WHAT ARE MINERALS?
The rocks which form the Earth, the Moon and the planets are made up of minerals.
Minerals are chemical elements or compounds which occur naturally within the crust of the
Earth. They are the discrete crystalline particles of which nearly all rocks are made.
Minerals are solid substances made up of atoms with an orderly and regular arrangement,
which is the basis of their crystalline state. Because of their orderly atomic arrangement
it is also possible to express the composition of a mineral as a chemical formula.
Minerals are inorganic substances (not derived from living
things) composed of elements such as silica, oxygen, aluminium, iron, etc. Fossil fuels
such as coal, oil and natural gas are organic (formed from once-living matter) and hence
are not minerals in the strict sense.
Minerals provide the elements essential to life, the metals of industry
and the materials for building (Tables 2-7). The calcium and phosphorus in bones and the
iron in blood are made available to the body through plants which extract these elements
from minerals in the soil.
Mineralogists (geologists who study minerals) have identified
nearly 3000 minerals. About 100 of these are regarded as common minerals and less than 20
can be found everywhere.
Nearly all rocks are composed of minerals (some contain glass or organic
matter) but it is rare to find good mineral specimens. These tend to occur in gaps,
cavities and fractures within the rocks where the crystals have been unobstructed (have
much free space) during their growth. Rocks can be formed from a combination of several
different minerals or a single mineral can make up the bulk of a rock, for example,
limestone or marble is mainly composed of the mineral calcite (CaCO3).
Many minerals are found as beautiful crystals. Crystals are
formed when minerals are free to grow without constraint. Crystal faces reflect the
regular atomic arrangement of the mineral. The incredibly regular arrangement of crystals
has been recognised for about 200 years but the internal structure of minerals has only
been determined this century by the use of X-rays. The regularity of crystals is due to
the angle between the same two faces of all crystals of the same mineral species being
constant, even though the faces may look variable in size and shape. This crystal
structure determines the physical properties of minerals. Crystals are symmetrical and can
be grouped according to their symmetry into seven crystal systems. The study of crystals
and crystal systems is called crystallography.
Minerals vary in colour and in the way they look and feel. Some minerals
are hard and sparkle and shine like glass. Others are slippery and soft or hard and
scratchy. The way minerals look depends on their interaction with light, and these optical
properties can be used to classify and identify minerals. These include properties
such as transparency, reflection and refraction, lustre, colour, streak (colour of the
powdered mineral) and fluorescence.
Minerals can be classified according to their hardness as
described by Moh's Hardness Scale (Table 1). In 1812, F. Mohs arranged ten minerals in
order of hardness so that each mineral can be scratched by the one following it on the
scale. Thus talc is the softest and diamond is the hardest.
Table 1. Moh's Scale of Hardness
||Objects of Similar Hardness
||Plaster of Paris
Minerals also occur as aggregates of crystals that
rarely show perfect crystal shapes. The form of the aggregate can be useful for
identification, i.e. whether they are fibrous, dendritic, lamellar or foliated, etc.
The density or specific gravity of a mineral depends on several
factors including the kind of atoms in the structure and how closely they are packed. For
example, the minerals tridymite and quartz are both silica (SiO2) but quartz, the closely packed form, has a specific gravity of 2.65 at room
temperature whereas tridymite, with a more open structure, has a specific gravity of 2.26
at room temperature.
Other properties that mineralogists use when identifying and classifying
minerals are related to how they break i.e. cleavage (breaks along a planar surface
related to the structure and parallel to a possible crystal face) and fracture
(broken surface is irregular), magnetic, electrical and radioactive properties.
The composition of a mineral can be expressed as a chemical formula
which is a simple way of expressing mineral chemistry. The mineral chemistry can be used
to further classify minerals. Silicate minerals (combinations of silicon and oxygen
with other elements) are the most abundant rock-forming minerals. Silicate minerals that
commonly occur in the rocks of Fiji include feldspar, mica, olivine, pyroxene and
amphibole. Quartz is simply a combination of oxygen and silicon, without other elements.
