O — Dictionary of Quarrying Terms

OBM: abbr. ordnance bench mark.

OCCS: abbr. opencast coal site

OD: abbr. ordnance datum.

OES: abbr.occupationa exposure standard. The concentration of airborne substance at which level it is not likely to be injurious to health.

0S: abbr. Ordnance Survey.

0SS: abbr. open-side setting. see ‘setting’. It regulates the size of the largest particle released from a crusher.

offset: A horizontal distance measured at right-angles to a survey line to locate a point adjacent to it.

ohm: The resistance between two points of a conductor when a constant difference of potential of one volt, applied between these two points, produces in this conductor a current of one ampere. Symbol: Ω

ohmmeter: An instrument used to measure the resistance between two points in a circuit or of a single component when the part to be measured has been isolated from the supply.

olivine: Magnesium iron silicate, (MgFe)2Si0₄, occurring in basic igneous rocks, eg olivine-basalts; typically dark olive-green to brown in colour.

oolites: A group of sedimentary rocks consisting of oolitic limestones, clays, shales and sandstones made chiefly of ooliths cemented together. Uses include building stone, iron ore, brickmaking clays and fuller’s earth.

ooliths: Ellipsoidal or spherical accretionary bodies, usually less than 1mm in diameter, composed of concentric layers of calcite, aragonite or iron carbonate.

open circuit: 1 A flow line in which the solid particles pass from one appliance to the next with no fraction being returned for retreatment. 2 The state of an electrical circuit when there is a break in continuity.

operator: the person (or company) in overall control of the working of a quarry.

ordinary lay: A term applied to a steel-wire rope in which the wires forming each strand twist in the opposite direction to that of the strands, making it unlikely that it will untwist.

ordinary prescribed mixes: Concrete mixes for which the proportions of aggregate, cement and water have to be in accordance with the quantities specified in BS 5328:1981.

ordinary shareholders: The owners of the business. These shareholders participate in the distribution of the profit remaining after payment of the preferential shareholders. This dividend is declared as a percentage of the par, or nominal value of the shares.

ordnance datum: The land-levelling datum, being the mean sea level determined at Newlyn, Cornwall, the use of which makes comparison of the heights of installations throughout the UK possible.

Ordovician: A period of the Palaeozoic era, ranging from 505 to 435 million years ago.

ore: Solid mineral of actual or potential economic interest.

orthoclase: Potassium aluminium silicate (KAlSi₃O₅) a member of the feldspar family. Important as a constituent of acid igneous rocks. Used in the manufacture of glass, pottery etc.

outcrop: The area where part of a rock stratum, or any other deposit, appears at the surface, any cover of soil being ignored.

overbreak: Excessive breakage of rock beyond the desired excavation limit.

overburden: Material, whether consolidated or not, which has to be removed before a mineral can be worked.

overburden ratio: The ratio of the vertical thickness of the overburden to the thickness of the mineral to be mined in a stratified deposit.

overcurrent protection: Protection of a system against excessive electrical currents.

overhead: The costs not directly associated with a unit of production which are apportioned over a range of operations or products; the indirect costs.

overflow: That proportion of the feed discharged from the screen without having passed through the apertures.

overload: In electrical or mechanical engineering, a load greater than that for which the plant is designed.

oversize: Material in a product of a size greater than the upper nominal size; may be expressed as a percentage of the product.

owner: The owner of a quarry within the meaning of section 181 of the Mines and Quarries Act 1954.

oxidizer: An ingredient in an explosive or blasting agent which supplies oxygen to combine with fuel to form gaseous or solid products of detonation. Ammonium nitrate is the most common oxidizer used in commercial explosives.