The Aggregates & Recycling Information Network

Glossary: G

  • Gabbro

    Coarse-grained, plutonic rock, consisting essentially of calcic plagioclase and pyroxene, sometimes with olivine.

  • Gabion

    A wire cage containing rock which can be used to give protection against erosion or to counteract slope instability.

  • Galvanometer

    An instrument designed to detect and indicate the magnitude of small currents.

  • Gangue

    The material of no apparent value associated with minerals in lodes or veins.

  • Gap-graded Aggregate

    A material in which particular size fractions are absent.

  • Gape

    The distance across the crusher feed opening between the fixed and moving members.

  • Garnet

    Usually red gemstone, metamorphic mineral.

  • Gas Welding

    Any metal welding process in which a combination of gases are used to obtain a hot flame; the most commonly used process employs the oxy-acetylene combination.

  • Gate Valve

    A stop valve which closes a pipe to the flow of fluid by means of a plate which moves in a plane at right-angles to the direction of flow. When closed, the plate seals the pipe and, when open, the full bore of the pipe is available for flow and resistance to flow is less than with other types of valve.

  • GDO

    abbr. General Development Order

    The Town and Country Planning Development Order 1988.

  • Gear Pump

    A small pump consisting of a casing enclosing a driven gear wheel in mesh with a second gear wheel, the fluid being carried from the suction to the delivery side of the pump in the spaces between the teeth.

  • Gearing

    The relationship between the amounts invested in a business by its owners as equity and by others as debt.

  • Geophone

    An instrument used for detecting the passage of sound waves through the strata.

  • Geophysical Prospecting

    The making and interpretation of certain physical measurements to obtain information on the subsurface geological structures.

  • Geophysics

    The study of the Earth’s physical characteristics by the use of instruments to determine physical properties such as relative density, electrical conductivity, magnetic susceptibility, seismic wave propagation etc.

  • Geotechnical Appraisal

    An exercise conducted on a tip or excavation to determine whether movement or collapse would present a significant hazard. If so, the tip is notifiable and a geotechnical assessment is required.

  • Geotechnical Assessment

    A detailed study by a geotechnical specialist of the design and construction of a tip or excavation to determine the probability of failure.

  • Geotextile

    A synthetic fabric used as a filter in groundwork.

  • GGBS

    abbr. ground granulated blast-furnace slag.

  • Giga-

    A prefix indicating multiplication by one thousand million.

    abbr. G

  • Glacial

    Formed by ice action.

  • Glacial Drift

    Material transported and deposited by glaciers.

  • Glauconite

    Hydrous silicate of iron and potassium with magnesium and aluminium, occurring in many sandstones, giving them a green colour.

  • Glory Hole

    An open-pit method of excavation in which underground drives are put in below the area to be excavated and raises are then driven into the excavation site; the raises are used as passes for the broken ore or rock which is drawn off and transported as required.

  • Gneiss

    A metamorphic rock with constituents similar to that of granite but having a foliated or banded structure.

  • Grab Sample

    A random sample taken from a stockpile or consignment when there is insufficient time or labour to take a representative sample. Taken by an experienced sampler, it can be used to obtain a good estimate of the quality of the material.

  • Gradient

    The rise or fall per unit horizontal length of a road, railway etc. Gradient may be expressed as a ratio or as a percentage.

  • Grading
    1. The percentage by weight of different sizes present in an aggregate, established by sieve analysis and expressed on a grading curve.
    2. Shaping the ground surface, usually by means of a grader or bulldozer.
  • Grading Curve

    A graphical representation of the proportions of different particle sizes in a material. There are many ways of recording the results of a sieving test, the most common being that of plotting the cumulative percentages of material passing through (or retained on) the sieves against apertures size. Particle size is usually plotted on a horizontal logarithmic scale and percentages on a vertical arithmetic scale.

  • Grain
    1. Degree of fineness or coarseness of texture.
    2. Quarrying term, cleavage.
    3. Direction along which igneous rocks can be split.
  • Granodiorite

    Igneous rock of medium grain size; contains abundant quartz and plagioclase over orthoclase; also dark coloured minerals (eg hornblende, biotite); an igneous rock with mineralogy intermediate between granite and diorite.

  • Granulator

    A jaw crusher with a high width/gape ratio, normally used for the reduction of oversize in gravel deposits at low capacity.

  • Granulite

    Metamorphic rock of even-sized granular minerals.

  • Graticule

    The set of cross-hairs fitted into the diaphragm of a surveying instrument telescope.

    Also: reticule 

  • Gravel Pump

    A centrifugal pump with renewable impellers and linings for raising gravel and other abrasive materials. Many pumps of this type are rubber-lined.

  • Gravimeter

    An instrument used in gravity surveying to measure changes in the value of gravity over an area.

  • Gravity

    The force which attracts matter towards the centre of the Earth. The acceleration due to gravity is 9.81m/s/s at sea level.

  • Gravity Concentration

    Processes for sorting granular material by forces which depend on differences in the densities, shapes and sizes of the particles.

  • Gravity Surveying

    A method of geophysical prospecting using a sensitive instrument known as a gravimeter to measure small variations in the Earth’s gravitational field caused by density differences in the underlying rocks.

  • Greensand
    1. Sand or sandstone coloured with glauconite.
    2. Lower and upper subdivision of Cretaceous rocks often containing glauconite.


  • Greenstone

    General term for basic and intermediate igneous rocks in which metamorphism has produced abundant chlorite and epidote.

  • Greywacke

    A dark-coloured, poorly graded, argillaceous sandstone.

  • Grid
    1. A fixed heavy-duty screen. Also: grizzly
    2. A rectangular layout of straight lines used in locating points on a plan.
  • Grit
    1. Term which, when applied to describe dispersions of small solid particles in air or other gas, refers to those particles which are larger than 76µm.
    2. Small hard fragments of mineral aggregate for application to a road surface.
  • Gritstone

    Sandstone with angular, usually coarse grains.

  • Gritter
    1. A machine or attachment to a lorry for applying chippings or small aggregate in a uniform layer to the surface of a road, as a surface dressing.
    2. A machine for distributing small chippings, sand or salt over a road surface to counteract slipperiness caused by frost, snow etc.
  • Gritting

    The operation of spreading grit or similar material on a road surface to reduce the possibility of skidding.

  • Ground Water

    Water which has penetrated from the surface and filled the pores and fissures of the strata up to the water table.

  • Grout

    Fluid or semi-fluid cement slurry for pouring into masonry joints, injection into the ground and filling the space surrounding foundation bolts.

  • Grout Box

    The wood or metal box in a concrete foundation, with a metal plate at its lower end through which the foundation bolt passes.

  • Grouted Macadam

    A form of road construction made of coarse aggregate into which a bituminous binder or a mortar of Portland cement and sand is poured after spreading the aggregate.

  • Grouting
    1. The pouring of grout into masonry joints and the space surrounding foundation bolts, also its injection into fissured ground.
    2. Introduction of a liquid binder into the interstices of a material.
  • Guard

    A fence or other device fitted to the moving parts of machinery to prevent injury to operators.

  • Gunpowder

    A low explosive composed of sodium or potassium nitrate, charcoal and sulphur.

    Also: black powder

  • Gypsum

    Hydrated calcium sulphate, CaSO4.2H2O, associated with other evaporite minerals in extensive beds. Used in the manufacture of plaster-board, Portland cement, fertilizer etc.