb. Cans made of tinplate are used for food products, since the tin was not attacked by most foods in the absence of air (if it were, glass jars or lacquer would have to be used). On examining modern cans, I find that other coatings are now used in many cases, though tin is still found. If it is really tinplate, the individual crystals can be seen in the coating, and the coating is white and attractive. I found that pineapple comes in real tin cans. The tin used in tinplate is not lost, since it can be reclaimed using chlorine. However, only a part of all cans can be recycled in this way, since the collection procedures in small towns and the country are unsuitable. Tin plate is used in many ways, such as roofing and as the "tin" or telltale in a squash court. Tin plate was originally made by the "hot dip" process in which clean iron strip is passed through molten tin. Practically all tin plate is now made electrolytically, since the thickness can be better controlled.

Tin is electrolytically plated from an acid solution of SnSO4, or from an alkaline solution of a stannate. Tin does not give cathodic protection to steel, as zinc does, so it is very important that the tin coating be continuous. Any pinholes will corrode easily. Fortunately, tin gives a very complete cover. Although food acids will not attack tin in the absence of air, the presence of air may lead to attack. This can often be seen if food is left in an open can for a while. The thickness of tin plating is specified commercially by the weight of tin used per base box. A base box consists of 112 sheets, 14" x 20", or 62,720 sq. in., counting both sides. One pound of tin per base box corresponds to a thickness 0f 59 μin. The usual tin plate is 1.0-2.5 lb. tin per base box. Iron cannot be coated with lead by hot-dipping, since lead does not wet iron.

A good coating does result, however, if some metal is added that wets both iron and lead, such as tin, or if the steel is given a thin coat of copper. This is also the reason why solder must contain tin, in addition to its lowering of the melting point. Terne plate is a covering of tin and lead alloy, 75 Pb and 25 Sn a typical composition. The metal covered is usually heavy-gauge steel, not the thin strip used for tinplate. Lead gives good resistance against sulphuric acid. Tin plate can easily be given a coating of lead by hot dipping. A tinsmith is a worker in tinplate, who cuts, embosses and forms the metal, and solders seams in it. He may also repair leaks in tinplate items by soldering, or by applying a patch with solder. Excellent such work was done in colonial Mexico, together with silver work. We also have the tinker, which may be related, but the Oxford Concise says etym. dub., unfortunately. A tinker makes small repairs, which may include patching and soldering, which is called tinkering.

The name has become attached to the Irish travellers, of whom many are itinerant tinkers. The word is recorded from the 13th century (early for English), and has no cognate in Dutch or German. The Romans often dipped copper dishes into molten tin to give a better taste to the drinks taken with the tinned items. Anyone who has drunk a Moscow Mule, vodka and ginger beer, in a copper mug, will see the point. The metallic taste of copper is not always desired. Copper also reacts with the fillings in your teeth, which are higher on the electrochemical scale. Molten tin has been used to cast window glass, in the Pilkington float glass process. The glass is poured out on the hot tin, which gives it a smooth surface. Tin is heavier than glass, has a high boiling point, low vapor pressure, and does not react with the constituents of glass. At the beginning of World War II, tin was not only widely used in tinplate, but as tinfoil and tin collapsible tubes as well. The metal in this latter use could be an alloy, but it would be mainly tin.

A common tinfoil alloy was 92 Sn, 8 Zn. Cigarettes, sweets and chewing gum came wrapped in tinfoil, while toothpaste was supplied in tin tubes. These were actually very good and attractive containers. When the tin supply was threatened, these uses appeared nonessential, and a search was mounted for substitutes. I cannot find the composition of the substitute alloy used for toothpaste tubes, but it could well be a lead alloy, since the toothpaste would keep the lead in an insoluble form. Aluminum foil has replaced tinfoil generally. It was almost as satisfactory, although not as pleasantly soft as tinfoil, but could be rolled out as thinly. Metal toothpaste tubes were replaced by plastic (probably in a lead scare), and they really do not do as well, refusing to stay compressed. The old metal tubes rolled up nicely. One encyclopedia says that tin is used in toothpaste. Probably the same way glass is used in jam. The use of tin that was essential to the war effort was its use in alloys. It is in this use that there are few alternatives to tin.

