Gold.
As one of the rarest elements---the Earth's crust averaging 0.0004 grams of gold per ton---gold is a soft, lustrous yellow substance and considered the most beautiful and precious of all metals. It can be found in alluvial deposits and veins in regions distributed widely over the Earth. Sluicing and panning operations separate gold from rocks and other minerals, while smelting processes recover gold from its ore. Refining is carried out by electrolysis.
Basic Properties
The melting point of gold is 1,064 degrees C, however when it's alloyed with other elements (e.g., silver, copper) the gold alloy will melt over a range of temperatures. The boiling point of gold is 2,860 degrees C.
Chemical Symbol: Au
Atomic number: 79
Atomic weight: 196.97
Relative density: 19.3
Electrical resistivity (RT): 2.20 x 10--8Om
Thermal conductivity: 319Wm--1K--1
Dense and Heavy
In contrast to the density of other materials such as aluminum (2.7 gcm-3) or steel (7.87 gcm-3), gold is very dense (19.3 gcm-3). Whereas a 1-liter carton of milk weighs 1kg, that same liter filled with gold weighs 19kg. It is almost twice the weight of lead and virtually indestructible. In practice, gold can only be corroded by a mixture of nitric and hydrochloric acid (aqua regia).
Malleable and Ductile
Gold is easily hammered into flat sheets as well as drawn out into thin wires. An ounce of gold can be shaped into 50 miles of wire that's only five microns thick. The ancient technique of gilding (also known as gold leafing) involves beating gold between pieces of leather. The resulting gold leaf can be seven-millionths of an inch thick. A stack of over 7,000 sheets would be no thicker than a small coin.
Conductive
Used as a contact metal in the electronics industry, gold transfers heat and electricity. Although silver and copper are more frequently used as conductors, gold does not tarnish, resists corrosion and abrasion, and therefore remains conductive for a longer period time.
Reflective of Light and Heat
Highly reflective of infrared and red wavelengths, gold is used to coat the visors of astronauts' space helmets. Thin to the point of transparency---0.000002 inches---the gold film reduces heat and glare from sunlight.
Biocompatibility
Gold shows a high degree of resistance to bacterial colonization and therefore is the material of choice for implants that risk infection. Its compatibility with the human body has led to wide range of medical applications. For example, gold is frequently used as a dental alloy.
Tags: frequently used, gold degrees, gold from, point gold, point gold degrees