GO 340 Gemstones & Gemology
ES 567 Gemstones of the World
Dr. Susan Ward Aber, Geologist & Gemologist
Emporia State University
Emporia, Kansas USA

http://www.emporia.edu/earthsci/amber/go340/gold.htm

Precious Metals

The precious metals are gold, platinum, and silver. They are all rare, with gold present in 3.5 parts per billion of the Earth's crust, platinum about 45 parts per billion, and silver in 73 parts per billion. These metals are strong and heavy because of their close-packed atomic structures and metallic bonding. Gold's specific gravity is 15-19.3 (density of 11 ounces per cubic inch). Silver's specific gravity is 10.5 (6.25 ounces per cubic inch). Platinum's specific gravity is 14-19. Osmium, a sister metal of platinum, is the heaviest metal on Earth with one cubic foot weighing three quarters of a ton! (St. John, 1984, p. 126).

Gold

Silver

Platinum

Precious Metal Facts

GOLD

Gold is found on Earth and an equal amount is present in sea water, but very expensive to extract. It does not rust or corrode and combines beauty with easy workability, rarity, and virtual indestructibility to be a fascination to civilizations throughout time. Goldsmiths and tools were few in ancient civilizations and they worked only for the royalty and very wealthy. Today goldsmiths have machines as well as hand techniques to work the metal and make it possible for just about everyone to own and wear karat gold jewelry.

"Eighty percent of world gold production goes to gold jewelry" (JCK online, May 10, 2004). Gold is soft or can be scratched easily, and it has a malleable and ductile tenacity. Gold has a hardness of 2.5-3 and one troy ounce of gold (around the size of a sugar cube and equal to about 31 grams) can be hammered into a sheet (called gold leaf) covering 108 square feet or pulled into a thread fifty miles long. Gold is a pure state is too soft for use in jewelry. Because of gold's softness and malleable tenacity, it is mixed or alloyed with other metals to make it strong and keep it from bending too readily. Prongs of 20-24K gold are usually not strong enough to hold the gem securely, unless it is "gold 990" or an alloy of gold (90%) and titanium (10%) (Matlins and Bonanno, 1998, p. 206).


Monkeys support the stairway to
heaven on the grounds of the
Grand Palace, Bangkok, Thailand.
Photo by S.W. Aber, 9/2008.
Grand Palace, Bangkok, Thailand.
Photo by S.W. Aber, 9/2008.

Karat is a measurement of fineness or purity of gold and abbreviated "K" or "KT." Pure or fine gold is 24 karat or by the European system, 1000 points fineness. If the gold is 24 karat, 24 parts out of the total are gold. If gold is 18 karat, 18 parts of the whole are gold and 6 parts are some other metal. In other words, 18 karat is 75% gold (18/24 = 3/4).

Gold Measure
Karatage Gold Content Fineness
24K 100%1000
22K 92% 916
20K 83% 833
18K 75% 750
14K 58% 585
12K 50% 500
10K 42% 417
9K 38% 375

Many countries have a minimum karat standard for an item to be called gold. The minimum legal standard of karatage in the U.S. is 10K. Anything less than 10K can not be called gold. The minimum standard for Canada and England is 9K, Mexico is 8K, and in Italy and France, 18K. In the U.S., gold articles do not have to carry a karat or other quality mark. However, if a karat mark is applied, it must be registered (manufacturer's registered trademark stamped near the karat mark) and accurate in accordance federal law.

An alloy, or mixture of metals, is not only to produce optimum strength, but also color. Various metals are mixed with gold to produce stronger jewelry and different colors. White gold is often plated with rhodium, a sister metal to platinum, to give it a whiter finish.

Gold Colors
Gold Color Elements Alloyed with Gold
Yellow Gold-Au, Copper-Cu, Silver-Ag
White Gold-Au, Nickel-Ni, Palladium-Pd, Platinum-Pt, Zinc-Zn
Green Gold-Au, Silver-Ag, Copper-Cu, Zinc-Zn
Pink Gold-Au, Copper-Cu