A large amount of tin is used in solders, of which it is the principal ingredient, typically 60 Sn 40 Pb. The phrase "to tin a soldering iron" means to flux it, apply solder, and wipe until it is evenly coated. For more information on solders, see Lead . Pewter is an alloy ranging from pure tin to 74 Sn, 20 Pb, 3 Cu, 3 Sb. Two popular alloys have 6 Sb, 2 Cu and 4 Sb, 2 Cu, with the rest tin, or tin and lead. Pure tin is rather too soft, and the alloy hardens it a little. It is an easily workable metal for pots, platters and plates, an inexpensive substitute for silver. At today's prices for tin, it is not much less expensive than silver, however. Another important use is in bearing metals, for which the same article should be consulted. However, the principal alloy of tin is its alloy with copper, bronze. This was one of the first alloys used by man, and the first to be made on purpose to critical specifications. We have already mentioned that it is very unlikely that bronze was discovered by accident.

The strength of a bronze increases with the tin content, while its toughness and malleability decrease. The strength is a maximum at about 30%, and rapidly decreases for more tin, but at this point the bronze is hard and brittle. There is an intermetallic compound Cu3Sn that has something to do with this. For coinage, 95 Cu, 5 Sn is a good alloy, still looking like copper, but with added strength and hardness that allow it to stand up in circulation. The alloy 95 Cu, 4 Sn, 1 Zn is also used. The U.S. large cents that were struck in 1808-1814 used a purer copper than those before and after, and they wore noticeably badly. 90 Cu, 10 Sn makes a strong, tough alloy called "gun metal" from an obvious application. With more tin than 85 Cu, 15 Sn, the bronze is called "bell metal" because its hardness makes a live, resonant bell. The Liberty Bell, cast in London, cracked when rung in Philadelphia, showing the drawbacks of high-tin bronze.

My great-grandfather leaped over the barrier and rang it again at the Centennial Exhibition in 1876, futher damaging it. 67 Cu and 33 Sn give "speculum metal," a very hard white alloy (mainly Cu3Sn) that makes an excellent mirror when polished. This is the range of useful bronze alloys, and shows the general trend of their properties. The exact proportions of Cu and Sn in any particular alloy may vary from the numbers quoted, of course. Bronze is significantly improved by small additions of phosphorus, which de-oxygenates the alloy and cleans up the grain boundaries. This is the main effect of the addition, not any addition of phosphorus to the alloy, which is deleterious. Phosphor bronze is an excellent bronze, often used for springs. The very hard intermetallic compound Cu3P is formed with higher phosphorus content, and makes a brittle bronze with only special uses. The term "bronze" is used for some alloys that contain no, or very little, tin, to show that they have superior qualities. Aluminium bronze, 90 Cu, 10 Al is an example (and a very good alloy, besides).

A typical bronze for English "copper" coins was 97 Cu, 2.5 Zn, 0.5 Sn. U.S. coins contained no tin, unless the alloy for the early half-cents and cents, imported from England, contained a little tin. English copper coins were traditionally the halfpenny and the farthing (1/4 penny). From 1684 to 1692 halfpennies and farthings were issued in tin, with the date and the legend "nummorum famulus" ("servant of the coinage") on the rim. Some had a copper plug in the middle, to retain the link with copper. This was the only use I can find of tin in coinage, since tin would not not be hard enough for circulation, and it was also costly. Not even the Straits Settlements or Malaya has issued tin coins. Incidentally, the penny was a silver coin down to 1797, when it became the familiar large copper coin, last issued in 1967. The phrase "bright as a penny" referred to the small, shiny silver penny, now only found in Maundy Money.

It certainly does not refer to a copper penny or cent, and especially not to the dingy zinc cents of today's U. S. money. Tin is also preferred for organ pipes. It is said to give a better sound than aluminium or zinc. Cymbals are made from a high-tin bronze, 80-85 Cu, 15-20 Sn, which is a bell metal and gives a bright sound. Ancient Egypt was very poor in metals, which had to be imported or scratched from a few mines in the Sinai. Copper weapons, hardened only by the impurities that happened to be in the metal, were no match for the bronze weapons coming from Mesopotamia. The Second Intermediate Period, 1759-1539 BC, may have been a time of weakness in the face of the bronze of the Hyksos, who established their capital in Avaris. Ahmose, King of Thebes and founder of the 17th dynasty finally overcame Avaris in 1530 BC, perhaps with the new bronze weapons glittering in his army.

