COAL, PETROLEUM and amber lack a definite chemical composition and an orderly atomic structure; they are not minerals, although they are referred to as MINERAL RESOURCES. Pearls, CORAL and shells are composed of crystalline calcium carbonate and are referred to as biogenic minerals because they were formed by living organisms. Laboratory grown (synthetic) compounds are not minerals, although their chemistry and structure may be identical to naturally occurring minerals. There are about 3000 known mineral species; about 80 new species are discovered yearly.
To establish a new species, all data relating to the mineral, including its chemical, structural, physical and optical properties, must be approved by the Commission on New Minerals and New Mineral Names of the International Mineralogical Association. The association also judges the acceptability of the proposed name. Minerals are named in various ways, some in honour of a person ( weloganite, after Sir William E. LOGAN), a locality (athabascaite), an institution (mcgillite), the chemical composition (cobaltite), or a distinctive property such as colour (azurite) or shape (cylindrite).
Many names are derived from Latin or Greek words describing characteristic features, eg, albite [Lat albus, "white"] or rhodonite [Gk rhodon, "rose"]. All accumulated scientific data concerning the newly named mineral are published in a recognized international journal, such as the Canadian Mineralogist, for dissemination worldwide.
Minerals occur as components of rocks and, less commonly, as concentrations in rocks. Individual minerals may be readily recognized in coarse-textured rocks (eg, granite) but not in fine-grained rocks (eg, lava, shale). Concentrations of minerals range from small occurrences to large deposits and are formed by various processes, including solidification of mineral-bearing solutions in rock openings (eg, fissures, cavities), precipitation from mineral-rich waters as in springs and saline lakes, and solidification of gases during volcanic eruptions. In each case, minerals grow when appropriate temperature and pressure allow atoms in magma (molten rock), solutions or gases to group together into the basic, mineral-forming building blocks.
Structurally, minerals are grouped into 7 crystal systems, each giving rise to characteristic geometrical shapes. These systems - cubic (isometric), tetragonal, hexagonal, trigonal, orthorhombic, monoclinic and triclinic - are derived from 7 basic boxlike forms, each made up of atoms arranged in a precise and orderly fashion. During crystal growth, these basic building blocks align themselves symmetrically in 3 directions to produce a crystalline solid. If there is sufficient space during growth, a crystal with smooth geometrical faces, reflecting its internal structure, may form; usually, growth conditions are not ideal and minerals form as masses of generally microscopic crystals or in other aggregates (fibrous, powdery, flaky, globular, etc).
Minerals are defined and identified on the basis of their chemical composition and structure. A chemical analysis may range from a test for the presence of one or a few elements to a complete quantitative analysis. The techniques may be simple (eg, a flame test) or may involve sophisticated instruments (eg, electron microprobe, optical spectrograph). Minerals may, however, be identified without use of elaborate laboratory equipment. The most noticeable properties are those influencing appearance.ASBESTOS), lamellar or scaly (MICA), platy (BARITE) or globular (hematite). Crystal forms, such as cubes and octahedra (fluorite and magnetite), rhombs (calcite) and 6-sided prisms (quartz and beryl) may also be readily recognized. COPPER, chalcopyrite), may be diagnostic. Other minerals (eg, spinel, fluorite, corundum) may occur in various colours. Colour in minerals results from atoms or structural defects (colour centres) that absorb certain portions of the spectrum of light; the unabsorbed portion is reflected or transmitted to the eye as colour. The colour of the powdered mineral (its streak) is more reliable than that of the intact mineral. The streak is produced by rubbing the mineral across an unglazed porcelain plate. Yellow, brown or black sphalerite has a cream-white streak; black or reddish brown hematite has a dark red streak. Some minerals produce a fluorescent colour when exposed to ultraviolet light, eg, the white, TUNGSTEN-ore mineral scheelite fluoresces bluish white, a property used in PROSPECTING for it. Minerals that continue to fluoresce after the ultraviolet light source has been removed are referred to as phosphorescent.
