Rocks
CITE
We have made every effort to follow citation style rules, but there may be some minor differences. If in doubt, please refer to the appropriate citation style manual.
Minerals. (2023). In Q-files Encyclopedia, Earth, Rocks. Retrieved from
https://www.q-files.com/earth/rocks/minerals
"Minerals." Earth, Rocks, Q-files Encyclopedia, 11 May. 2023.
https://www.q-files.com/earth/rocks/minerals.
Accessed 19 Mar. 2024.
Minerals 2023. Earth, Rocks. Retrieved 19 March 2024, from
https://www.q-files.com/earth/rocks/minerals
Earth, Rocks, s.v. "Minerals," accessed March 19, 2024.
https://www.q-files.com/earth/rocks/minerals
Minerals
Minerals are naturally-occurring, solid, inorganic (non-living) substances that consist of chemical elements, such as silicon, oxygen, magnesium and others. Various combinations of minerals make up different types of rocks. For example, the rock sandstone consists mainly of grains of sand pressed and cemented together. Sand is made mainly of the minerals quartz and feldspar. Quartz consists of the chemical elements silicon and oxygen; feldspar is composed of a variety of elements. There are thousands of different minerals, each distinguished by their various chemical and physical properties. A very few kinds—feldspar, mica and quartz, for example—are found in nearly all the Earth’s rocks.
Amphibole
The amphiboles are a group of silicate minerals, formed from chains of silicon and oxygen atoms, plus a combination of iron, magnesium, sodium, calcium or aluminium. These minerals usually form long, slender, dark-coloured crystals. Amphiboles are found in igneous and metamorphic rocks. A common amphibole is hornblende. Four of the amphibole minerals are commonly called asbestos.
Apatite
The apatites are a group of phosphate minerals that are compounds of phosphorus and calcium plus elements such as fluorine, chlorine or carbon. Apatite crystals are often green, transparent and hexagonal. These minerals are commonly used for making phosphate fertilizers.
Aragonite
Aragonite is a carbonate mineral, one of the two most common crystal forms of calcium carbonate (the other is calcite). Aragonite is found in sediments, sedimentary rocks and stalactites in limestone caves, as well as in mollusc shells and pearls.
Calcite
Calcite is a carbonate mineral. Along with aragonite, it is one of the two most common crystal forms of calcium carbonate. Calcite forms the majority of the shells of sea creatures, so it is found in large quantities in sedimentary rocks such as limestone (formed from the remains of shells).
Clay minerals
Clay minerals commonly form near the Earth’s surface—they are found particularly in clay and shale. They form in water, where the water has interacted with other minerals and organic matter. All clay minerals are hydrous (contain water) and are compounds of aluminium and silicon, often along with other metals. Common clay minerals include kaolinite, illite and montmorillonite.
Corundum
Corundum is a crystal form of aluminium oxide. Pure corundum is transparent and colourless, but impurities can give it colours: it is called ruby when red (caused by chromium) and sapphire when it has shades of blue (iron), yellow (titanium) or green (magnesium). It is found in both igneous and metamorphic rocks.
Dolomite
Dolomite is a carbonate mineral, composed of calcium, magnesium and carbon. It is found in lakes, shallow oceans and lagoons. Crystals are normally white, grey or pink.
Evaporite
Evaporite minerals are minerals that result from the evaporation of water. They are often found in shallow bodies of water in very dry regions, such as desert lakes. Evaporite minerals include anhydrite, calcite, dolomite and gypsum.
Feldspar
Feldspars are a group of very common rock-forming minerals, found in igneous, sedimentary and metamorphic rocks. They are compounds of aluminium, silicon and oxygen, plus potassium, sodium, calcium or barium. Feldspar minerals are usually white, pink, grey or brown. Feldspars are used in glass-making and ceramics.
Fluorite
Fluorite is the crystal form of calcium fluoride. It is very common in the Earth’s crust. It forms transparent crystals, but impurities can give it a range of colours. The mineral is used as a source of fluorine and fluoride.
Galena
Galena is the crystal form of lead sulphide. It is the most important source of lead, which is easy to extract by melting. It has a bluish-grey to black, metallic appearance. It can be found in sedimentary, igneous and metamorphic rocks.