The Egyptian histories that I have say nothing about copper or brass, in spite of its undoubted importance, though ceremonial weapons of gold and copper are pictured. These times are called "Middle Bronze Age," though what this means in terms of Egypt is not clear. Archaeologists are not very careful about their chemistry or metallurgy. It does seem to be the time that the Phoenician trade in tin rose from obscurity. Tin was the secret weapon of the time, which could make hard, sharp weapons. Homer's Trojan War was fought with bronze weapons and armor. Bronze itself finally fell before the warlike iron of the Hittites and the Celts. Iron could be hardened after the weapon was formed, and could make a weapon with a hard edge and a tough core, which would shatter a bronze sword. The Dorian Greeks were armed with steel, which overcame the bronze-wielding Mycenaeans. The properties of bronze were determined mainly by the alloy, and a hard alloy like weapons bronze could not be work-hardened by hammering, as iron could. Copper had been hardened in this way, but even so was no match for bronze or iron. Now bronze was mainly used for statuary of high quality.

References Properties of tin and its compounds are found passim in handbooks such as the Handbook of Chemistry and Physics, Lange's Handbook of Chemistry, and Kent's Mechanical Engineer's Handbook. G. Agricola, De Re Metallica (1556). H. C. Hoover and L. H. Hoover, transl. (New York: Dover, 1950). W. N. Jones, Inorganic Chemistry (Philadelphia: Blakiston, 1949), Chapter 31. J. L. Bray, Non-Ferrous Production Metallurgy (New York: John Wiley & Sons, 1947), Chapter 23. R. A. Higgins, Engineering Metallurgy, 3rd ed. (London: The English Universities Press, 1971). Composed by J. B. Calvert Created 12 November 2002 Thallium Appearance and Characteristics Harmful effects: Thallium and its compounds are highly toxic. The average oral lethal dose is estimated to range from 10 to 15 mg of thallium per kg of body weight.

Agatha Christie made use of thallium’s toxicity in her novel The Pale Horse. One symptom the victims experienced, including one of the amateur investigators, was that their hair came out in clumps. Characteristics: Thallium is a very soft, malleable, lustrous low-melting, silvery metal that tarnishes in air to the bluish-gray oxide. In appearance it resembles lead . The metal can easily be cut with a knife. It usually exists in the monovalent state, Tl+, in its compounds. In the presence of water, the poisonous thallium hydroxide (TlOH) is formed. Thallium dissolves slowly in hydrochloric acid and dilute sulfuric acid and dissolves rapidly in nitric acid. Uses of Thallium Thallium sulfate, which is odorless and colorless, was used as a rat poison and as an insecticide. This use has been discontinued in some countries, including the USA. Thallium sulfide is used in photocells because its electrical conductivity increases on exposure to infrared light. Thallium oxide is used to make glass that has a high index of refraction. Thallium is also used in gamma radiation detection equipment.

Abundance and Isotopes Abundance earth’s crust: 850 parts per billion by weight, 80 parts per billion by moles Abundance solar system: 1 part per billion by weight, 10 parts per trillion by moles Cost, pure: $48 per 100g Cost, bulk: $ per 100g Source: The main minerals containing thallium are crookesite (TlCu7Se4), hutchinsonite (TlPbAs5S9), and lorandite (TlAsS2). Thallium also occurs in manganese nodules on the ocean floor. Commercially, the metal is recovered as a by-product of sulfuric acid production as thallium is also present in pyrites (iron sulfide). Thallium can also be obtained from the smelting of lead and zinc ores. Isotopes: Thallium has 31 isotopes whose half-lives are known, with mass numbers from 179 to 210.

Naturally occurring thallium is a mixture of its two stable isotopes, 203Tl and 205Tl with natural abundances of 29.5% and 70.5% respectively. References 1. William Crookes, On the Existence of a New Element, probably of the Sulphur Group, The Chemical News, Vol. III. No. 69., March 30 1861 2. John Emsley, The Trouble with Thallium, New Scientist, Vol 79 No 1115, 10 August 1978, p392 3. H.F.V. Little, A Textbook of Inorganic Chemistry. Volume IV. , 1917, Charles Griffin & Company Limited, p165 Cite this Page For online linking, please copy and paste one of the following: <a href="">Thallium</a> or <a href="">Thallium Element Facts</a> To cite this page in an academic document, please use the following MLA compliant citation: "Thallium." Chemicool Periodic Table. Chemicool.com. 24 Jul.

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Question: Because of its appearance, what common alternative name is given to iron pyrites?
Answer: FOOL'S GOLD