Lustre, the reflection of light from mineral surfaces, is classified as metallic or nonmetallic. Various terms are used to describe nonmetallic lustre, including vitreous (glassy), adamantine (brilliant), resinous, waxy or oily, silky, pearly and earthy (dull). Lustre is generally more characteristic of a particular mineral than colour.
Specific gravity is the density or weight of a substance, compared to the weight of an equal volume of water (specific gravity, 1). Galena, an ore of lead, has a density of 7.5, ie, it is 7.5 times heavier than water. The atomic weight of elements forming the mineral and the packing arrangement (ie, whether atoms are close or far apart) affect specific gravity. In stream gravels, minerals are separated by their specific gravity, heavier ones settling to the bottom.
Optical properties refer to the behaviour of light passing through a mineral. Light travels more slowly in minerals than in air and the amount of slowing varies from mineral to mineral. With the loss of speed, light changes its path, or is refracted. The degree of slowing, referred to as the index of refraction, may be expressed as the ratio of the speed of light in air to the speed in a given mineral. For example, light travels at 299 330 km per second (km/s) in air (refractive index 1) but slows down to 123 916 km/s in diamond (ie, light travels 2.41 times as fast in air); hence the refractive index of diamond is 2.41.
All minerals, except those in the cubic (isometric) system, bisect an incoming light ray when it travels along certain crystallographic directions. Each ray is slowed down to a different degree; hence, each ray will have its own index of refraction and the mineral will have 2 indices of refraction along certain directions. Such minerals are referred to as optically anisotropic; minerals with only one refractive index are described as isotropic. To determine the refractive index, mineralogists use the petrographic (polarizing) microscope; gemologists, the refractometer.
A sulphide mineral is composed of sulphur with one or more metallic elements (eg, galena, chalcopyrite) or sulphur with a semimetallic element (realgar). A sulphosalt, or double sulphide, is composed of sulphur with both metallic and semimetallic elements (pyrargyrite). Sulphides and sulphosalts are generally opaque, have metallic lustre and a hardness of 1-6, and occur commonly in veins. They include the important ore minerals.
Oxide minerals are composed of oxygen with one or more metals or semimetals (eg, hematite). If hydrogen is also present, as in goethite, the mineral is classed as a hydroxide. Oxides generally have simple chemistry and structure.
Halides are minerals composed of the halogen elements (fluorine, chlorine, bromine, iodine) with a metal (eg, halite or table salt, fluorite). Halides are generally soft, brittle and light in colour; some are water soluble. The halides form an important group of industrial minerals, including halite, sylvite (a source of potash), chlorargyrite (ore of silver) and fluorite.
Carbonates, Nitrates, Borates
Minerals in these classes have the same basic structural unit (ie, a radical) consisting of 3 oxygen atoms arranged in an equilateral triangle. In each class, a different type of atom is positioned in the centre of the triangle: the centre position in carbonates is occupied by a carbon atom and the radical is CO3; in nitrates by nitrogen (radical NO3); in borates by boron (radical BO3). Each triangular unit is held to similar ones by atoms of metallic elements. Carbonate minerals are most common; calcite and dolomite are the major constituents of LIMESTONE and marble. Carbonates are generally soft and soluble in acids; nitrates are water soluble and occur only in arid regions.
Sulphates, Phosphates, Chromates, Arsenates, Vanadates
Minerals in these classes have the same type of basic building block (radical), a tetrahedron (pyramid shape) with one oxygen atom at each of its 4 corners and an atom characteristic of the class inside. In sulphates the inner atom is sulphur and the radical is SO4; the others are phosphorus in phosphates (PO4), CHROMIUM in chromates (CrO4), arsenic in arsenates (AsO4) and vanadium in vanadates (VO4). Atoms of metallic elements unite the tetrahedra to form minerals. Barite and gypsum are important sulphates; apatite is an important phosphate.
The radical in minerals in these classes is the tetrahedron of 4 oxygen atoms surrounding an atom of MOLYBDENUM in molybdates (MoO4) or tungsten in tungstates (WO4). These tetrahedra are distorted by the large atoms inside.