Garnet
Garnets are a group of silicate minerals, composed of compounds of silicon and oxygen with aluminium or calcium. Garnets are commonly found embedded in igneous and metamorphic rocks. Used both as gemstones and abrasives (for rubbing and polishing), they are often red but may occur in a range of colours.
Gypsum
Gypsum is composed of calcium, sulphur, oxygen and water. It is widely mined for use in plaster and fertilizer. A white form of gypsum is called alabaster, which is carved to make sculptures.
Haematite
Haematite is composed of iron oxide (a compound of iron and oxygen). It is commonly mined to extract iron. Haematite often forms in the presence of water, as in a hot spring. The crystals vary from black to red, but all forms will leave a rust-red streak if scraped over white pottery.
Magnetite
Magnetite is composed of iron oxide (a compound of iron and oxygen). It is the most magnetic of all natural minerals. Once called lodestone, the mineral was used in the earliest magnetic compasses. Magnetite grains are common in igneous and metamorphic rocks.
Mica
Micas are a group of silicate minerals, composed of compounds of silicon, oxygen and aluminium, often with potassium, iron, magnesium or lithium. They all share the characteristic of splitting easily into thin, tough sheets. They are commonly used as electrical insulators. Micas are widespread in igneous, sedimentary and metamorphic rocks. A common mica is biotite.
Olivine
The olivines are a group of magnesium iron silicates (compounds of magnesium, iron, silicon and oxygen). Gem-quality olivine is called peridot, which is a green semi-precious stone. Olivines are common in igneous rocks rich in magnesium and iron, including basalt and gabbro.
Pyrite
Pyrite is a compound of iron and sulphur. It is often called “fool’s gold” because its shiny, yellowish appearance makes it look like gold. Pyrite is widely used for industrial purposes, from the production of sulphuric acid to semiconductors. It is common in the Earth’s crust.
Pyroxene
Pyroxenes are a group of silicate minerals, formed from chains of silicon and oxygen atoms, plus elements such as magnesium, iron and calcium. Pyroxenes are important rock-forming minerals, particularly common in igneous and metamorphic rocks.
Quartz
Quartz is composed of silicon and oxygen (silicon dioxide). Most quartz crystallizes from molten magma. Pure quartz is colourless and transparent, but impurities give it colours such as purple (called amethyst), reddish-orange (carnelian) and multi-coloured bands (agate). When placed in an electric field, pure quartz oscillates (vibrates) at a constant frequency, so it is useful for controlling precise devices such as watches.
Rutile
Rutile is composed of titanium and oxygen (titanium dioxide). Rutile has a great number of uses, from white paint pigment to sunscreens. It is very common in metamorphic and igneous rocks.
Serpentine
The serpentine minerals are a group of silicate minerals, containing iron and magnesium. Many types of serpentine have been used for jewellery and stone carving. One serpentine mineral, chrysotile, which is made up of thin, white crystalline fibres, is a common type of asbestos. Until it was discovered that its fibres caused cancer, asbestos was widely used in panels for roofs, ceilings and walls and floors, as well as brake linings, fire barriers and pipe insulation.
Silicate
Silicate minerals are compounds of silicon and oxygen, often in combination with other elements. They are the largest group of rock-forming minerals and compose about 90% of the Earth’s crust. The most common silicate minerals include: amphiboles, clay minerals, feldspars, garnets, micas, olivines, pyroxenes, quartz, serpentines, talc, topaz and zircon.
Talc
The mineral talc is composed of magnesium, silicon, oxygen and water. In powdered form, it is widely used as talcum powder. It is the softest known mineral. Talc is often formed when minerals containing magnesium (such as pyroxenes, amphiboles and olivines) are subjected to intense heat and pressure in the presence of carbon dioxide and water.
Topaz
Topaz is a silicate mineral, composed of silicon, oxygen, fluorine and aluminium. It is valued as a gemstone. Pure topaz is colourless and transparent, but is given a range of colours by impurities. Topaz is often found in cavities in igneous rocks.
Zircon
Zircon is a silicate mineral, composed of silicon, oxygen and the metal zirconium. Colourless zircon is sometimes substituted for diamonds in jewellery, but other colours include blue, brown, yellow and green. Small zircon crystals and grains are common in igneous, metamorphic and sedimentary rocks.
Consultant: Ian Fairchild