Earth’s mineral resources
The Earth’s crust is said to contain 88 elements in concentrations that spread over at least seven orders of magnitude. Some elements are defined as “common,” with concentrations over 0.1% in weight. Of these, five are technologically important in metallic form: iron, aluminum, magnesium, silicon, and titanium. All the other metals exist in lower concentrations, sometimes much lower. Most metals of technological importance are defined as “rare” and exist mostly as low concentration substituents in ordinary rock, that is, dispersed at the atomic level in silicates and other oxides. The average crustal abundance of rare elements, such as copper, zinc, lead and others, is below 0.01% (100 ppm). Some, such as gold, platinum and rhodium, are very rare and exist in the crust as a few parts per billion or even less. However, most rare elements also form specific chemical compounds that can be found at relatively high concentrations in regions called “deposits”. Those deposits from which we actually extract minerals are called “ores”...