TYPES OF MINERALS
There are two types of minerals: metals and non-metals, and they have
different properties as outlined below.
Strong, can support heavy loads without breaking.
Conduct heat and electricity.
Opaque - do not allow light to pass through.
Malleable - can be bent without breaking.
Ductile - can be stretched into wire.
Weak, shatter when hit with a hard object.
Most do not conduct heat and electricity.
Can be transparent, translucent or opaque.
ORIGIN OF MINERALS AND ROCKS
Most minerals crystallise from some sort of solution. Some of the ways
minerals can form are from :
(i) cooling of magma (complex solutions of molten rock materials within
the earth) or lava (complex solutions of molten rock material that reach the Earth's
(ii) cooling of subsurface solutions involving hot water or hot gases,
including steam, as in many mineral veins and metallic ore deposits;
(iii) hot vapours condensing to form minerals, such as sublimates of
sulphur near volcanic vents;
(iv) chemical reactions with previous minerals, such as the hydrothermal
alteration of feldspar to mica, or the oxidation of iron-bearing minerals in the zone of
chemical weathering at the earth's surface;
(v) replacement or substitution of an earlier-formed mineral;
(vi) recrystallisation of earlier-formed minerals to form new compounds
under changed temperature and pressure conditions; or
(vii) evaporation of water solutions.
Many minerals are useful to us. A useful mineral from which a valuable
element can be extracted is called an ore mineral. Ore is a rock that has enough
concentration of one or more such minerals to make it profitable to mine it. Mineral ores
are the source of all the metals and many other substances that we use every day (Table
5). To obtain these Earth resources we have to take them out of the Earth by mining and
then change them into different substances. Ore also contains economically useless gangue
minerals which have to be removed before the ore minerals can be concentrated.
USES OF MINERALS
Minerals have always been used by humans in almost every facet of daily
living. Primitive peoples who used rocks to form weapons and other useful tools in the
Stone Age. Then, as people discovered the methods of isolating metals from their mineral
ores, "technology" and "civilisation" advanced successively through
the Copper, Bronze, Iron, Steel and Atomic Ages. At each step, minerals assumed
progressively greater importance.
The tables below (Tables 2-7) represent some of the common minerals and
their many uses in our everyday lives.
Table 2. Uses of Some Common Metallic Minerals
||METALLIC MINERAL ORES
||Beverage and food cans, furniture, buildings, electrical
appliances, air conditioners, ships, motor vehicles, aircraft and other transport
equipment, cooking utensils, aluminium foil, high voltage power transmission lines (with
||Plating household appliances, motor cars, to harden and
strengthen steels and cast iron, stainless steel for automotive, construction and chemical
||Native Copper Chalcopyrite Chalcocite
|All electrical appliances, telephone cables, radios, TV
sets, motor vehicle electrical systems, motors for all purposes, ornamental items made of
brass and bronze, plumbing pipes and tanks, roofing.
||Currency, jewellery, dentistry, electronic and space
|Hematite Magnetite Limonite
|Household appliances, motor vehicles, buildings, bridges,
office equipment, beverage and food cans and other containers, tools, farm and factory
machinery, transport equipment, building materials.
|Storage batteries, petrol additives, buildings, bridges,
office equipment, beverage and food cans and other containers, tools, farm and factory
machinery, transport equipment, building materials.
|Stainless steel, motor vehicles plating, aircraft,
transport equipment, household appliances, electrical machinery, ships, coinage, numerous
alloys particularly where corrosion resistance and hardeners are important requirements.
||Native Silver Argentite
|Photographic film and developing paper, silverware,
jewellery, industrial refrigerators, coinage, batteries, electronic solder in aircraft.
||Tin plate, solder, pewterware, in bronze, in electrical
equipment, in pigments for pints and plastics and in dry-cell batteries.
