M — Dictionary of Quarrying Terms

MEL: abbr. maximum exposure limit. The maximum concentration of airborne substance to which employees may be exposed under any circumstances. See also ‘OES’

MHO: Manual handling operation

MPA: abbr. mineral planning authority

macadam: Uniformly graded stone compacted to form a road named after 19th century engineer John MacAdam.

machine-hour: The running of a machine or plant for one hour.

machine tools: Metal-cutting machines such as lathes, drills, grinders, planers etc.

magazine: see ‘explosives store’.

magma: Naturally occurring deep molten rock material from which igneous rocks are formed on cooling.

Magna Primer: The trade name for a primer cartridge which incorporates, in addition to the primer charge, two Magnadet delay detonators and is designed for use in quarry blastholes. It is connected to the special exploder by passing the primary coupling wire through a hole in its centre.

Magnadet: Trade name for a system of initiation of quarry blasts in which the detonator is electrically isolated from outside influences by coupling it, through its own transformer, to a special exploder which provides a high-frequency supply of approximately 15,000Hz. The system offers protection against: dc power sources, normal ac power sources, static electricity hazards, electromagnetic radiation and current leakage.

magnetic field: The space surrounding a permanent magnet or a conductor carrying an electric current throughout which the forces produced by the magnet or current can be detected.

magnetic flux: The lines of magnetic force which, in theory, make up a magnetic field.

magnetic separator: A device for separating, by means of an electromagnet, magnetic particles in a slurry from the remainder of the particles in the mixture. Used in the recovery of medium in heavy-media separation.

magnetic surveying: A method of geophysical prospecting using a magnetometer to measure variations in the Earth’s magnetic field over the area under investigation. Magnetic anomalies plotted on a map are used to indicate the probable position of rocks containing magnetic minerals in the sub-surface structure.

magnetite: An iron ore mineral, Fe₃0₄ which occurs as a primary constituent of most igneous rocks.

magnetometer: An instrument for measuring the intensity of the Earth’s magnetic field. It is used in geophysical prospecting when it may be carried in a low-flying aeroplane where large areas are being investigated.

malleability: The property of a metal which may be bent or hammered without breaking.

man-hour: The labour of one man for one hour.

manager: A person appointed by the owner as manager of a quarry or part of a quarry under either section 98,102 or 103 of the Mines and Quarries Act 1954.

manager’s rules: Rules made by the manager which lay down procedures which will ensure that operations at the quarry can proceed without endangering the workforce or the public.

manganese steels: Steels which contain more manganese than is usually present in plain carbon steel. The steel containing 11% to 14% Mn is called austenitic manganese steel or Hadfield’s manganese steel. This steel possesses high strength and resistance to wear after work-hardening. Used for crusher jaws, gyratory crusher concaves and mantles, bucket teeth etc.

mantle: 1 The cast steel liner, usually of manganese steel, which sits on the head of a gyratory crusher. 2 The rock layer between the Earth’s crust and the core.

marble: Metamorphic rock produced from limestone by recrystallization caused by heat and pressure.

marginal costing: An accounting technique whereby the effect on costs of a small increment or decrease in output may be estimated. Assuming that the change in output does not affect the elements comprising fixed costs, the marginal cost will be the variable cost per unit of output.

marine band: A bed which contains marine fossils.

marine-dredged aggregates: Sand and gravel obtained by dredging marine deposits which have been extensively and satisfactorily used in the manufacture of concrete. The chloride content must be checked frequently to reduce the risk of corrosion of steel reinforcement.

marl: A calcareous clay or mudstone.

Marshall asphalt: A widely used design for asphaltic concrete originally conceived by Bruce Marshall of the Mississippi State Highway Department.

Marshall test: An unconfined compression test on asphalt samples. The point of failure of the compacted mix specimen gives the stability value while the compression at this load gives the flow value.

mass: The quantity of matter in a body. Unit: kilogramme (kg).

massive rock: Rock without stratification, cleavage or schistosity; particularly applied to igneous rock-bodies but can be used to describe sedimentary rocks with thick or obscured bedding.

matrix: The finer-grained material between the larger particles of a rock or the material surrounding a fossil or mineral.

maximum demand: The highest value of the power or apparent power taken within the account period, eg month or year. Maximum demand is recorded by a maximum-demand indicator which shows the new maximum demand if the demand during any half-hour period exceeds the previous maximum.

maximum-demand tariff: A two- or three-part tariff consisting of a maximum-demand charge and a unit (kWh) charge together with, in the case of the three-part tariff, a service (k VA) charge. The service charge is a fixed charge designed to cover the cost of the supply authority’s installation and is based on the required capacity.

mean value: The arithmetic mean of the instantaneous values of a periodic quantity taken over half a cycle.

mechanical advantage: see ‘force ratio’.

mega-: A prefix indicating multiplication by a million. abbr: M.

