The forces of weather on the surface of the Earth can change the minerals that make up rocks. When mechanical weathering processes destroy old rocks, softer silicate minerals such as olivine and plagioclase may dissolve away, leaving behind harder minerals, such as quartz. In chemical weathering, the atoms react with oxygen or water in the environment. (Think of iron exposed for several months to the water and air outdoors. The iron rusts, and rusting is a kind of chemical weathering.) In the presence of water, some minerals transform into more hydrous minerals. Other minerals, such as calcite (calcium carbonate), dissolve completely in water over time. Some silicate minerals, such as quartz and garnet, are more resistant to weathering than other silicates, such as feldspar and mica.

Pseudomorphs are minerals that have been chemically altered, so that they are new minerals that retain the shape of the original mineral. (The word "pseudomorphic" means "false form" in Greek.) Changes in a mineral's environment can cause the replacement of one mineral with another, atom by atom. In one example, limonite, a type of iron oxide hydroxide, substitutes itself in for pyrite, or iron sulfide, but the crystals are still shaped like the original pyrite. Geologists call the resulting mineral "limonite after pyrite." Another example of pseudomorphism occurs when quartz replaces crocidolite, a variety of riebeckite that is a source of asbestos fibers. The resulting solid mineral retains a fibrous internal structure that gives the stone a particular sheen known as chatoyancy, or the "cat's eye" effect.

Through ancient times and the Middle Ages smelting techniques did not change much and improvements were made by using different techniques to forge the steel. The disadvantage was that every object made of iron or steel had to be made one at a time by a blacksmith. Unlike copper and other metals, furnaces could not get hot enough to melt iron so that it could be cast into molds. About 300 years ago, Europeans developed a more efficient blast furnace that used coal instead of wood charcoal to produce cast iron. Being able to cast iron meant that iron and steel products could be mass-produced; this development eventually gave rise to the Industrial Revolution. Today's industries depend on steel, which is an alloy, or solid mixture, of iron with carbon, manganese, and other trace elements. This combination gives the metal additional strength and reduce iron's tendency to rust, or to bond with oxygen in the atmosphere. Another industrially important metal, aluminum, comes from the ore known as bauxite, a mixture of three aluminum oxide minerals. Until the 1880s, when humans learned how to separate the aluminum and oxygen atoms by running electricity through the aluminum oxide, metallic aluminum was extremely difficult to make, and thus more expensive than gold.