Geology Topics
- Aa
- A Hawaiian term for lava that has a rough, jagged, spiny, and generally clinkery surface.
- Abbe Refractometer
- An instrument for measuring directly the refractive index of liquids, minerals and gemstones.
- Absolute Age
- The geological age of a fossil, mineral, rock or event, generally given in years.
- Abyssal Plain
- Large area of extremely flat ocean floor lying near a continent and generally over 4000m deep.
- Aclinic Line
- The line through those points on the earth′s surface at which magnetic dip is zero.
- Active Volcano
- A volcano that is erupting.
- Adhesive Tape
- A tape with a sticky substance on one side.
- Andesite
- Volcanic rock characteristically medium dark in colour and containing 54 to 62 percent silica and moderate amounts of iron and magnesium.
- Angle of Repose
- The maximum angle at which loose material will come to rest when added to a pile of similar material.
- Aquifer
- A permeable region of rock or soil through which ground water can move.
- Aquitard
- A material of low permeability that greatly slows the movement of ground water.
- Archaean
- The geological eon covering about 3.9 billion years ago to 2.6 billion years ago.
- Archaeozic
- The geological period from 4.6 billion to 1.0 billion years ago.
- Argentite
- Naturally occuring Silver Sulphide. An important ore of silver.
- Artesian Well
- A well in which the water in the aquifer is under pressure that raises the water above the point that the well first encounters it.
- Ash Flow
- A turbulent mixture of gas and rock fragments, most of which are ash-sized particles, ejected violently from a crater or fissure.
- Asthenosphere
- The shell within the earth, some tens of kilometres below the surface and of undefined thickness.
- Astronomic Theory of Glaciation
- Theory based on the changing position of the Earth in its orbit around the Sun.
- Barite
- Most commonly found mineral of Barium Sulphate.
- Basalt
- Dark colored rocks formed by the rapid cooling and hardening of lava flows.
- Beach
- Temporary accumulations of sediments that collect between low and high tide marks.
- Bedrock
- A general term for solid rock that lies beneath soil, sediments, or other unconsolidated material.
- Bischofite
- Natural occuring mineral of Magnesium Chloride.
- Brass Lump
- The name miner′s would give to a large lump of fools gold.
- Buddling Dish
- A flat pan or vat used in washing ores.
- Caldera
- A large volcanic collapse depression, commonly circular or elliptical when seen from above.
- Cambrian
- The geological period from 570 million to 510 million years ago.
- Carboniferous
- The geological period from 362.5 million to 290 million years ago.
- Cassiterite
- Dark coloured mineral that is an important ore of Tin.
- Cenozoic
- The geological era covering about 65 million years ago to present day.
- Central Volcano
- A volcano constructed by the ejection of debris and lava flows from a central point, forming a more or less symmetrical volcano.
- Cinder Cone
- The simplest type of volcano, built from particles and blobs of congealed lava ejected from a single vent.
- Clay
- Finely suspended earth mineral sometimes found as an impurity in water.
- Composite Volcano
- A steep volcanic cone built by both lava flows and airborne rocks and ash.
- Compund Volcano
- A volcano that consists of a complex of two or more vents.
- Continental Rise
- The portion of the continental margin that lies between the abyssal plain and the continental slope.
- Continental Shelf
- The portion of the continental margin that extends as a gently sloping surface from the shoreline seaward to a marked change in slope at the top of the continental slope.
- Continental Slope
- That part of the continental margin that lies between the continental shelf and the continental rise.
- Cretaceous
- The geological period from 144.2 million to 65 million years ago.
- Dacite
- Volcanic rock that characteristically is light in colour and contains 62% to 69% silica and moderate a mounts of sodium and potassium.
- Devonian
- The geological period from 408 million to 360 million years ago.
- Dip Equator
- Another name for Aclinic Line or Magnetic Equator.
- Dormant Volcano
- The term is used to describe a volcano which is presently inactive but which may erupt again.
- Drainage Basin
- The area of land drained by a river system.
- Earthquake
- The result of a sudden release of energy in the Earth′s crust that creates seismic waves.
- Echo Sounding
- Measurement of the depth of the ocean by directing a sonic or ultrasonic pressure wave vertically downward and determining the time taken before the echo is received.
- Elutriation
- The process of separating the finer particles of an earthy substance from the coarser and heavier by washing with water.
- Eocene
- The geological period covering about 56.5 million years ago to 35.5 million years ago.
- Extinct Volcano
- A volcano that is not presently erupting and is not likely to do so for a very long time in the future.
- Fools Gold
- Name given to Iron II Sulphide due to its colour and texture.
- Foreshore
- Lies between low and high tide marks.
- Galena
- A Lead Sulphide and the most common ore of lead.
- Geochemistry
- The study of materials and chemical reactions in rocks, minerals, magma, seawater, and soil.
- Geothermal Energy
- Energy made by using underground steam; the steam produces electricity.
- Geothermal Gradient
- The rate at which temperature increases with depth below the surface.
- Geyser
- Boiling hot water that is violently ejected from underground when some of the water is converted to steam.
- Gibbsite
- White crystalline mineral consisting of aluminum hydroxide; a constituent of bauxite and a source of alumina.
- Glacier
- A mass of ice, formed by the recrystallization of snow, that flows forward, or has flowed at some time in the past.
- Global Warming
- The prediction that climate will warm as a result of the addition to the atmosphere of humanly produced greenhouse gases.
- Hadean
- The geological eon covering about 4.6 billion years ago to 3.9 billion years ago.
- Haematite
- A common mineral; a form of iron oxide with the formula Fe2O3.
- Hot Spot
- A region of high heat flow.
- Hot-Spot Volcanoes
- Volcanoes related to a persistent heat source in the mantle.
- Hydrosphere
- All the water on the surface of a planet.
