Noticeably heavy and with a bright yellow metallic color, gold is extremely malleable and ductile (deformed plastically without fracture), with a relatively low melting point (1063 degrees Celsius). Due to its extreme malleability, one ounce (28 grams) of pure gold can be beaten out to 300 square feet. Gold is widely used as an international currency standard, and commonly is used for jewelry fabrication and dentistry in part due to its hypoallergenic properties, electronics (due to its superb conduction properties), and in certain photographic processes.
The allure of gold has been documented since the beginning of recorded history, and at least 6,000 years ago was utilized by the ancient civilizations of Egypt and Mesopotamia. Probably initially discovered in stream beds as nuggets or flakes, gold also occurs in primary hydrothermal veins, in ancient and more rarely active volcanoes, and also is found in alluvial sources, also called placer deposits. When gold is found as nuggets, it is rarely found in a completely pure state and often occurs mixed with silver. When the ratio is roughly 75% gold to 25% silver, the material is called Electrum. Gold also may occur in granitic pegmatites or in contact metamorphic deposits. Crystallized gold is very rare, but when found make beautiful aesthetic specimens that are increasingly left as is rather than destroyed for their gold value alone. Forms of gold crystals include rounded octahedra, cubes, and dodecahedra to 2 cm. and often elongated along certain crystallographic planes resulting in herringbone and dendritic twin forms. Gold also occurs in flattened plates with triangular octahedral faces, and rarely as wires. Other forms include massive rounded fragments, flattened grains, and as gold dust.
The word “gold” is derived from the Anglo Saxon word of the same name; in Latin, gold was called aurum, hence the abbreviation “Au” for gold in the periodic table. Gold is very soft in its pure state, and in order to make it more wearable (as well as extending the amount of gold available), it is usually mixed or alloyed with one or more other metals to add stability and keep the gold from literally wearing away by the action of rubbing and hitting. Pure gold is termed 24 Karat (Kt.), meaning out of 24 parts, 24 of those parts are gold. The terms 18 Karat and 14 Karat indicate that 18 parts (75%) or 14 parts (58.3%), respectively, of 24 parts are pure gold. The other six to ten parts generally consist of silver, copper, zinc, and, in the case of colored gold, other metals. More copper mixed with gold results in red or pink gold. Green gold is created by adding more silver. Other gold colors include black, brown, purple and blue. Rarely seen is blue gold, obtained by adding iron to gold. To create white gold, palladium or nickel is added to the recipe, creating a very light yellow gold. To whiten the gold further, the object is then plated with rhodium, a platinum group metal, resulting in the white gold commonly used in jewelry. White gold became popular during World War II, when platinum was unobtainable due to its application in military weapons. Primary sources for gold include South Africa, Russia, Brazil, Australia, Canada and the United States.
Chemical Symbol: Au
Crystal System: Cubic
Specific Gravity: 19.3
Hardness: 2 ½ - 3
Melting Point: 1063 degrees Celsius