Gold is the most malleable and ductile metal; a single gram can be beaten into a sheet of one square meter, or an ounce into 300 square feet. Gold leaf can be beaten thin enough to become translucent. The transmitted light appears greenish blue, because gold strongly reflects yellow and red.Gold readily forms alloys with many other metals. These alloys can be produced to increase the hardness or to create exotic colors (see below). Gold is a good conductor of heat and electricity, and is not affected by air and most reagents. Heat, moisture, oxygen, and most corrosive agents have very little chemical effect on gold, making it well-suited for use in coins and jewelry; conversely, halogens will chemically alter gold, and aqua regia dissolves it via formation of the chloraurate ion.
Common oxidation states of gold include +1 (gold(I) or aurous compounds) and +3 (gold(III) or auric compounds). Gold ions in solution are readily reduced and precipitated out as gold metal by adding any other metal as the reducing agent. The added metal is oxidized and dissolves allowing the gold to be displaced from solution and be recovered as a solid precipitate.
Recent research undertaken by Sir Frank Reith of the Australian National University shows that microbes play an important role in forming gold deposits, transporting and precipitating gold to form grains and nuggets that collect in alluvial deposits.[1]
High quality pure metallic gold is tasteless, in keeping with its resistance to corrosion (it is metal ions which confer taste to metals).
In addition, gold is very dense, a cubic meter weighing 19300 kg. By comparison, the density of lead is 11340 kg/m³, and the densest element, iridium, is 22650 kg/m³.
Colour of gold
The usual gray colour of metals depends on their "electron sea" that is capable of absorbing and re-emitting photons over a wide range of frequences. Gold behaves differently, depending on subtle relativistic effects that affect the orbitals around gold atoms.
Malleability occurs as a result of the specific type of bond found in metals (Main article: metallic bond). In metallic bonds, valence shell electrons are delocalized and shared between many atoms. This is often referred to as the "sea of electrons" and is responsible for many properties of metal. The delocalized electrons allow metal atoms to slide past one another without being subjected to strong repulsive forces that would cause other materials to shatter.
Gold is the most malleable metal, followed by aluminium. Many plastics, and amorphous solids such as Play-Doh are also malleable.
It also means changeable, as in "we are all malleable".
Ductility is a mechanical property which describes how much plastic deformation a material can sustain before fracture occurs. Examples of highly ductile metals are silver, gold, copper, and aluminium. The ductility of steel varies depending on the alloying constituents. Increasing levels of carbon decreases ductility, i.e. the steel becomes more brittle.
Ductility can be quantified by the fracture strain, which is the strain at which a test specimen breaks during a uniaxial tensile test. Another commonly used measure is the reduction of area at fracture.
The brittle-ductile transition zone is the strongest part of the Earth's crust. For quartz and feldspar rich rocks in continental crust this occurs at an approximate depth of 10-15 km (equivalent to temperatures in the range 350-450°C). At this depth rock becomes less likely to fracture, and more likely to deform ductilely by creep. This happens because the brittle strength of a material is increased by the confining pressure, whilst the ductile strength of a material decreases with increasing temperature. The transition zone occurs at the level in the crust where the downwards increasing brittle strength equals the upwards inreasing ductile strength, giving a characteristic "saw-tooth" crustal strength profile. This zone is, therefore, the strongest part of the crust and the depth at which many earthquakes occur. The level of the transition zone depends on both strain rate and temperature gradient, being shallower for slow deformation and/or high heat flow and deeper for fast deformation and/or low heat flow. Crustal composition will also affect the depth at which this zone occurs.
It is a common misunderstanding that the BDTZ is caused by rock becoming "soft" in the higher temperature of the deep. This is false. Deep rock does not become soft; on the contrary, it becomes harder, more like steel (or prestressed concrete) and less likely to crack under pressure.
Malleability
Malleability is a mechanical property of matter, but is most commonly used in reference to metals and metalloids. A malleable metal is capable of being extended, shaped, or otherwise deformed without cracking by the processes of hammering or rolling. This property is important in metalworking, as materials that crack or break under pressure cannot be hammered or rolled. Malleable materials can be formed using stamping or pressing, whereas brittle metals and plastics must be molded.Malleability occurs as a result of the specific type of bond found in metals (Main article: metallic bond). In metallic bonds, valence shell electrons are delocalized and shared between many atoms. This is often referred to as the "sea of electrons" and is responsible for many properties of metal. The delocalized electrons allow metal atoms to slide past one another without being subjected to strong repulsive forces that would cause other materials to shatter.
Gold is the most malleable metal, followed by aluminium. Many plastics, and amorphous solids such as Play-Doh are also malleable.
It also means changeable, as in "we are all malleable".
Ductility
Ductility is a mechanical property which describes how much plastic deformation a material can sustain before fracture occurs. Examples of highly ductile metals are silver, gold, copper, and aluminium. The ductility of steel varies depending on the alloying constituents. Increasing levels of carbon decreases ductility, i.e. the steel becomes more brittle.Ductility can be quantified by the fracture strain, which is the strain at which a test specimen breaks during a uniaxial tensile test. Another commonly used measure is the reduction of area at fracture.
The brittle-ductile transition zone is the strongest part of the Earth's crust. For quartz and feldspar rich rocks in continental crust this occurs at an approximate depth of 10-15 km (equivalent to temperatures in the range 350-450°C). At this depth rock becomes less likely to fracture, and more likely to deform ductilely by creep. This happens because the brittle strength of a material is increased by the confining pressure, whilst the ductile strength of a material decreases with increasing temperature. The transition zone occurs at the level in the crust where the downwards increasing brittle strength equals the upwards inreasing ductile strength, giving a characteristic "saw-tooth" crustal strength profile. This zone is, therefore, the strongest part of the crust and the depth at which many earthquakes occur. The level of the transition zone depends on both strain rate and temperature gradient, being shallower for slow deformation and/or high heat flow and deeper for fast deformation and/or low heat flow. Crustal composition will also affect the depth at which this zone occurs.
It is a common misunderstanding that the BDTZ is caused by rock becoming "soft" in the higher temperature of the deep. This is false. Deep rock does not become soft; on the contrary, it becomes harder, more like steel (or prestressed concrete) and less likely to crack under pressure.
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