The aluminum content in it is leeched from the soil above. Cobalt is famous for the incredible blue color it imparts to glass and pigment. It has been found in meteorites and is used in invisible ink.
It is a brittle metal and resembles iron. Fluorite fluorspar is commonly used to create fluorescent pigment and since it is very beautiful, it is used for gem material.
It is mined all over the world. Gold is the most familiar metal to most people. It is used for jewelry, dentistry, electronics and a host of other applications. It is the most malleable metal which increases the way it can be used.
Halite [image right] sodium chloride--salt is used for seasoning food and softening water. It is also used to make certain acids, in fire extinguishers and melting ice on the road. Iron Ore is perhaps as important to civilization today as gold historically has been.
It is used in all sorts of construction from vehicles to buildings. Lead has a bad reputation for its poisoning capabilities, some of which may have been exaggerated by fear. It cannot be absorbed by the skin or breathing, but it is harmful if it touches food or drink. It was at one time used in paint, pencils and eating utensils. Lithium is used in several applications including medication for bipolar symptoms and batteries. Lithium has become very popular with the advent of electric cars.
Manganese with iron impurities can be slightly magnetic. It is essential in the steel making process, and petroglyphs were carved into it in the Southwest. Mica is the mineral responsible for putting a sparkle on many rocks. This mineral is very flexible, and large sheets of it were used as window glass in the past. Nickel is a common metal in everyday life. It has been used in currency, jewelry and eating utensils and is used in alloys as well. Potash is the old fashioned term for Potassium.
Potassium is a major component in crop fertilizer around the world. It is also used in soap manufacture. Native Americans polished it to use as a mirror, and it is occasionally used in jewelry. Its byproduct is used in ink and disinfectants. Quartz [image left] silica is the most abundant mineral on earth. It is the name for a large family of rocks including the jaspers, agates, onyxes and flints. Quartz is used in concrete, glass, scientific instruments and watches.
Most importantly today, it is used to make silicon semiconductors. Silica is used in desiccants to remove moisture from the air. It is also used in sandpaper and glass making. Rare Earth Elements lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium ytterbium and lutetium Many of these are used to create nuclear power.
Silver is one of the precious metals. It is used as currency and in jewelry making. It is also used in medicine due to its anti microbial properties. Sodium Carbonate soda ash or trona is used to control the pH of products. It is used to make glass, paper, detergents and for softening.
Sulfur [image right] is one of the only minerals to be found in its pure form in nature. It is a major ingredient in acid rain but it also is used in wine making and fruit preservation.
Tantalum is used when an alloy needs a high melting point and strength. It is used in missiles, aircraft parts and vacuums. Titanium is one of the most abundant and toughest metals on Earth.
It is used extensively in human body repair. Tungsten is a metal that is stronger than steel and a high melting temperature. It is also used to make saw blades and used in welding.
Uranium is a highly radioactive element. It is used in cancer treatments, X-rays, military weapons and fuel for the space shuttle. Gemstones are usually measured by their hardness, size, and rarity.
Unpolished gemstones simply look like ordinary rocks; cutting and polishing allows them to have brilliance and sometimes color leading to their value that can't be found in other types of stones.
Gemstones are usually classified as semiprecious and precious stones. Some semiprecious gemstones include amethyst, garnet, citrine, turquoise, and opal. Precious gemstones include diamond, emerald, ruby, and sapphire. The scientific term for rocks is petrology, and understanding them is crucial for understanding the formation and mineral makeup of the earth.
Rocks are made from minerals and can come in every size: They can be tiny pebbles or mountains big enough on which to climb or drive. Rocks do not have a special chemical or mineral makeup.
While most rocks are not cut or polished to be used as gemstones, some rocks, including lapis lazuli, are classified as gems. Minerals occur naturally within the earth's surface and are solid formations. They are defined by their shape and their crystalline makeup. They are formed when magma, which is molten rock, cools. They can also be formed by water in caverns under the sea.
Minerals are usually found between sediments or in areas that contain lava flows. There are more than 4, minerals that are formed naturally within the earth, and each one has a specific crystal structure.
Minerals belong to one of 15 different chemical groups, and these represent the compounds they contain. Minerals have different distinct classifications. Some of these are color, luster, tenacity, hardness, and fracture. Some minerals can have properties such as radioactivity or fluorescence as well. Minerals are mined for several different reasons. There may be a distinct need for the different elements that they may contain, but some are mined simply for their appearance.
