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The standard gold bar held and traded internationally by central banks and bullion dealers is the Good Delivery bar with a 400 ozt (12.4 kg; 27.4 lb) nominal weight. However, its precise gold content is permitted to vary between 350 ozt (10.9 kg; 24.0 lb) and 430 ozt (13.4 kg; 29.5 lb). The minimum purity required is 99.5% gold.
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Au 5 Al 2 typically forms at 95% of Au and 5% of Al by mass, its melting point is about 575 °C, which is the lowest among the major gold-aluminum intermetallic compounds. AuAl 2 is a brittle bright-purple compound, with a composition of about 78.5% Au and 21.5% Al by mass.
The 1-ounce gold bar is what is used to calculate live gold prices. There is also a troy ounce, which is the unit used when measuring precious metals. With troy ounces, 12 ounces equal one pound.
Rebound hardness, also known as dynamic hardness, measures the height of the "bounce" of a diamond-tipped hammer dropped from a fixed height onto a material. This type of hardness is related to elasticity. The device used to take this measurement is known as a scleroscope. [3]
Mohs hardness kit, containing one specimen of each mineral on the ten-point hardness scale. The Mohs scale (/ m oʊ z / MOHZ) of mineral hardness is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of minerals through the ability of harder material to scratch softer material.
The great expense of refining the metal made the small available quantity of pure aluminium more valuable than gold. [16] Bars of aluminium were exhibited at the Exposition Universelle of 1855 , [ 17 ] and Napoleon III 's most important guests were given aluminium cutlery, while those less worthy dined with mere silver. [ 16 ]
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