Editing Mineral (section)

==Rocks, ores, and gems==
[[File:Sillimanite-199671.jpg|thumb|upright|[[Schist]] is a [[metamorphic rock]] characterized by an abundance of platy minerals. In this example, the rock has prominent [[sillimanite]] [[porphyroblast]]s as large as {{convert|3|cm|in|abbr=on}}.]]
A [[Rock (geology)|rock]] is an aggregate of one or more minerals<ref name="ChL15-16">{{harvnb|Chesterman|Lowe|2008}}, pp. 15–16</ref> or mineraloids. Some rocks, such as [[limestone]] or [[quartzite]], are composed primarily of one mineral&nbsp;– [[calcite]] or [[aragonite]] in the case of limestone, and [[quartz]] in the latter case.<ref>{{harvnb|Chesterman|Lowe|2008}}, pp. 719–21</ref><ref>{{harvnb|Chesterman|Lowe|2008}}, pp. 747–48</ref> Other rocks can be defined by relative abundances of key (essential) minerals; a [[granite]] is defined by proportions of quartz, [[alkali feldspar]], and [[plagioclase feldspar]].<ref>{{harvnb|Chesterman|Lowe|2008}}, pp. 694–96</ref> The other minerals in the rock are termed ''accessory minerals'', and do not greatly affect the bulk composition of the rock. Rocks can also be composed entirely of non-mineral material; [[coal]] is a sedimentary rock composed primarily of organically derived carbon.<ref name="ChL15-16" /><ref>{{harvnb|Chesterman|Lowe|2008}}, pp. 728–30</ref>

In rocks, some mineral species and groups are much more abundant than others; these are termed the ''rock-forming minerals''. The major examples of these are quartz, the [[feldspar]]s, the [[mica]]s, the [[amphibole]]s, the [[pyroxene]]s, the [[olivine]]s, and calcite; except for the last one, all of these minerals are silicates.<ref>{{harvnb|Dyar|Gunter|2008}}, p. 15</ref> Overall, around 150 minerals are considered particularly important, whether in terms of their abundance or aesthetic value in terms of collecting.<ref name="ChL14">{{harvnb|Chesterman|Lowe|2008}}, p. 14</ref>

Commercially valuable minerals and rocks, other than gemstones, metal ores, or mineral fuels, are referred to as ''[[Industrial mineral|industrial minerals]]''.<ref>{{cite book |editor1-last=Jackson |editor1-first=Julia A. |title=Glossary of geology. |date=1997 |publisher=American Geological Institute |location=Alexandria, Virginia |isbn=0-922152-34-9 |edition=Fourth |chapter=Industrial mineral}}</ref> For example, [[muscovite]], a white mica, can be used for windows (sometimes referred to as isinglass), as a filler, or as an insulator.{{sfn|Nesse|2000|p=246}}

[[Ore]]s are minerals that have a high concentration of a certain element, typically a metal. Examples are [[cinnabar]] (HgS), an ore of mercury; [[sphalerite]] (ZnS), an ore of zinc; [[cassiterite]] (SnO<sub>2</sub>), an ore of tin; and [[colemanite]], an ore of [[boron]].

[[gemstone|''Gems'']] are minerals with an ornamental value, and are distinguished from non-gems by their beauty, durability, and usually, rarity. There are about 20 mineral species that qualify as gem minerals, which constitute about 35 of the most common gemstones. Gem minerals are often present in several varieties, and so one mineral can account for several different gemstones; for example, [[ruby]] and [[sapphire]] are both [[corundum]], Al<sub>2</sub>O<sub>3</sub>.<ref name="ChL14-15">{{harvnb|Chesterman|Lowe|2008}}, pp. 14–15</ref>