Karat Gold Jewelry Techniques
  • Hand fabrication is used when detailed designs make it impossible to mass produce the piece. Gold shot, or gold metal grains of any karatage, is used to create gold in sheets or wire that is pulled through a draw plate. The design is created on paper, cut out and glued onto gold sheet. A jeweler's saw is used to cut out the patterned pieces. The design is pierced or cut into the shape, bent and hammered, and finally soldered with karatage melt. The soldering process bonds metal to metal by the use of heat and a filler metal called solder. Filing, sanding, and polishing complete the process. As a final step, the karatage of the metal is stamped into the piece and the jewelers personal goldmark logo to guarantee quality. Precious metal markings and hallmarks can show where the piece was made and how old it is, by identifying the guild, town, country, or company.
  • Lost wax casting has been practiced for some 6000 years and the method lends itself to mass production today. A model of the finished product is carved in wax and positioned in a container. The "investment" is poured in, surrounding the design. The mold is heated, which melts the wax and creates a perfect mold or hollow form of the original design. The mold is then filled with gold or silver, creating a perfect cast of the design. Lost wax casting will be the subject of the next lecture.
  • Die striking produces a stronger product than casting the metal and is often used for prong settings of a ring. Gold is malleable and the design can be stamped, cut, or formed with the proper machinery. Die struck and cast items can be soldered together for a variety of combinations.
  • Gold electroforming could be equated to a paper-mache ball created by wrapping strips of plastered paper around an inflated balloon. When the paper hardens the balloon is popped, leaving a hollow sculpture. Electroforming uses gold particles electrostatically applied to a wax or silver form (called a mandrel) that is later removed. It is a process that allows large but lightweight gold jewelry; it is hollow with seamless surfaces virtually impossible to do in standard manufacturing processes. In theory lightweight gold electroforming should mean lower prices, but until recently the process was only done by Israeli & European manufacturers. Now, technology and new equipment has brought electroforming to the mass market and the U.S. is playing a leading role.

    Non-Solid Gold Jewelry Techniques

    Even though pure gold is alloyed with other metals, which is measured as karated gold, it is solid gold according to the FTC ruling from 1967. In other words, the metal is a mixture of varying amounts of gold, but it is still a solid mixture throughout. The antithesis of this is a gold imitation or the process of encasing a base metal in gold. The former is not gold and the latter, not solid gold but rather a thin veneer of karated gold. The most common gold imitation is a mixture or alloy of zinc, copper, and tin that create a yellow colored metal. Metal can also be given a gold wash or finish. The base metal is brass or steel and the product is electroplated with a non-standardized thickness of gold. Encasing a particular base metal in gold goes by several names that reflect the application method of the gold overlay, plating, or elecrolytic process.

    Gold Facts

    For statistics and general information on gold, visit these external webpages:

    Although the statistics presented below are dated, they still provide an idea of gold producing countries. In a JCK article (May 10, 2004), Peru was listed as the sixth biggest gold producer in the world. This country is changing laws to encourage more gold mining and manufacturing, and gold will be exchanged as a local commodity for the first time in Peru (JCK online, May 10, 2004).

    Top Ten Producers of Gold
    in 1991 (left) and 2008 (right)
    Leading Country in 1991 millions of troy ounces Leading Country in 2008 percent of world production
    South Africa 19.2 China 12.2%
    United States 9.6 United States 9.9%
    CIS 7.8 South Africa 9.8%
    Australia 7.5 Australia 9.6%
    Canada 5.7 Peru 7.4%
    China 3.5 Russia 7%
    Brazil 2.4 Canada 4.2%
    Papua New Guinea 1.9 Indonesia 3.8%
    Colombia 1.1 Uzbekistan 3.6%
    Chile 1.0 Ghana 3.4%
    Other Other 29%

    The 2008 leading country information is detailed at Gold InfoMines, http://gold.infomine.com/countries/. Top producers in the U.S. are shown below. The number of tons produced was taken from hubpages.com/hub/largest-gold-producer. Although North Carolina is not a leader in the 21st century, gold was mined there in the past. A rich account is given at www.geology.enr.state.nc.us/Default.htm, a website link from the North Carolina Geological Survey (www.geology.enr.state.nc.us/Default.htm).

    Mine production of gold reported by the USGS for January-November, 2003, showed statistics for California-4090 kilograms, Nevada-206,000 kilograms, and other states-42,000 kilograms (Mineral Industry Survey, from http://minerals.usgs.gov/minerals/pubs/commodity/gold/pmmis1103.pdf. Other states mining gold but not reporting quantities include Alaska, Arizona, Colorado, Idaho, Montana, New Mexico, South Carolina, South Dakota, Utah, and Washington. Although the data below is dated, I will leave it on for now to show which states have been active producers and to what extent.