Silicates are minerals containing silicon and oxygen; they make up over 90% of the Earth's crust and about one-quarter of known mineral species (see SILICA). The basic building block of silicates is the silicon-oxygen tetrahedron (SiO4). The silicates are classified into 6 groups according to ways in which the tetrahedra are joined to each other: in neosilicates, the basic tetrahedra are held together by atoms of other elements (eg, zirconium in zircon); in sorosilicates, pairs of tetrahedra share one corner atom and the "bow tie" shaped units formed are held together by atoms of other elements (eg, hemimorphite); in cyclosilicates, which have a ring structure, each tetrahedron shares a corner oxygen atom with the 2 adjoining tetrahedra (eg, beryl); in inosilicates, which have a chain structure, each tetrahedron shares an oxygen atom with the 2 adjoining tetrahedra and the chains are aligned and joined by atoms of other elements (eg, pyroxene); in phyllosilicates, which have a sheet structure, each tetrahedron shares 3 oxygen atoms with other tetrahedra (eg, mica minerals); in tektosilicates or framework silicates, all 4 oxygen atoms of each tetrahedron are shared (eg, quartz).
Author ANN P. SABINA
Links to Other Sites
Dig into this extensive online resource about minerals and the mining industry. Features the latest news and information about Canadian and international mining companies, mineral commodities, mining properties, and much more. Check the "Dictionary" link at the bottom of the page.
Mineral Deposits of Canada
An overview of the economic and geological contexts of Canada's major mineral deposit types. Scroll down the page for various tables and geological maps of Canada. From Natural Resources Canada.
Back issues of “Canadian Rockhound,” a free online magazine about the world of rocks, minerals, fossils, gemstones and Canada's geology. From Library and Archives Canada.
Life of a Rock Star
This site tells the story of an extraordinary group of scientists who tramped, paddled and rolled across Canada in the nineteenth century to study the geology of Canada's varied terrain.
Cape Breton Miners' Museum
Dig into the history of Cape Breton coal mining at the Miners' Museum website. Features an extensive glossary, great photographs, and notes about the geological development of Cape Breton's coal field. The acclaimed "Men of the Deeps" choir performs at the museum during the summer season.
Alberta Geological Survey
The website for the Alberta Geological Survey offers an extensive collection of maps, reports, newsletters, and other publications about the geology of this prairie province.
A History of Mining and Mineral Exploration in Canada
Click on the cover image to view an online copy of a comprehensive report that traces the emergence of Canada's mineral industry. From Natural Resources Canada.
The Beautiful Minerals Poster Series
A great site for photographs of Canadian mineral samples and online illustrated articles from the magazine "Elements." Every issue explores a theme of broad and current interest in the mineral sciences. From the Mineralogical Association of Canada.
Exploration Criteria For Coloured Gemstone Deposits in the Yukon
This jewel of an article traces the history of gemstones from the ground to the jewellery store showcase. Learn about rubies, sapphires, emeralds and other popular coloured gemstones. Great illustrations are sprinkled throughout. From the Yukon Geological Survey. A very large PDF file.
Strathcona Provincial Park
This nicely illustrated website traces the dynamic geological history of British Columbia’s first provincial park. Learn about rocks in the park, fossils, plate tectonics, volcanoes, glaciers, and more. From the BC Geological Survey.
Prospectors and Developers Association of Canada
The website for the Prospectors and Developers Association of Canada, a national association representing the interests of the mineral exploration and development industry. Check out the "Mining Matters" section for learning activities about mining and minerals.
Glossary: Rock'n Metal
A bilingual glossary of terms related to mining and metalurgy. From the website for the Virtual Museum of Canada.
Glossary: Uranium Mining
Uranium Miner's Glossary of uranium mining and general mining terms.
A glossary of terms related to the mining industry. From the website for The Northern Miner.
The website for PotashCorp, the world’s largest fertilizer company by capacity, producing the three primary crop nutrients – potash (K), phosphate (P) and nitrogen (N). As the world’s leading potash producer, this company is responsible for about 20 percent of global capacity.