Minerals are naturally occurring inorganic substances that normally are crystalline in form and have well-defined chemical compositions. They are usually stable at room temperature and have an ordered atomic arrangement. Found extensively on our planet, the International Mineralogical Association has approved over 4660 different mineral species. Minerals are distinguished into various species on the basis of chemical composition and physical properties including hardness, lustre, fracture, specific gravity etc. Since silicon and oxygen are found abundantly on the crust (in various forms), silicates top the list of naturally occurring minerals. Following is a list of top 10 minerals in naturally occurring form that are found abundantly on our planet earth starting with the least abundant.
Chemically composed of double chain SiO4 tetrahedron lattice linked at the vertices, amphiboles are generally composed of iron ions and/or magnesium. They are dark in colour and are found in dark shades of green, yellow, blue, brown and green. Their chemical and general characteristics are very similar to that of pyroxenes, which is the next in the list. They may occur as constituents of igneous rocks like graphite and may also be found in limestone rocks. Used predominantly in construction industry, they are harder than limestone and heavier than granite.
Next in the list come pyroxenes which are of igneous or metamorphic rock origin, and are elementally composed of calcium sodium iron, magnesium, zinc and chromium. As discussed earlier, their characteristics largely match those of amphiboles. They are often found as embedded crystals in volcanic glass which may often seem like impurities and occur as green to black-green crystals. With Augite being the most common type of pyroxene, other types like jadeite and spodumene find usage in the ornament industry and glass industry respectively.
Haematite is the naturally occurring mineral form of iron (III) oxide and has a rhombohedral lattice. The mineral appears as black, silvery grey, brown or as a reddish brown ore, has a rusty streak and is the main ore from which iron is derived. Found usually in rocks of sedimentary origin, it may also be found as layers at the bottom of water bodies or as a result of volcanic activity. Historic uses of haematite included those of jewellery & statue making while other uses of iron derived from it are extensive. haematite has ferromagnetic properties, and is often considered to medically active.
Chemically identified as iron (III) oxide, magnetite can act as a natural magnet (lodestone) which is responsible for its specific name. Magnetite grains occur in various igneous and metamorphic rocks and are brownish-black in colour with a metallic lustre. Magnetite grains are often found in beach sands as a result of post-erosion deposits of sedimentary rocks by rivers and also as huge ‘banded iron formations’ of sedimentary rocks. Applications include usage of oxide in magnetic storage, as a catalyst, as boiler coatings and for removing arsenic from impure water among others.
Next in the list comes calcite, a mineral which is unstable at high temperatures and hence is found majorly in earth’s crust and not core. Calcite in the form of calcium carbonate is the most stable polymorph and is responsible for most of earth’s carbon dioxide occurrence. Calcite occurs abundantly in limestone and in metamorphic marbles. The crystals appear as rhombohedral lattices and may be transparent or opaque with a hint of florescence. Multi-coloured in nature, the mineral can be white, red, green, blue or even colourless. Calcite finds usage in soil stabilization, concrete repair and as limestone which has varied usage.
Biotite, a member of the mica group, is basically silicate sheets consisting of iron, magnesium, aluminium, silicon and hydrogen elements which are bound by potassium ions. Commonly known as the ‘iron mica’ or ‘black mica’ because of its high iron content and black colour, it has a pseud-hexagonal lattice. Biottie is infamous for it being considered as gold (fool’s gold) by amateur gold miners due to its golden reflection when hit by sunlight. It is found extensively in igneous and metamorphic rocks and also in volcanic lavas. Biotite has readily escaping argon gas from its lattice and is hence useful for determining age of rocks and assessing their thermal properties.
Muscovite, another member of the mica family is commonly known as ‘white mica’ or ‘potash mica’ and is made up of potassium and aluminium. A multi-coloured transparent/translucent mineral, it may appear in green, yellow, red colour or even colourless. It is the most common form of mica and is found in granite, pegmatite and schist rocks. Anciently it was used as a substitute to glass and as a glittering agent. It is often found in form of huge sheets which have commercial value as fireproofing, insulating and lubricating agent.
The most copious mineral in the earth’s mantle is olivine-a magnesium iron silicate, but when it comes to considering the continental and oceanic crust, it emerges as second runners-up. The dense interior rock upon which the crust floats consists majorly of olivine rocks and it also occurs as a major component of volcanic lavas. Olivine occurs in olive-green colour (hence the name) but may often appear as reddish due to prolonged oxidation. olivine in transparent form is used as a gemstone termed ‘peridot’ and finds application in aluminium industry, as sauna stones and in commercial production of carbon dioxide.
Making it to the 2nd position in the list is Quartz. Quartz is the most abundant and common mineral found on earth’s ‘continental crust’. It is present almost everywhere in form of sand be it deserts, beaches, river beds or sandstones. It is the most common mineral found in granite and gneiss rocks which are found abundantly in earth’s crust. Quartz is found in many variants of which many are semi-precious gemstones and find application in the jewellery industry. In pure form, it is transparent/ translucent and is often used for hard-stone cravings whereas the coloured variants come in rosy, milky, pale yellow and brown colour. The mineral is hard and chemically inert and finds applications in foundries, electrical & heat resistance equipment and in the glass industry.
Topping the charts is feldspar, which if considered a single mineral, is the most common mineral found on earth when both continental and oceanic crust are considered together. The rocks on seafloor and oceanic crust almost always have feldspar but no quartz, making it a clear winner. The name however is for a group of 7 feldspar minerals which are so similar that their properties seamlessly merge into each other. Feldspar is white or nearly white in colour with occasional shades of orange and has a glassy lustre. Chemically speaking, the mineral is majorly composed of silicon and aluminium with presence of elements like potassium, calcium and zinc. Feldspar finds usage in glass-making &ceramics, in fertilizer industry and as a filler in paint, plastic and rubber industry.