    U.S. Gold Mining
    in 1991-1992 (left) and 2007 (right)
    Leading Gold Producing State 1991-2 troy ounces in 1991 troy ounces in 1992 Leading Gold Producing State 2007
    Nevada 5,700,758 5,871,994 Nevada
    California 960,447 1,006,326 Alaska
    Montana 594,794 472,523 Utah
    Idaho 107,642 103,494 Colorado
    Alaska 102,755 Withheld Montana
    Colorado 102,272 Withheld South Dakota
    Arizona 66,488 198,886 California
    Other States 1,684,552 1,886,879 Other States
    Total 9,320,093 9,540,134 Total

    In 2007, Nevada was responsible for producing 78% of the all the gold mined in the U.S. and this information was from the USGS Commodity Yearbook, minerals.usgs.gov/minerals/pubs/commodity/gold/myb1-2007-gold.pdf. In the table above, the Withheld designation is to avoid disclosing company proprietary data

    Other States in the 1990s included: Michigan, New Mexico, Oregon, South Carolina, South Dakota, Utah, & Washington. In 2007, other included New Mexico, Arizona, and Idaho, in descending order of production.

    U.S. Consumption of Gold by End Use 1991-1992
    End Use 1991 (thousands of troy ounces) 1992 (thousands of troy ounces)
    Jewelry and arts, karat gold 2,568 2,612
    Jewelry and arts, electroplating 12 9
    Jewelry and arts, gold filled and other uses 123 114
    Jewelry and arts, Total 2,703 2,735
    Dental, Total 273 213
    Industrial, karat gold 34 35
    Industrial, electroplating 406 326
    Industrial, gold filled and other uses261 239
    Industrial, Total 701 600
    Grand Total 3,677 3,548

    In 2009, jewelry continues to be the greatest end use consumption, followed by electronics and dentistry; investments are grouped as bar hoarding, official coin, medals/imitation coin, and other retail investment (www.research.gold.org/supply_demand/).

    return

    SILVER

    February 18, 2011 was a monumental day. It was Sarajane and Ken Aber's 60th wedding anniversary! However, more germane to this course is that on this date silver prices rose to $32.83 an ounce, the highest level in 31 years! The political unrest in the Middle East and northern African nations - Egypt, Jordan, Algeria, Tunisia, Libya, Morocco, Yemen, Bahrain, to name a few - is to blame for higher metal and oil prices as a democratic will of people plays out through the use of Internet, Twitter, Skype, and Cellular Phone communication technologies. Some are predicting the prices of metals and oil will continue to rise throught 2011 (http://www.jckonline.com/2011/02/21/silver-prices-hit-31-year-high). In the past, the price of silver was artifically driven up by Nelson and William Hunt, brothers who tried to corner the market on silver and were responsible for a previous high of $50.00 an ounce, by March 7, 1980. The Hunt brothers acquired silver through silver futures contracts and silver bullion from 1979 and 1980; the price, for no apparent industry or jewelry demand, went from $11 an ounce in September 1979 to the high of $50 an ounce in early 1980 (http://en.wikipedia.org/wiki/Nelson_Bunker_Hunt). Silver prices collapsed to below $11 an ounce on March 27, 1980 which would later be referred to as Silver Thursday (http://en.wikipedia.org/wiki/Silver_Thursday). Although it is reported the Hunt families lost over a billion dollars, their fortunes remained intact. In 1988, the brothers were convicted of civil charges for conspiracy to corner the silver market and were ordered to pay $134 million compensation fines to a mineral company in Peru, which eventually forced the brothers to declare bankruptcy.

    Silver is an element that occurs naturally in the Earth and in pure form, although it is too soft for practical use. Two-thirds of silver is found in association with copper, lead, and zinc, while the remainder is mined from gold-silver vein deposits (minerals.usgs.gov/minerals/pubs/commodity/silver/silvemcs04.pdf). In 2006, Alaska was the leading producer of silver in the U.S., followed by Nevada (http://minerals.usgs.gov/minerals/pubs/commodity/silver/silvemcs07.pdf).

    Important physical properties for silver include ductile and malleable tenacity, high electrical conductivity, and reflectivity. Traditional use categories for silver include photography, silverware, jewelry, as well as medals and coins, and industry. The demand for silver continues with industry and silver is used

    in bandages for wound care, batteries, brazing and soldering, in cell phone covers to reduce the spread of bacteria, in clothing to minimize odor, in catalytic converters in automobiles, electronics and circuit boards, electroplating, hardening bearings, mirrors, solar cells, wood treatment to resist mold, and water purification. main components of dental amalgam, are biocides and their use in amalgam inhibits recurrent decay (http://minerals.usgs.gov/minerals/pubs/commodity/silver/silvemcs07.pdf).
    The newest use of silver is ..."for miniature antennas in Radio Frequency Identification Devices (RFIDs) that were used in passports and on packages to keep track of inventory shipments (http://minerals.usgs.gov/minerals/pubs/commodity/silver/silvemcs07.pdf).