Megger: Trade name for a range of insulation resistance testers.

member: A part of a structural framework, eg a beam, a tie etc.

mesh: The aperture in a screen surface, or the size of the aperture.

Mesozoic: The era following the Palaeozoic, ranging in time from 230 to 70 million years ago. It comprises the Triassic, Jurassic and Cretaceous systems.

metamorphic rock: Rock which has been altered by the action of heat, pressure or migrating fluids acting separately or together.

method study: The systematic recording and critical examination of existing and proposed ways of doing work, as a means of developing and applying easier and more effective methods and of reducing costs.

metre: The SI unit of length; equal to 39.37in. Symbol: m.

mica: Complex silicates of aluminium and potassium which are constituents of plutonic and volcanic rocks and which are characterized by their perfect basal cleavage. Used in the electrical industry.

micro-: A prefix meaning one millionth. Symbol: µ.

micro-Deval test: The European standard test upon aggregates for resistance to wear. BS EN 1097 Part 1.

micrometer gauge: A U-shaped instrument for accurately measuring small lengths.

micron: A one millionth part of a metre. Symbol: µ.

middlings: An intermediate product, left after the removal of a clean concentrate and rejected tailing, which is usually subjected to further treatment.

mild steel: Hot-rolled steel which, because of its relatively low carbon content (0.15% to 0.29%), cannot be hardened by quenching but is much more ductile than steel with a higher carbon content.

mill: A machine for crushing or grinding, such as a ball mill or a hammer mill.

milli-: A prefix indicating one thousandth of a unit.

millisecond: The unit of measurement of short delay intervals, equal to 1/1000 of a second.

mineral: A naturally occurring inorganic substance having definite physical and chemical properties.

minimum fusing current: The minimum current which will cause the fuse link to operate in a specified time under prescribed conditions.

misfire: A shot or any part of a shot, which fails to explode when an attempt is made to fire it, or where testing before firing reveals broken continuity which cannot be rectified.

mix design: The choice and proportioning of aggregate, cement and water to produce a concrete with the required properties, the essential elements of which are usually durability and strength.

modular screen decks: Screen decks comprised of numerous small panels held in position by quickrelease pegs, making for easier handling, the ability to localize replacement of worn sections and the use of a combination of apertures where required.

Moh’s scale of hardness: An indication of scratch resistance based on the relative hardness of 10 common minerals which, in order of increasing hardness, are: 1 talc, 2 gypsum 3 calcite, 4 fluorite, 5 apatite, 6 orthoclase, 7 quartz, 8 topaz, 9 corundum, 10 diamond.

mole drain: A drain cut by drawing a mole plough (a vertical blade with a horizontal bullet-shaped cutter at its lower end) attached to a tractor, through the soil.

moment of a force: The turning effect of a force. The moment of a force about a point is the product of the force and the perpendicular distance of its line of action from the point. Units: newton-metres (Nm).

momentum: The product of the mass of a body and its velocity. Units: kgm/s.

monitor: A device for directing a jet of water at high pressure to break down a mineral deposit, eg china clay.

moraine: Unsorted, unstratified glacial drift; the material usually forms two lateral moraines parallel to the sides of the glacier. The ridge formed at the end of a glacier when the ice melts is called a terminal moraine.

motor enclosure: Structure containing an electric motor. The numerous types of enclosure include: drip-proof, totally enclosed, flameproof and pipe-ventilated.

motor rating: see ‘rating’.

motorized scrapers: Single- or twin-engined bowl scrapers which are hydraulically operated. They are used on sites where large quantities of material have to be removed quickly and ground conditions are relatively firm.

movement ratio: The ratio of the distance moved by the effort to the distance moved by the load; may also be called velocity ratio.

muckpile: Rock pile of stone fragmented by a blast. See: ‘rock pile’.

mudcap: In secondary blasting, a charge of explosive fired in contact with the surface of a rock, usually covered with a quantity of mud or other similar substance. See: ‘plaster shooting’.

mudstone: A sedimentary rock consisting largely of hardened clay minerals, blackish and without lamination.

multi-deck screen: A screen with two or more superimposed decks mounted rigidly within a common frame.

multigrade oils: Oils which satisfy service requirements at both low and high temperatures so far as viscosity is concerned. They are allocated a compound SAE number, incorporating the viscosity grading at low temperature (first number) and that at high temperature (second number).

multiplying constant: In tacheometer work, the constant by which the staff intercept is multiplied to obtain the distance between the instrument and the staff.

multi-row blasting: A series of blastholes arranged in rows parallel to the free face. More common in surface mining than in rock quarrying.

multi-strand rope: Wire rope consisting of two or more layers of round strands. The alternate layers of strands are laid in opposing directions to counteract torsional stress and produce a rope with nonspinning characteristics.

muscovite: A light-coloured mineral of the mica group, common in igneous and metamorphic rocks and in some sandstones.

mutual inductance: see ‘inductance’.