By: Marlene Affeld
Since prehistoric man first stumbled upon a nugget, raw gold with its radiant sun yellow coloration and metallic luster has captivated and fascinated mankind. The unique gleam of gold attracts the eye, enabling the seeker to detect the smallest of grains in an aggregate of many other materials. The tiniest flakes are easily detected.
Anthropological excavations of Stone Age burial sites indicate that gold was the first element collected and prized by man. This unique metal, gathered in the form of nuggets, seems to have been highly prized but was not used in practical applications. Rating 2.5 – 3 on Mohs scale of hardness, gold was much too pliable to be hammered into workable tools or weapons. Gold carried little value for prehistoric man except to be admired and treasured for its rare, intrinsic beauty.
Continue Reading Mysterious Gleaming Gold
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About Gold:courtesy Mindat.org
Formula:
Au
As a Commodity:
Gold
Colour:
A rich yellow, paling to whitish-yellow with increasing silver; blue & green in transmitted light (only thinnest folia [gold leaf])
Luster:
Metallic
Hardness:
2½ - 3
Specific Gravity:
15 - 19.3
Crystal System:
Isometric
Member of:
Copper Group
Name:
Gold is one of the first minerals used by prehistoric cultures. The Latin name for this mineral was "aurum" and Jöns Jakob Berzelius used Au to represent the element when he established the current system of chemical symbols. The Old English word "gold" first appeared in written form about 725 and may further have been derived from "gehl" or "jehl". May be derived from Anglo-Saxon "gold" = yellow. (Known to alchemists as Sol.)
Copper Group. Gold-Silver Series and Gold-Palladium Series.
A native element and precious metal, gold has long been prized for its beauty, resistance to chemical attack and workability. As it is found as a native element, has a relatively low melting point (1063 degrees Celsius) and is malleable, it has been used by mankind for thousands of years.
Gold is used as a standard for international currency and is also widely used in jewelry, electronics (where its superb properties as a conductor help offset its tremendous cost), dentistry and in photographic processes.
Gold occurs in significant amounts in three main types of deposits: hydrothermal quartz veins and related deposits in metamorphic and igneous rocks; in volcanic-exhalative sulphide deposits; and in consolidated to unconsolidated placer deposits. It may also occur in contact metamorphic or hypothermal deposits (eg. Skarns), or epithermal deposits such as volcanic fumaroles. It is most commonly found as disseminated grains in quartz veins with pyrite and other sulphides, or as rounded grains, flakes or nuggets in placer deposits in recent to ancient stream and river deposits. Gold is often panned from such deposits by taking advantage of its high density to wash away the lighter sediments from a pan or sluice.
Nuggets are almost exclusively hypogene in origin, forming mostly in veins, but can be somewhat modified in form and chemistry by weathering, erosion, and transport (Hough et al., 2007).
Physical Properties of Gold
Lustre:
Metallic
Transparency:
Opaque
Colour:
Rich yellow, paling to whitish-yellow with increasing silver; blue & green in transmitted light (only thinnest folia [gold leaf])
Streak:
Shining yellow
Hardness:
2½ - 3 on Mohs scale
Hardness:
VHN10=30 - 34 kg/mm2 - Vickers
Hardness Data:
Measured
Tenacity:
Malleable
Cleavage:
None Observed
None
Fracture:
Hackly
Density:
15 - 19.3 g/cm3 (Measured) 19.309 g/cm3 (Calculated)
Comment:
Calculated density at 0° C. Depends on silver content (pure gold is 19.3).
Gold is the most malleable and ductile metal, which makes it very easy to work with. It never tarnishes, and is unaffected by most chemicals. However, it can discolor by exposure to chlorine, bleach, and certain detergents.
Pure Gold lacks resistance to pressure and easily bends. For this reason, Gold jewelry is always alloyed with other metals to increase its toughness and durability. The purity of Gold depends on the percentage of alloyed metal, and this number is measured in karats. The karat measurement determines the percentage of gold to other metals on a scale of 1 to 24, with 24 karats being pure gold. Common karat weights are 22 kt (91.67% gold), 18 kt (75% gold), 14 kt (58.33% gold), and 10 kt (41.67% gold). Pure 24 kt Gold is never used in jewelry as it too flexible and will be bent and mishaped even by minor touches.
Gold In Jewelry:
Courtesy of PointJewels.co.za
Several different metallic elements are alloyed with Gold, and some are used specifically to produce a certain color or tone in the Gold. The main metals alloyed with Gold are copper, silver, palladium, nickel, zinc, and iron. White Gold, which has become very popular in jewelry, is mainly alloyed with nickel and zinc, and occasionally palladium. White Gold resembles the color of Silver, but it is far more resistant to corrosion and will not tarnish like Silver. Rose Gold, which has a slightly reddish tone, is alloyed mostly with copper. Green gold, which appears greenish-yellow, is alloyed with silver, and Blue Gold, which is gold with a whitish-blue tone, is alloyed with iron.
Some gold-colored jewelry is made out of cheaper metals and coated with a very thin layer of Gold. Such jewelry is known as "Gold-plated". Through normal wear, the layer of gold can erode if it is too thin, exposing the underlying metal.
Gold is one of the heaviest substances on earth. When pure, it has a specific gravity of 19.3. The international weight measurement of Gold is the troy ounce. One troy ounce of gold equals 31.1 grams.
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