    With regard to the jewelry industry, "sterling" stamped on a piece means it meets the U.S. government standard for solid silver (92.5% silver and 7.5% of another alloy, such as copper added for strength). The ".925" mark also designates sterling silver. Silver plate is a combination of base metal, such as brass, with a plating of pure silver bonded in an electrolytic process. Sterling silver can look antique as time passes and a patina forms. Also, sterling silver jewelry electroplated with karat gold and referred to as vermeil.

    Just as gold can be a thin veneer over a base metal, the same is done with silver. Silver filled or overlay is sterling that is mechanically bonded. The layer must be equal to at least 1/20th of the metal in a setting. Silver plate (SP) is a fine silver film deposited over a base metal by electrolysis; the industry standard is .15 to .25 mils in thickness. The veneer, like gold, can be as thin as seven millionths of an inch. A silver plate item cannot be marked as silver. A silver wash or finish is electroplating over base metal of brass or steel but without restriction on the thickness.

    Other white metals include nickel and nickel plated. Nickel is malleable and resists oxidation; this is desirable because oxidation is the common causing allergic reaction. Nickel Silver resembles sterling silver and is an alloy but mostly containing nickel. It is popular in Germany and US with Native American jewelry. Nickel-plating is popular and must comply with industry standards with a thickness of .15 to .25 mils thickness of nickel, which is plated to a base metal.

    One white metal often used in costume jewelry is the silver alloyed with tin or lead. This pewter/silver mixture is known as tin plate or Britannia metal.

    Another white silver look alike is niobium - this is...

    a hypo-allergenic metal first engineered to protect hypersonic aerospace vehicles from extreme conditions. After manufacturing into the desired shape, such as earwires, headpins, eyepins or jumprings, the naturally grey base metal niobium is then anodized to create six signature colors. Most people who are metal-sensitive can comfortably wear niobium (Fire Mountain Gems & Beads dictionary, www.firemountaingems.com/encyclobeadia/beading_results.asp?PageNo=1&kwsearch= &numOfResults=20&doccat=glossary).

    Finally, stainless steel resists corrosion and is the other white jewelry material being used. It often contains more than 10% chromium, and may also contain varying additions of nickel, molybdenum, titanium, niobium and other elements. The other type has some molybdenum included.

    Silver is much less expensive than gold and platinum. The ease of working with silver makes it a favorite among jewelry designers. Mr. Ernie Herrick presented the lost wax casting technique working with to the class, which will be the subject of the next lecture (Working With Silver).

    Silver Facts

    For statistics and general information on silver, visit these external webpages:

    Mine production of silver reported by the USGS for January-November, 2003, showed statistics for Nevada (295,000 kilograms), and other states (833,000 kilograms) (http://minerals.usgs.gov/minerals/pubs/commodity/gold/pmmis1103.pdf). Other states mining silver but not reporting quantities include Alaska, California, Colorado, Missouri, Montana, New Mexico, New York, South Carolina, South Dakota, Tennessee, Utah, and Washington. In 2003, Alaska became the leading producer, displacing Nevada according to the USGS reporting (http://minerals.usgs.gov/minerals/pubs/commodity/silver/silvemcs04.pdf). Although the data below is dated, I will leave it on for now to show which states have been active producers and to what extent.

    U.S. Silver Mining
    State 1991 (troy ounces) 1992 (troy ounces)
    Nevada 18,583,278 18,872,637
    Idaho 10,834,887 8,134,203
    Montana 7,137,522 6,269,445
    Arizona 4,758,348 4,983,405
    Missouri 1,125,285 803,775
    Colorado 643,020 417,963
    California Withheld 482,265
    Other States 16,268,406 16,011,198
    Total 59,415,048 55,974,891

    Other states that mine silver include: Alaska, Illinois, Michigan, New Mexico, New York, Oregon, South Carolina, South Dakota, Utah and Washington.

    return

    PLATINUM

    Platinum hammered strip was set into a gold and silver box from Thebes, fashioned in the Seventh Century B.C. and some flecks appear in gold Egyptian pieces from 1400 B.C. (St. John, 1984.p. 118). Some 2,000 years ago, South American Indians were the first to work and mine platinum, creating nose rings and jewelry items with a smelting process that would remain secret until the late 1700s.

