Troy ounces, carats and TREO

Precious metals are weighed in troy ounces: 31.1035 grams. A kilogram bar holds about 32.15 troy ounces.

Fineness is purity in parts per thousand (999.9 is 'four nines' gold). Karat describes jewellery gold: 24 karat is pure, 18 karat is 75% gold.

Gemstones are weighed in carats: 0.2 grams each. Price per carat usually rises steeply with size, so a 2-carat stone is worth far more than two 1-carat stones.

Rare-earth concentrates are valued on their Total Rare-Earth Oxide content, a percentage, and on the mix of individual elements within it.