5. How are tungsten prices quoted?
A Metric Tonne Unit ("MTU") is equal to ten kilograms per metric tonne and is the standard weight measure of tungsten. Tungsten prices are generally quoted as US dollars per MTU of tungsten trioxide (WO3). Theoretically pure wolframite concentrate can contain 79.3% tungsten metal, but in practice the grade of concentrate products acceptable for sale ranges from about 62% WO3 to about 72% WO3. Saleability of concentrate depends on grade and also the impurities in the concentrate. Tungsten prices are also quoted as US$ per MTU of WO3 in Ammonium Paratungstate ("APT"), which is a downstream secondary product made from wolframite or scheelite concentrates.