GO 340 Gemstones & Gemology

Emporia State University
Susan Ward Aber

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).

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-karat Gold Jewelry Techniques

  • Gold filled, gold overlay: A layer of 10K gold or better can be mechanically bonded to all significant surfaces. The layer of gold must be at least 1/20th of the total metal weight or it cannot be described as gold filled (typical mark 1/20th 12K GF or 12 Karat Gold Filled).
  • Gold plate, rolled gold plate: This is the same as gold filled except the quantity of karat gold may be less than 1/20th of the total metal weight (typical mark 1/40th 12K RGP).
  • Gold electroplate: An electrolytic process where a coating of gold of not less than 10K fineness, with a minimum thickness equivalent to 7 millionths of an inch.
  • Vermeil: Gold with a minimum fineness of 10K mechanically bonded or electroplated over a base of sterling silver, with a thickness of gold at least 120 millionths of an inch.

    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
    Country millions of troy ounces
    South Africa 19.2
    United States 9.6
    CIS 7.8
    Australia 7.5
    Canada 5.7
    China 3.5
    Brazil 2.4
    Papua New Guinea 1.9
    Colombia 1.1
    Chile 1.0

    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
    State troy ounces in 1991 troy ounces in 1992
    Nevada 5,700,758 5,871,994
    California 960,447 1,006,326
    Montana 594,794 472,523
    Idaho 107,642 103,494
    Alaska 102,755 Withheld
    Colorado 102,272 Withheld
    Arizona 66,488 198,886
    Other States 1,684,552 1,886,879
    Total 9,320,093 9,540,134
    Withheld: Withheld to avoid disclosing company proprietary data

    Other States include: Michigan, New Mexico, Oregon, South Carolina, South Dakota, Utah, & Washington.

    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

    Gold Exploration

    Large mining companies spent an estimated $839 million searching for gold in 1992, down 16% from $1 billion in 1991. Falling metal prices and budget cuts were attributed to the decline. The largest share of gold exploration was spent in the U.S. (21.4% of the total metal exploration), followed by Australia (19.1%), and Canada (17.8%).

    U.S. Gold Supply in 1992
    Supply Troy ounces
    Primary refinery production 8,969,788
    Secondary (old scrap) production 4,192,483
    Imports (refined only, non monetary) 4,269,806
    Deliveries from foreign accounts* 5,736,456
    Stocks decrease (industrial and futures)896,876
    Total Supply 24,065,409

    U.S. Gold Distribution in 1992
    Distribution Troy ounces
    Consumption in arts and industry3,558,407
    Exports (refined and non monetary gold)10,927,123
    Deliveries to foreign accounts* 1,351,358
    Stock increase (industrial and futures) 162,265
    Total Distribution 15,999,153
    Apparent Surplus 8,066,256

    * Gold held for foreign and international official accounts at the New York Federal Reserve Bank.

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    SILVER

    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 (http://minerals.usgs.gov/minerals/pubs/commodity/silver/silvemcs04.pdf). Silver is primarily used in the photographic industry and as digital cameras improve in quality and popularity, the silver industry as a whole will suffer. Silver use has fallen for the fourth successive year (http://minerals.usgs.gov/minerals/pubs/commodity/silver/silvemcs04.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. Vermeil is sterling silver jewelry electroplated with karat gold.

    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.

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    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%.)

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    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 (saber@emporia.edu).

    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: saber@emporia.edu Thanks for visiting! Webpage created: February 2, 2000; last update: February 22, 2009.

    Copyright 1999-2009 Susan Ward Aber. All rights reserved.