    Platinum was introduced in jewelry settings by Louis Cartier in the 1890s (St. John, 1984, p. 117). Platinum is more rare on Earth than gold and silver. Platinum jewelry is often alloyed with other members of the platinum family, iridium or ruthenium, to add strength. Rhodium, another platinum member, is the most reflective or bright of the metals and is used to coat or plate gold and platinum jewelry.

    Although platinum is identified by karat marks but stamped with "PT" or "plat" in the U.S. and "950" or "PT950" in Europe, other alloys are coming on the market. Dave Neuberg, Chief Executive Officer for Karat Platinum, put in a request to the Federal Trade Commission (FTC) to accept new technology for producing 585 platinum and 415 copper and cobalt product, 585 Plat.0 PGM, which will be stamped 585Pt.415Co.Cu (http://www.ftc.gov/os/comments/jewelryplatinum/517683-00054.pdf. ). This alloy stamp means the Karat Platinum is 58.5 percent platinum, and 41.5 percent copper and cobalt. Read more about this at http://jewelrymaking.about.com/od/aboutmetalandstones/a/070205.htm and follow links to the related articles as well. The Diamond Guy Diamond Cutters International refers to this controversy as platinum doping (http://www.diamondcuttersintl.com/diamond_education/articles/reference/platinumdoping.html. For extensive articles on working with platinum-palladium visit http://www.ganoksin.com/.

    South Africa supplied nearly two-thirds of the world's platinum. Political and labor unrest affects the price of platinum and periodically causes a rise in the price. The price very rarely trades below the price of gold.

    For statistics and general information on platinum, visit these external webpages:

    Platinum Supply
    Country 1989, thousands of troy ounces 1991, thousands of troy ounces
    South Africa 2,580 2,770
    North America 210 220
    Others 50 70
    Russian sales 440 1,110
    Total Supply 3,280 4,160

    Platinum Demand in the Western World 1991
    Use % of total demand
    Jewelry 36%
    Auto catalysts 33%
    Investment 10%
    Chemical 6%
    Electrical 5%
    Petroleum 4%
    Glass 3%
    Other 3%
    Total 100%

    (In 1988, jewelry was 30% of demand and auto catalysts were 36%.)

    return

    Precious Metal Facts

    Metal Prices
    Month/year Gold/troy ounce Silver/troy ounce Platinum/troy ounce
    1/1988 $458.00-483.90 $6.50-7.65 $475.00-509.00
    1/1989 $394.00-411.60 $5.82-6.17 $526.00-532.00
    1990 $472.00-503.00 $5.18-5.34 $395.00-418.75
    1991 $366.00-403.00 $3.79-4.23 $393.00-412.00
    1992 $348.65-357.20 $4.05-4.22 $349.50-369.50
    1993 $328.25 $3.64 Not available

    Imports of Precious-Metal Jewelry
    Country of Origin 1991
    Italy $1,024,543,000.00
    Thailand $228,683,000.00
    Hong Kong $221,660,000.00
    Isreal $208,434,000.00
    India $101,924,000.00
    Peru $100,707,000.00
    Dominican Republic$99,706,000.00
    Mexico $38,539,000.00
    Canada $34,663,000.00
    Bolivia $26,829,000.00
    Korea $24,169,000.00

    Exports of Precious-Metal Jewelry
    Country of Destination 1991
    Japan $48,869,000.00
    Thailand $39,955,000.00
    Switzerland $31,014,000.00
    Canada $25,916,000.00
    Germany $15,896,000.00
    Bolivia $14,634,000.00
    Mexico$14,277,000.00
    Hong Kong$13,545,000.00
    United Kingdom $12,286,000.00
    Panama $9,866,000.00

    Several past mineralogy students have created very nice webpages on precious metals, including:

    Metal Testing Equipment Supplier

    Students enrolled in this course should email me first when considering any purchases (abersusie@gmail.com).

    The material for this section came primarily from:

    • Return to the Syllabus or go on to the next lecture.

    This page originates from the Earth Science department for the use and benefit of students enrolled at Emporia State University. For more information contact the course instructor, S. W. Aber, e-mail:abersusie@gmail.com Thanks for visiting! Webpage created: February 2, 2000; last update: September 29, 2011.

    Copyright 1999-2011 Susan Ward Aber. All rights reserved.