Minerals are the building blocks rocks blocks of rocks. Some rocks are made up of only one mineral while others contain many of them. Only rarely do useful minerals occur in sufficient concentrations to make commercial exploitation worthwhile [Key]. Increasingly sophisticated technology means, however, that deposits that were uneconomic to work a few years ago can now be profitably exploited. New techniques have also made it possible to re-work the waste heaps of some mines. Scarcity due to an increased demand or to depletion of richer reserves can also make the extraction of low-grade ores profitable without necessarily involving a change of the basic mining techniques being employed.
The economic minerals such as precious stones and the ores of useful metals are those that usually come to mind when minerals are mentioned, but these actually represent a small part of the mineral kingdom. The largest components are the rock-forming minerals, the building blocks rocks blocks from which the earth's crust and all its rocks are constructed. These can be so attractive, with their great variety of crystal shapes and range of colours, that finding and collecting minerals has been a popular hobby for thousands of years.
A glacier is one of the most powerful agents of erosion. Its ice erodes by abrasion and by plucking away at the bedrock. Blocks embedded in the ice are scraped along the bottom, producing grooved (striated) rocks, and resistant rocks are polished into roches moutonnees. The source area is enlarged into an amphitheatre known as a cirque or corrie, and where two such cirques meet they are separated by a sharp ridge called an arete.
Minerals are the building blocks rocks blocks of rocks. Some rocks are made up of only one mineral while others contain many of them. Only rarely do useful minerals occur in sufficient concentrations to make commercial exploitation worthwhile [Key]. Increasingly sophisticated technology means, however, that deposits that were uneconomic to work a few years ago can now be profitably exploited. New techniques have also made it possible to re-work the waste heaps of some mines. Scarcity due to an increased demand or to depletion of richer reserves can also make the extraction of low-grade ores profitable without necessarily involving a change of the basic mining techniques being employed.