A precious metal is a rare, naturally occurring metallic chemical element of high economic value. Chemically, the precious metals are less reactive than most elements. They are usually ductile and have a high lustre. Historically, precious metals were important as currency but are now regarded mainly as investment and industrial commodities. Gold, silver, platinum, and palladium each have an ISO 4217 currency code.
The best-known precious metals are the coinage metals, gold and silver. While both have industrial uses, they are better known for their uses in art, jewellery and coinage. Other precious metals include the platinum group metals: ruthenium, rhodium, palladium, osmium, iridium, and platinum, of which platinum is the most widely traded.
Silver coins are possibly the oldest mass-produced form of coinage. Silver has been used as a coinage metal since the times of the Greeks; their silver drachmas were popular trade coins. The ancient Persians used silver coins between 612-330 BC. Before 1797, British pennies were made of silver.
As with all collectible coins, many factors determine the value of a silver coin, such as its rarity, demand, condition and the number originally minted. Ancient silver coins coveted by collectors include the Denarius and Miliarense, while more recent collectible silver coins include the Morgan Dollar and the Spanish Milled Dollar.
The troy ounce (oz t) is a unit of imperial measure. In the present day it is most commonly used to gauge the mass of precious metals. One troy ounce is currently defined as exactly 0.0311034768 kg or 31.1034768 g. There are approximately 32.15 troy oz in 1 kg. One troy ounce is equivalent to approximately 1.09714 avoirdupois ounces.
The troy ounce is part of the troy weights system, many aspects of which were indirectly derived from the Roman monetary system. The Romans used bronze bars of varying weights as currency. An aes grave weighed equal to 1 pound. One twelfth of an aes grave was called an uncia, or in English an "ounce". Later standardization would change the ounce to 1/16 of a pound (the avoirdupois ounce), but the troy ounce, which is 1/12 of a troy pound (note that a troy pound is lighter than an avoirdupois pound), has been retained for the measure of precious metals. At 480 grains, the troy ounce is heavier than the avoirdupois ounce, which weighs 437.5 grains. Since the implementation of the international yard and pound agreement of 1959, a grain has been defined as exactly 64.79891 milligrams (mg); hence one troy ounce is 31.1034768 grams (g) (exact by definition), about 10 percent more than the avoirdupois ounce, which is 28.349523125 g (exact).
Troy weight is a system of units of mass customarily used for precious metals and gemstones. There are 12 troy ounces per troy pound, rather than the 16 ounces per pound found in the more common avoirdupois system. The troy ounce is 480 grains, compared with the avoirdupois ounce, which is 437½ grains. Both systems use the same grain defined by the international yard and pound agreement of 1959 as exactly 0.06479891 gram. Although troy ounces are still used to weigh gold, silver, and gemstones, troy weight is no longer used in most other applications.
The United States dollar (sign: $; code: USD; also abbreviated US$), is referred to as the U.S. dollar or American dollar. It is the official currency of the United States and its overseas territories. It is divided into 100 smaller units called cents.
Junk silver is an informal term used in the United States, United Kingdom, Canada and Australia for any silver coin which is in fair condition and has no numismatic or collectible value above the bullion value of the silver it contains. Such coins are popular among people seeking to invest in silver, particularly in small amounts. The word "junk" refers only to the value of the coins as collectibles and not to the actual condition of the coins; junk silver is not necessarily scrap silver.
Precious metals including silver are measured in troy ounces (ozt). A spot price for silver is the price for a troy ounce of silver which is 99.9-percent pure, or 999 fine. Silver coins including junk-silver coins have set silver-alloy contents ranging from 35-percent to 90-percent or more. The term "coin silver," for example, refers to 90-percent silver alloy which was the most common alloy used to mint silver U.S. coins.
In physics, mass (from Greek μᾶζα "barley cake, lump [of dough]") is a property of a physical system or body, giving rise to the phenomena of the body's resistance to being accelerated by a force and the strength of its mutual gravitational attraction with other bodies. Instruments such as mass balances or scales use those phenomena to measure mass. The SI unit of mass is the kilogram (kg).
For everyday objects and energies well-described by Newtonian physics, mass has also been said to represent an amount of matter, but this view breaks down, for example, at very high speeds or for subatomic particles. Holding true more generally, any body having mass has an equivalent amount of energy, and all forms of energy resist acceleration by a force and have gravitational attraction; the term matter has no universally-agreed definition under this modern view.