The milestone was hit Friday after the precious metal’s spot price surpassed $2,500 per troy ounce. Gold bars typically weigh 400 troy ounces, so a standard gold bar is valued at a million dollars.

London and New York are the world¡¯s main gold trading centers. In London, gold is typically traded in 400-troy ounce bars, weighing about 12.5 kg. In New York, however, the standard is a 1 kg bar, ...