|Ti metal for engines, Ti pigment for paints, paper,
plastics, welding electrodes.
||Pitchblende or Uraninite,
|Power generation, production of radioisotopes for research,
industry, agriculture and medicine.
|Galvanised roofs, fences, car bodies, zinc die castings for
carburettors, motor vehicle grills, household appliances, door handles, zinc oxides for
tyres and paints, rolled zinc
Table 3. Uses of Some Non-Metallic
||Fireproof fabrics, paper, brake linings
||Oil-well drilling muds, glass, paint
||Flux, glass, detergents, chemicals
||Bricks, tiles, pottery, fillers for paint, rubber and
||Drills, abrasives, gems
||Flux for glass manufacture, porcelain, enamel, tile glazes,
||Abrasives, gems, watches, jewels
||Pencils, batteries, foundry facings, crucibles, lubricants
||Wallboard, plaster, soil improvement, retarder in portland
||Food, Chlorine for water treatment, sodium hydroxide for
||Cements, rubber, foundries, refractory brick
||Electronics, radio tubes, electrical insulation, cement,
||Broadcast frequency control, silica glass
||Fertiliser, sulphuric acid, paper making, bleaches
||Toiletries, ceramics, paint, paper
||Sound insulation in plaster and loose fill, plastics
Table 4. Minerals Used in a School Room
||Made of wood covered with paint containing abrasive
minerals such as ground pumice. Duster made of synthetic fibre.
||Made from clays, shale, limestone, bauxite, hematite,
||Dried and moulded paste of calcium carbonate and gypsum
||Frames of steel painted or galvanised with zinc
||Made from silica sand, limestone, borate salts, soda ash
and feldspar minerals
||Filled or coated with industrial minerals like kaolin,
calcium carbonate and talc
||Graphite and clays in pencils. Ballpoint pens use brass,
tungsten and plastic. Ink uses calcium carbonate and fillers.
||Wallboard of gypsum joined by cement with gypsum, mica,
clays and calcium carbonate
||Saws and planes made from steel are used to cut wood. Wood
is sanded with sand paper embedded with emery, corundum and garnet powders
Table 5. Minerals Used in a Bathroom
||PVC and plastics from petrochemicals and components of
||Sterilants and bleaches made with chlorine and halite.
Scouring and cleaning liquids and soap made from soda ash, borax, limestone, halite,
sulphur, clays, diatomite, pumice and petrochemicals
||Talc in powder, magnesium carbonate and silica help flow
and fragrance. Lipsticks use talc and calcium carbonate
||Marble and granite or ceramic
|Hand basin and bath
||Porcelain made using silica, limestone, borate salts, soda
ash and titanium minerals
||Clays used as thickeners
||Brass, steel or aluminium with plastic components. Chrome
uses chromium, cadmium, sulphur
||Ceramics are made from kaolin, silica, feldspar, talc.
Manganese, cobalt, antimony and iron oxides give colour. Putty uses limestone and gypsum
||Pulp is processed with sulphur, soda ash, limestone, clay,
talc and titanium minerals
||Calcium carbonate, zeolites, sodium carbonate and clays.
Gels use silica.
Table 6. Minerals used in Sporting
||Frame, wheels and gearing are of steel, aluminium, chromium
and titanium minerals. The plastic seat and helmet are from petrochemicals. The tyres made
using sulphur and petrochemicals
||Iron, chromium, nickel, petrochemicals, aluminium. Pads and
helmet use copper, zinc, petrochemicals and iron.
||Plastics, dyes, synthetic fibres and printing ink for the
tough fabric come from petrochemicals. Petrochemicals and sulphur used in the rubber
||Made with zinc compounds and titanium oxides
||Lenses of glass or plastics from petrochemicals. Frames of
chromium, brass and gold
||The plastics, nylon and synthetic fibres from
petrochemicals, while the metal parts are aluminium, steel or brass.