The table seen here lists common ore minerals for various metals. The minerals include the native metals copper and gold, and many sulfides, oxides, and hydroxides. Minerals in these groups are generally good ore minerals because they contain relatively large amounts of the desired elements. Furthermore, processing and element extraction are usually straightforward and relatively inexpensive. That is why we mine Cu and Cu-Fe sulfides for their copper content and iron oxides for their iron content.
Silicate minerals, although common, are generally poor ore minerals and are not included in the table. For example, although aluminum is found in many common silicates, tight bonding makes producing metallic aluminum from silicates uneconomical. We obtain most aluminum from Al-hydroxides found in bauxite deposits. We discussed igneous and sedimentary minerals in previous chapters. In the following section, we focus on economic minerals that belong to other groups. Native elements have high value because they may require no processing before being used in manufacturing, as currency, or for other purposes.
The first metals ever used by humans were native minerals. Only later did humans develop refining techniques for the extraction of elements from more complex minerals. We conveniently divide native elements into metals, semimetals, and nonmetals based on their chemical and physical properties.
The table to the right includes the most common minerals of each group. Within the metal group, the principal native minerals are gold, silver, copper, and platinum. These four minerals all contain weak metallic bonds. Gold, silver, and copper have further commonality in their chemical properties because they are in the same column of the periodic table. Gold and silver form a complete solid solution; we call compositions containing both gold and silver electrum.
But, because copper atoms are smaller than gold and silver atoms, solutions are limited between copper and the precious metals. Native gold, silver, and copper may contain small amounts of other elements. For example, native copper frequently contains arsenic, antimony, bismuth, iron, or mercury. Native platinum is much rarer than gold, silver, or copper. It typically contains small amounts of other elements, especially palladium.
The native semimetals arsenic, antimony, and bismuth are also rare. Native copper, gold, silver, and platinum have atomic structures with atoms arranged in a cubic pattern Figure 9.
Iron does, too, although native iron is rare, except in meteorites, and the atomic arrangement in native iron is not quite the same as in the other metals.
Nonetheless, euhedral crystals of any of these minerals may be cubic or, as we will explain in the next chapter, octahedral. More typically, however, these minerals crystallize in less regular shapes. Native zinc, a very rare mineral, has a hexagonal atomic arrangement and so forms crystals of different shapes. The photos below Figures 9. Gold, sometimes mined as nuggets or flakes see the example in Figure 9.
Large, visible specimens, like the one seen below in Figure 9. Most gold and other precious metal ores contain very fine subhedral metal grains, often microscopic. Silver sometimes occurs in a wire-like or arborescent tree-like form Figure 9. It also easily tarnishes and so has a gray color in this photo.
Most bedrock gold and silver deposits are in quartz-rich hydrothermal veins. Besides hard-rock deposits, gold and silver are also found in placers accumulations in river, stream, or other kinds of sediments , and native silver is found in several other types of deposits.
Box below describes the Witwatersrand gold deposits, the largest gold deposits in the world. Section 9. The sample is 4 cm tall. The largest are about 2 mm across. Copper is found as branching sheets, plates, and wires, and as massive pieces.
In Figure 9. We mine native platinum primarily from ultramafic igneous rocks, but platinum is also found in placers — Figure 9. Platinum is also a secondary product of Cu- or Ni-sulfide refining. Native antimony in Figure 9. It is usually in solution with arsenic and may contain small amounts of other metals. Untarnished specimens are metallic and silvery, but antimony typically tarnishes to a gray color as seen in this photo.
Graphite, diamond, and sulfur are examples of nonmetallic native elements. Figure 3. Sulfur deposits are associated with volcanoes, often concentrated at fumaroles. Sulfur is also found in veins in some sulfide deposits and in sedimentary rocks where it is found with halite, anhydrite, gypsum, or calcite.
Most of the rest is separated from sulfides during processing to recover metals. Both graphite and diamond consist only of carbon. We discussed the nature of the two minerals in Box of Chapter 3. Graphite is common as a minor mineral in many kinds of metamorphic rocks, including marbles, schists, and gneisses.
