The list of commodities is extensive, although the relative proportions mined underground and on the surface vary from mineral to mineral. Massive tonnages of hard coal and lignite are also produced from surface mines, although the terminology used – open cast or open cut, rather than open-pit – indicates that the technology and engineering concepts used are often markedly different from those employed in the hard rock environment.
Open-pit mining differs from quarrying (with the possible exception of iron ore) in that the valuable mineral constitutes only a small proportion of the total tonnage of rock produced. In quarrying, the rock itself is the valuable commodity, with virtually all of the raw rock that is won being processed (often only by crushing and screening) to give saleable products. In open-pit mining, on the other hand, the metal content of the ore produced may be only fractions of a percent, meaning that a huge proportion of the rock produced is effectively waste material.
In addition, the ore body geometry may mean that large tonnages of barren rock also have to be mined and transported in order to access the ore in which the valuable mineral (or minerals) makes up only a small proportion. This has to be recovered from the rock matrix through both physical (crushing and grinding) and/or chemical processes such as flotation, meaning that processing costs are higher. This is reflected in metal commodity prices, with a ton of copper or zinc being valued much more highly than a ton of granite or basalt.