Table 7. Minerals Used in Furniture,
Fittings and other Equipment
||Made of aluminium, chromium, cobalt, tantalum, and
||Wool is cleaned with clays, soda ash, zeolite or
petrochemicals. Synthetic fibres and dyes come from petrochemicals
||Frame made of steel painted or galvanised with zinc.
Coverings of vinyl and synthetic fibres derived from petrochemicals
|Computers and electronics
||More than 33 minerals and elements ranging from aluminium
to zirconium. The silicon chip is made from silica or quartz
||Made of natural or synthetic fibres. Tracks are of
aluminium or steel.
||Made from steel or brass (alloy of copper and zinc)
|Door stopper and other rubber items
||Made from petrochemicals, sulphur, limestone and clays
||Sulphur; colours from mineral mixtures like iron filings
and charcoal (gold sparks), strontium and sodium (orange), barium (green), strontium
(red), copper (blue), sodium (yellow), and others. Fine aluminium powder is used for a
||Concrete uses lightweight aggregate such as perlite,
vermiculite, zeolite or expanded shales. Floors covered with ceramic, marble or granite
|Light bulbs, fluorescent tubes
||Made from glass. Metal fittings of steel, copper and lead.
Elements of tungsten and rare earth metals.
||Made of steel, copper and brass, with plastic components
||Made from petrochemicals, and also contain clays, limestone
||Contain minerals like kaolin, iodine, and many others
|Metallic window frames
||Made of steel and aluminium
||A telephone handset uses 42 different minerals!
||Most are made from petrochemicals, but contain minerals
such as calcium carbonate (from limestone), clays, hematite, talc, mica, petrochemicals,
and colouring pigments from titanium minerals
||Steel or aluminium frame covered with plastic sheeting from
||Sheeting made by floating glass on molten tin.
NECESSITY OF MINERALS
Today, mineral resources play a role second in importance only to that
of agriculture, and there are thousands of uses for the various materials of the Earth.
There isn't much that one can think of that doesn't come from some sort of mining process
and it can honestly be said that:
"If it's not grown, it's
Virtually no aspect of our lifestyle could be sustained without
minerals. Minerals are used in every facet of our daily living from food production and
processing, building, providing shelter/housing to transport, communications, medicine and
EXPLORATION AND MINING
Exploration is the search for mineral deposits containing sufficient ore
to be economically mined. Geologists use all available geological and geophysical tools to
assist exploration. Ore minerals are extracted from the Earth's surface and from
underground by mining. The ore is then milled, (crushed), processed and refined to produce
the metal or non-metallic product.
FIJI'S MINERAL WEALTH
Fiji's mineral wealth includes gold which is mined at Vatukoula and
provides the fourth largest source of foreign exchange. There are plans to open gold mines
at Mt Kasi in south-west Vanua Levu and at Tuvatu near Nadi. Advanced exploration is also
currently underway at Namosi for copper-gold, at Wainivesi for marble and in other parts
of Fiji for gold. In addition, there is quarrying of rock and sand for road metal,
concrete aggregate and landfill and of coral sand for cement manufacture. Clay is used by
many villagers to make pottery.
SUGGESTIONS FOR FURTHER READING
Allison, I. S. & Palmer, D. F. 1980. Geology, the science of a
changing Earth. VII Edition. McGraw-Hill Inc.
Cox, K. G., Price, N. B. & Harte, B. 1974. An Introduction to the
Practical Study of Crystals, Minerals and Rocks. Rev. 1st ed., John Wiley & Sons
Inc., New York.
Hamilton, W. R., Woolley, A. R. & Bishop, A. C. 1984. The Hamlyn
Guide to Minerals, Rocks and Fossils. The Hamlyn Publishing Group Ltd, London.
Lye, K. 1979. Minerals and Rocks, (Kingfisher Guides), Ward Lock
|MRD Information Notes 8
Director : A. Rahiman
|Devika P. Reddy