The origin of the carbon is usually organic material in the original sediments. Graphite also occurs in some types of igneous rocks and in meteorites. Diamond only forms at very high pressures associated with the lowermost crust or mantle of Earth. We mine it from kimberlite pipes, where rapidly moving, sometimes explosive, mafic magmas have carried it up to the surface.
After formation, diamond sometimes concentrates in river and streambeds where we mine it from placer deposits. Although some diamonds are of gem quality, most are not. We call lower-quality diamonds industrial diamonds or bort if the diamonds are small and opaque. See section 9. Gold occurs in many different ore deposits. The yellow grains are gold, and the black material is uraninite.
This ore, like many Witswatersrand ores, is quite radioactive. The Witwatersrand deposits are paleoplacer deposits, meaning that they were placers when originally deposited. They occur in an area about km by 40 km. The origin of the Witwatersrand deposits is a bit of a mystery. Placers form when hard-rock deposits are eroded, and sedimentary processes concentrate ore. Yet today we know of no hard-rock gold deposits of sufficient size to account for the volume of the Witwatersrand placers.
The Witwatersrand gold prospects were discovered in , but the discovery was kept secret. It was not until that significant production began.
A booming mining industry led to the rapid growth of Johannesburg, a central town in frontier South Africa. Within a decade, Johannesburg was the largest city in the country. When miners reached a zone of pyrite in , the mining slowed because it was not known how to extract gold from sulfides at the time. Subsequently, John MacArthur, Robert Forrest and William Forrest, three Scotsmen working for the Tennant Company in Glasgow, developed a dissolution process involving cyanide that would extract gold from sulfides.
So, Johannesburg flourished once more. Most are quite rare. The table seen here lists the more important species. Pyrite iron sulfide is most common. Other relatively common sulfides include chalcopyrite copper iron sulfide , molybdenite molybdenum sulfide , sphalerite zinc sulfide , galena lead sulfide , and cinnabar mercury sulfide.
The others in the table are less abundant but are occasionally concentrated in particular deposits. Sulfide minerals such as pyrite contain one or several metallic elements and sulfur as the only nonmetallic element.
Bonding is either covalent, metallic, or a combination of both. Other very uncommon minerals grouped with the sulfides because of similar properties contain selenium the selenides , tellurium the tellurides , or bismuth the bismuthides instead of sulfur. A related group of minerals, the sulfosalts , contains the semimetals arsenic and antimony in place of some metal atoms.
Because many sulfides have similar atomic arrangements, solid solutions between them are common. The same holds true for the sulfosalts. Primary sulfide minerals consist of sulfur and reduced metals. It can also create new minerals. So, iron-bearing sulfides may turn into iron oxide magnetite or hematite , iron hydroxide limonite or goethite , or iron carbonate siderite. Galena lead sulfide may become cerussite lead carbonate. Copper sulfides may become azurite or malachite both hydrated copper carbonates.
Sulfide minerals often form in common associations. Pyrite, sphalerite, and pyrrhotite are frequently found together, as are chalcopyrite, pyrite, and bornite or pyrrhotite.
In some carbonate-hosted deposits, sphalerite and galena occur together. We can depict sulfide associations using triangular composition diagrams.
Box below presents a detailed discussion of Cu-Fe-S ore minerals and explains how we use triangular diagrams to show solid solution compositions.
Unlike other mineral groups, especially the silicates, color is sometimes a good way to identify sulfide minerals. The reason is that transition metals often control color, and the color of sulfides is often due to the metals they contain. So, color is helpful. Sulfide minerals, however, show lots of variation in appearance, especially if they are tarnished.
Space does not permit including photos of all the different sulfides, but some examples are below. The most common gold and goldish sulfides are pyrite, chalcopyrite, and pyrrhotite shown in Figures below. They can be very hard to tell apart. Figures 3. Chalcopyrite, in contrast with pyrite, contains copper and easily tarnishes — often to a yellow green color. The photo of chalcopyrite below Figure 9. Chalcopyrite is much softer than the other two minerals which also sometimes helps identification.
Pyrrhotite, seen in Figure 9. Some pyrrhotite has a more silvery color than pyrite which helps identification. The photos below show examples of galena Figure 9. The lusters of the samples in these photos are not particularly metallic, but many specimens of these minerals are. For example, Figure 3. Copper minerals are often characterized by strong colors. Bornite, which is unremarkable and hard to identify if unoxidized, commonly oxidizes to form what we call peacock ore Figure 9.
