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Ministry of Energy Mines and Responsible for Core Review
Glossary
Bed
a layer of rock, usually sedimentary or volcanic.
Bedrock
a term used to describe the solid rock that underlies soil or other unconsolidated material.
Cement
mineral matter deposited between rock-particles so that they stick together as a solid mass. The commonest cements in sedimentary rocks are silica (quartz) and calcite.
Crystal
a homogeneous solid with a definite chemical composition and ordered atomic structure, bounded by naturally-formed plane faces. One of several forms a mineral can take.
Dyke (or dike)
a sheet-like igneous intrusion normally intruded in a more or less vertical position and so crosscutting layering in host rocks. Similar intrusions that parallel layering are called sills. Rocks forming dykes are usually fine to medium-grained or porphyritic.
Earthquake
a naturally occurring shaking motion of the Earth's surface. Earthquakes are caused when stress, building up within rocks of the Earth's crust, is released in a sudden jolt.
Erosion
the general term for the wearing away of rocks including loosening, breaking up, physical and chemical disintegration, and solution of the rock. Also includes the transport of the fragments.
Extrusive rocks
the products of igneous activity at the Earth's surface. Includes both lavas which are outpourings of molten rock on the surface, and fragmental rocks (pyroclastics) made up of solid, broken fragments ejected from the volcano.
Foliation
a layered arrangement of minerals in a rock, usually metamorphic.
Fossil
the remains, impression or trace of parts of an animal or plant in a rock.
Geology
the science of the Earth, its composition, structure, processes and history.
Glacial sediments
sediments which form as a result of the actions of ice or glaciers.
Hypabyssal rocks
intrusive igneous rocks formed at shallow depths within the crust. They are usually fine to medium-grained or porphyrytic.
Igneous
rocks formed by the crystallization of minerals from molten material or magma as it cools
Intrusive rocks
an igneous rock formed by the forceful movement and cooling of magma into a body of rock below the Earth's surface. Includes both hypabyssal and plutonic rocks.
Metamorphic rocks
rocks which have formed from pre-existing rocks due to changes in temperature, pressure, stress or chemistry.
Mineral
minerals are naturally occuring inorganic substances with a definite and predictable chemical composition and physical properties. More than two thousand three hundred different types of minerals have been identified. Luckily many are rare and the common rocks are made up of a relatively small number of minerals.
Petrology
the study of rocks, their properties and origins.
Physical Properties of minerals
the physical properties of a mineral reflect in a close way the crystal structure and chemical compositon of the mineral. However, they are often easier to determine. They are of great practical significance not only to aid in the identification of the mineral, but also in determing the possible industrial uses of the mineral. The commonest physical properties include:
form - the external appearance of a mineral or aggregates of the mineral, e.g., crystalline, fibrous, stalactitic, dendritic (plant-like), etc.
colour - colour observed in a mineral sample in white light. With experience, colour can be one of the most valuable of diagnostic properties.
streak - the colour of the powdered mineral, which may differ from the body colour of the unpowdered mineral. Usually determined by drawing the mineral across a piece of unglazed, white porcelain known as a streak plate.
transparency - whether the mineral allows light to pass through it. Minerals can be transparent, translucent or opaque.
hardness - the ability of a mineral to resist abrasion or scratching. Measured on a relative scale from 1 - 10 known as Mohs' Scale in which minerals of higher number scratch those of lower numbers. For simple field determinations, a fingernail has an hardness of about 2.5 and the blade of a penknife about 5 - 5.5.
lustre - The characteristic appearance of a mineral in reflected light, e.g., metallic, pearly, earthy, greasy, etc.
cleavage and fracture - the way that the mineral breaks; if it breaks along planar surfaces related to the crystal structure it is said to show cleavage, but if it breaks irregularly is said to show fracture.
density - the measure of the mass per unit volume of a mineral. In simplest terms, some minerals will be heavier than others for similar sized samples, e.g. gold is denser than quartz.
Plutonic rocks
intrusive igneous rocks that form at some depth. They are usually medium to coarse-grained and include rocks such as granite and gabbro.
Porphyry
an igneous rock in which comparatively large crystals, phenocysts, occur within a distinctly finer-grained ground mass.
Rock
a consolidated collection or aggregate of mineral material .
Rockhound
an amateur rock and mineral collector.
Sedimentary rocks
rocks formed by the accumulation of fragments, or the precipitation of dissolved material, that result from the weathering of pre-existing rocks.
Unconsolidated
loose sediment that has not been cemented or otherwise converted to solid rock.
Vein
a crack or fissure in a rock that is infilled with mineral matter. Veins can vary in thickness from less than a millimetre to several tens of metres. Similarly, thay can vary in length up to several hundreds of metres.
Vesicular
decribes a volcanic rock that has holes, vesicles, that were once gas bubbles in the molten lava. The holes are often later infilled with minerals, such as calcite or quartz, and are then referred to as amygdales.
Volcanic rocks
rocks which result from volcanic action at, or near, the surface of the Earth such as lava flows or ash deposits.
Volcano
a hill resulting from extrusive igneous activity. Volcanoes are described as active (presently or recently in action), dormant (inactive for some time, but liable to erupt again) or extinct (no longer active and unlikely to erupt again).
Weathering
the disintegration of rocks on the Earth's surface by the action of rain, frost, heat, wind, etc.