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Gold
Michelle Simmons
Physical Geology
Fall 2005

                                             The Native Element Gold

           

                                                      

            The native, chemical element, Au (gold) is a highly esteemed metal.  Yellow in color, this soft but weighty metallic element is not only known for its beauty.  It also has high levels of ductility as well as malleability.  One piece of gold can be hammered and compressed into a thin sheet, as well as other shapes, with measurements of five meters on either boundary. On Mohs Scale of Hardness, gold has a hardness rating of 2.5-3.  Knowledge of Gold’s existence dates back to primeval times.  Steve Gagnon, of Jefferson Lab, states that, “Gold is sometimes found free in nature but it is usually found in conjunction with silver, quartz (SiO2), calcite (CaCO3), lead, tellurium, zinc or copper.” http://education.jlab.org/itselemental/ele079.html
 

                                                   gold in quartz-credit photo to R.Weller/Cochise College.  

      

            When native gold is mixed with additional metals its strength is amplified. Gold, known for its attractiveness, has many other widespread uses.  One use, when mixed with other metals, is to manufacture coins, jewelry, and ornamental objects.  The mixing together of gold and other metals such as copper, platinum, and silver is known as alloy.  The native element gold is broadly allocated in our Earth’s crust at a backdrop concentration of 1000 kg/0.03g.

 

                                                                                                 photo of my jewelry
 

“Karat” vs. “Carat”-- When pureness of gold in alloy is measured, it is measured in components labeled Karats.  Carat is the measurement of how much something weighs: 1 carat = 1/5 gram, 1 oz. = 27 grams, and 1 oz. = 140 carats.  24 karat is pure gold.  Gold alloy has a reddish tint to it. As jewelry, gold has existed well over 6,000 years and shoppers need or desire for gold exceeds 20% each year.  Buyers, when looking to purchase gold should select something that’s 14K. 14K is 10 fractions of other metals and 14 fractions of gold. 

 

 

                                               gold in quartz-credit photo to R. Weller/Cochise College

     Gold does not oxidize or tarnish in normal conditions.  The element symbol for gold, Au, comes from Latin expression “aurum,” which means shining dawn.  Other facts about gold are as follows: Atomic number: 79, Atomic mass: 196.966569(4) g/mol, Density: 19.3 grams per cubic centimeter, Fluid density: 17.31 grams per cubic centimeter, Room temperature stage: solid, Sweltering (boiling) point: 5,173 degrees Fahrenheit, Liquefying point: 1,947.52 degrees Fahrenheit, Categorization element is Metal, Heat capability: 25.418 J/(mol*K), Temperature of heat vaporizing: 324kJ/mol. 


finely crystallized gold-credit photo to R.Weller/Cochise College.
specimen courtesy of Brander Robinson
  
branderrobinson@msn.com


     Gold also has an estimated maximum stretching force of 19,000 pounds per square inch.  It has no cleavage or fracture and has a specific gravity of 19.3, when it is pure gold.  Gold’s specific gravity has a range of 15.6 to 19.3.  Gold comes in different assortments of colors such as, green and white alloy where silver is prevalent.  When alloyed with copper, the color is or becomes red.  Gold also has a crystal formation that is cubic face centered.  Native gold customarily includes a percentage of silver ranging from eight to ten but may also include a great deal more.  The more silver native gold includes the whiter it grows to be.  The more silver native gold has also lowers the specific gravity.

     Gold arises in elevated concentrations and is also common in low concentrations in all igneous rocks. There are two basic manners of elevated concentrations: placer deposits and hydrothermal veins or reefs.  Hydrothermal veins of gold appear in metamorphic and igneous rocks.   In placer deposits, gold develops from eroded rocks that contain gold that appear in streambeds and alluvium.  Hydrothermal veins are associated with fool’s gold (pyrite) and the mineral, quartz.  Minuscule portions have also occurred in most rocks and soils.  In saltwater gold may appear at 0.1 to 2 mg; this depends on where a sample is taken.
 

   A gold nugget Gold ore

   credit photo to Wikipedia:  http://en.wikipedia.org/wiki/Gold

    
Gold has many uses and values.  Besides jewelry, gold is used in dentistry, and medicine.  Gold plays a large role in various industrial developments.  Gold serves as a superb conductor of electricity and heat.  It also can be turned into thread used in sewing, needlework, and stitching.  Gold carries out essential tasks in communications equipment, computers, jet aircraft engines, spacecrafts, telescopes, lasers, and many other manufactured goods.  Gold also plays an intricate role in today’s economical stature.  Gold is used as currency, as a means of exchange for trading of assets, commodities, securities, and/or other marketing operations, by many different nations/countries.
 

Gold bars with krugerrands in the background. Three Gold Sovereigns with a Krugerrand

credit photo to Wikipedia:   http://en.wikipedia.org/wiki/Gold

     When trying to determine if something you have found is the native element gold, using a test called “streak test” can be very helpful.   A streak test is an easy test you can perform.  This test is provided by Desert Gold Diggers: Identifying Gold.  
“A good test is to look at the streak of a mineral. This is the color observed when the mineral is crushed into a fine powder and then placed on a white sheet of paper. A more convenient method is to rub the mineral across a tile of unglazed white porcelain, called a streak plate, and noting the color of the streak. See the following chart. Note that this test can only be used on minerals that do not exceed the hardness of the streak plate, about 6 1/2."  There is also another test provided by Desert Gold Diggers.  This test is viewable at the link following the chart: "Selected Minerals and their streak color."
 

Selected Minerals and their streak color

Mineral

Streak Color

Gold

yellow or gold

Pyrite

greenish black

Chalcopyrite

greenish black

Arsenopyrite

grayish black

Micas

colorless

http://home.att.net/~desert-gold-diggers/gold/goldtests.htm
 

 

    

http://images.google.com/images?q=gold+photos&hl=en&lr=&sa=N&tab=ii&oi=imagest

 

No matter what shape, the native element Gold is a beautiful, timeless, precious metal that will continue to be adored and enjoyed by all those who cherish it. 
 

Works Cited

 

Alden, Andrew.  18 Nov. 2005.  http://geology.about.com/cs/mineralogy/a/aa101297.htm

Gagnon, Steve. 18 Nov. 2005. http://education.jlab.org/itselemental/ele079.html

http://en.wikipedia.org/wiki/Gold

http://goldcoinshop.com/history_of_gold.html

http://home.att.net/~desert-gold-diggers/gold/goldfacts.htm

http://pubs.usgs.gov/gip/prospect1/goldgip.html

http://skywalker.cochise.edu/weller/mineral/gold.goldL.htm

http://www.aboutgems.org/Gold.php

http://www.desertusa.com/mag98/june/papr/geo_gold.html

http://www.geotemps.com/goldfacts.html

http://www.gi.alaska.edu/~jesse/treasure/gold/goldfacts.html

http://www.goldcoins.org.html

http://www.historichwy49.com/goldfact.html

http://www.responsiblegold.org/role_of_gold.asp