Covellite Figure 9. We include a photo of azurite and malachite here Figure 9. But azurite and malachite are secondary copper carbonate hydroxides and not sulfide minerals. Both minerals are hydrated carbonates. Sphalerite ZnS is a mineral that has many different appearances; the three photos below show examples. Gray galena and orange dolomite are also present in the photo. Because of its many different appearances, sphalerite can be hard to identify unless it is brown and resinous as in Figure 9.
For example, Figures 3. The many different colors of sphalerite are due to trace amounts of iron and other elements in the zinc sulfide. In laboratories, pure manufactured zinc sulfide is white. We typically identify these minerals by their color. Cinnabar Figure 9. Realgar Figure 9. Note that the orpiment contains a small amount of orange realgar; their compositions are nearly identical.
The small gray triangular diagram in the top of Figure 9. The blue region in the center of the triangle is where compositions of the most important ore minerals plot.
The quadrilateral below the triangle is an enlargement of that blue region. The quadrilateral shows seven minerals. Bornite and pyrrhotite, which have variable compositions appear as bars that show the variation. Different specimens of bornite may contain different amounts of copper and iron, and so bornite plots as a horizontal bar. Pyrrhotite contains variable amounts of iron and sulfur and so plots as a bar pointing at the iron and sulfur corners of the triangle.
The other minerals do not vary much in composition and so appear as dots. The phase rule discussed in Chapters 4 and 8 tells us that the number of minerals that can coexist is generally quite small for simple chemical systems.
This triangle depicts a simple system with only three chemical components. Tie lines and triangles on the quadrilateral show minerals that may be found together. If, for example, a rock has composition that plots where the number 3 is, it will contain bornite, chalcopyrite, and pyrrhotite. Cu-Fe sulfide mineralogy is complex because many minerals have similar compositions.
The quadrilateral shows 10 triangular fields numbered 1 through Those in light blue are 3-mineral fields — any composition that plots within them will contain three sulfides.
The darker blue triangles only connect two minerals; they are 2-mineral fields. Compositions that plot within them will contain only two sulfides. The assemblage present in a specific deposit depends on the Cu:Fe:S ratio. In Fe-poor ore deposits, for example, sulfide assemblages will include covellite, digenite, or chalcocite, but not pyrite or pyrrhotite. Diagrams such as the one in this box Figure 9. The table to the left lists the most common of these minerals.
These minerals often have similar properties, and most have relatively simple and related formulas. Oxide minerals consist of metal cations bonded to O Hydroxide minerals contain OH — anion molecules in place of all or some O We group quartz, the most common oxide, with silicate minerals, so it is not considered here.
A primary difference between oxides and hydroxides is the temperatures at which they form and are stable. Hydroxides are unstable at high temperature; they exist in low-temperature environments and are commonly products of alteration and weathering. Other oxide minerals — magnetite and ilmenite, for example — are high-temperature minerals generally associated with igneous or metamorphic rocks.
In fact, most igneous and metamorphic rocks contain oxide minerals. Typically they are present in minor amounts, are easily overlooked, and may be difficult to identify. Oxides and hydroxides have properties distinct from silicates and sulfides.
They are often dominated by ionic bonding, and anions O 2- or OH — do not control their structure and properties as anions do for other mineral groups. Oxides and hydroxides also are distinct from carbonates, sulfates, and other ionic minerals that often have relatively high solubilities in water. The different formulas reflect different valences of the metal cations. Oxides with general formula XY 2 O 4 spinel and chromite in the table belong to the spinel group ; they all have similar atomic arrangements but contain different elements.
Some oxide minerals, for example corundum and spinel, come in many colors. Sapphire may be other colors too, including white, pink, yellow, or orange. The photos below show four different colored spinels that were cut as gems.
Pure spinel which is rare is clear or light gray like the stone in Figure 9. Spinels may be various shades of red, purple, blue, yellow, orange, pink, or black, but red is most common. Some examples are in Figures 9. Some typical samples are in the photos below.
Magnetite Figure 9. It is the only strongly magnetic mineral, which aids identification considerably. Hematite may have a metallic silver color Figure 9.
Goethite Figure 9. The photo is The photo is 8 cm across 9. It sometimes looks like an iron oxide magnetite or hematite but is nonmagnetic and has a black streak.
The hexagonal flakes of ilmenite in Figure 9. Cassiterite, tin oxide, is shown in Figure 9. It is harder than the other minerals shown and often has an adamantine luster. It shares properties with the other three minerals. The black arborescent mineral in Figure 9.
Dendritic pyrolusite is sometimes mistaken as having an organic origin. Pyrolusite has other appearances and may be difficult to distinguish from other dense dark-colored minerals.
But, it is the only common mineral that forms dendrites like the ones shown. Gems are precious or semiprecious stones and related substances that we can cut or polishe to use for ornamentation. There are many kinds, and they may be natural or synthetic. Most gems are natural materials; they can be either minerals or nonminerals. The term gemstone is sometimes used to refer to gems that are minerals. The table lists the common gemstones and their most important countries of origin.
Only one or two countries dominate production of many gems, including diamond. Because gems differ in appearances from common minerals, they often have names different from their mineral names. The table contains some examples. Diamond, emerald a variety of beryl , and ruby a variety of corundum , have been, historically, the most valuable gemstones. Sapphire another variety of corundum and alexandrite a variety of chrysoberyl are nearly as valuable.
It was a unique oval-shaped diamond with a vivid pink color, weighed about 60 carats, and was almost 2 cm in longest dimension. It is not the composition of gems that makes them valuable, but rather their appearance. Most are varieties of common minerals that exhibit spectacular color, clarity, brilliance, or play-of-color.
The hardest gems — for example diamond, ruby, and sapphire — are especially highly valued because they are most durable. Common beryl, is opaque with a nondescript blue color. For an example, see Figure 6. But exceptional beryl crystals are beautiful translucent or transparent gems, including emerald green , aquamarine blue , morganite pink , helidor yellow , goshenite clear , and several other varieties. The four photos below 9. Although common beryl has no value as a gem, it is sometimes mined as a beryllium ore mineral.
Other photos of gemmy beryl were seen in Figures 1. The green crystal is 2 cm long 9. Fire is most apparent in minerals that exhibit dispersion — the ability to separate white light into different colors that pass through the mineral along slightly different paths.
Diamond best exhibits this property Figure 9. Fire is most notable in clear gemstones and may be completely masked in strongly colored stones. Fire may also be seen in amber or pearls — which we call gems although they are not minerals. Proper polishing or cutting can enhance play-of-color in gems of many sorts. Gems and other minerals derive their color from many different things see Chapter 3. Common minerals may have little value as gems, but if we can alter or enhance colors, even common quartz may become valuable.
Gemologists, therefore, often treat gems and minerals, natural or synthetic, to change or enhance their color and increase their value.
The vast majority of gems on the market today have had their appearances enhanced in some way. For instance, quartz crystals from the Hot Springs area of Arkansas are irradiated to disrupt their atomic structure and give them a smoky, purple, or black color. Irradiation is also used to induce color changes in diamond and topaz. The strong color was produced by irradiation. Gemologists have successfully used heat treatment — which changes elemental valences or alters atomic structures — on quartz, beryl, zircon, and topaz, although the results are not always predictable.
Today, it is routine to synthesize gems of many sorts, including diamonds, and also varieties of quartz, beryl, corundum, and garnet. Chrysoberyl, opal, rutile, spinel, topaz, and turquoise are also synthesized.
We saw photos of both natural and synthetic topaz and ruby in Figures 1. The photos seen here in Figure 9. Several synthetic compounds with no natural equivalents are used as simulants for gems.
Today, clear CZ — two examples are seen in the photo — is the most common diamond simulant. CZ can have just about any color and so is a common simulant for other, darker-colored, gems as well.
Gem manufacturers use several different methods to produce synthetic crystals. The Verneuil process and the Czochralski process both involve crystallizing gems from molten material Figure 9. In the more common Verneuil process, powdered starting materials pass through a hot furnace and melt to produce droplets that add to a growing boule , a single elongated crystal, at the bottom of the furnace.
The boule is slowly withdrawn from the furnace as it grows. This technique produces large synthetic rubies, sapphires, spinels, and other gems. The synthetic rubies are often key components of lasers. In the Czochralski process also shown in Figure 9. As it grows, the crystal is raised from the melt and so grows even longer. The photo on the left, below in Figure 9. The other colored stones are generically called sapphire.
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