- Hydrothermal
- Pertains to hot water or the action of heated water, often considered heated by magma or in association with magma.
- Hydrothermal Alteration
- Alteration of rocks or minerals by the reaction of hot water with pre-existing rocks.
- Ice Age
- Aperiod characterised by a long term reduction in the temperature of the Earth′s climate.
- Igneous Rocks
- Rocks that are formed from melted rock that has cooled and solidified.
- Interglacials
- The warm periods between ice age glaciations.
- Jurassic
- The geological period from 208 million to 146 million years ago.
- Lava
- Hot liquid rock that flows out of a volcanic vent.
- Leaching
- the process by which soluble materials in the soil, such as salts and nutrients, are washed into a lower layer of soil or are dissolved and carried away by water.
- Maar
- A volcanic crater that is produced by an explosion in an area of low relief.
- Magma
- The melted rock produced inside the earth. When a volcano erupts, magma comes to the surface and is called lava.
- Magma Chamber
- An area filled with magma that lies beneath a volcano.
- Magnetic Declination
- The angle between magnetic north and true north at a given point on the Earth′s surface.
- Magnetic Equator
- The line through those points on the earth′s surface at which magnetic dip is zero.
- Mercalli Scale
- A measure of the intensity of an earthquake. This is a subjective value that varies depending on where the earthquake is observed.
- Mesosphere
- A zone in the Earth between 400 and 670 km below the surface separating the upper mantle from the lower mantle.
- Mesozoic
- The geological era covering about 245 million years ago to 65 million years ago.
- Meteor
- A meteoroid that has entered Earth′s atmosphere.
- Meteorite
- The remnants of a meteor after it has actually impacted the Earth.
- Mineral
- A naturally occurring inorganic substance having specified chemical composition and crystalline structure.
- Miocene
- The geological period covering about 23.5 million years ago to 5.2 million years ago.
- Mohs
- A hardness scale developed by F. Mohs in 1812 where the hardness of a material is compared with that of a mineral.
- Monogenetic
- A volcano built by a single eruption.
- Niningerite
- Rare naturally occuring mineral of Magnesium Sulphide.
- Nitromagnesite
- Naturally occuring Magnesium Nitrate.
- Obsidian
- A black or dark-coloured volcanic glass, usually composed of rhyolite.
- Oligocene
- The geological period covering about 35.5 million years ago to 23.5 million years ago.
- Ordovician
- The geological period from 510 million to 439 million years ago.
- Palaeocene
- The geological period covering about 65 million years ago to 56.5 million years ago.
- Paleozoic
- The geological era covering about 570 million years ago to 245 million years ago.
- Permian
- The geological period from 290 million to 245 million years ago.
- Phanerozoic
- The geological eon covering about 570 million years ago to present day.
- Phreatic Eruption
- An explosive volcanic eruption caused when water and heated volcanic rocks interact to produce a violent expulsion of steam and pulverized rocks.
- Phreatomagnetic
- An explosive volcanic eruption that results from the interaction of surface or subsurface water and magma.
- Pillow Lava
- Interconnected, sack-like bodies of lava formed underwater.
- Pitchblende
- The most important Uranium ore.
- Plate Techtonics
- Motion of the plates that make up the surface of the Earth.
- Pleistocene
- The geological epoch covering about 1.64 million years ago to 10000 years ago.
- Plinian Eruption
- An explosive eruption in which a steady, turbulent stream of fragmented magma and magmatic gases is released at a high velocity from a vent.
- Pliocene
- The geological period covering about 5.2 million years ago to 1.64 million years ago.
- Pluton
- Igneous rock bodies that form at great depth.
- Precambrian
- The geological era covering about 4.6 billion years ago to 570 million years ago.
- Proterozic
- The geological period from 1.0 billion to 570 million years ago.
- Proterozoic
- The geological eon covering about 2.6 billion years ago to 570 million years ago.
- Pumice
- A light porous stone of mixed silicates.
- Pyroclastic
- Fragmented rock material formed by a volcanic explosion or ejection from a volcanic vent.
- Pyroclastic Flow
- A hot, dry, fast-moving (10-100m/s) and high-density mixture of ash, pumice, rock fragments, and gas formed during explosive eruptions or from the collapse of a lava dome.
- Pyroclastic Surge
- Turbulent, low-density cloud of hot rock debris and gases that moves over the ground surface at high speed. Lower density than Pyroclastic Flow.
- Quaternary
- The geological period covering about 2 million years ago to the present.
- Rhyolite
- Volcanic rock that characteristically is light in colour, contains 69% silica or more, and is rich in potassium and sodium.
- Richter Scale
- A measure of the magnitude of an earthquake at its epicentre. Each point increase on the Richter scale is a 30 times increase in the magnitude.
- Seismograph
- An instrument for detecting and recording the intensity, direction, and duration of a movement of the ground caused by an earthquake or explosion.
- Shield Volcano
- A gently sloping volcano in the shape of a flattened dome and built almost exclusively of gentle lava flows.
- Silurian
- The geological period from 439 million to 409 million years ago.
- Soil Bulk Electrical Conductivity
- Conductivity of electricity through soil.
- Soil Heat Flux
- The amount of heat flowing into a cross-sectional area of soil per unit time.
- Soil Volumetric Water Content
- The proportion of a volume of soil that is water.
- Spring
- Occurs at the intersection of the water table with the ground surface.
- Stalactite
- A cone shaped deposit of minerals hanging from the roof of a cavern.
- Stalagmite
- A post of dripstone growing up from a cave floor.
- Stratovolcano
- A steep volcanic cone built by both lava flows and airborne rocks and ash.
- Strombolian Eruption
- A type of volcanic eruption characterized by jetting of clots or fountains of fluid basaltic lava from a central crater.
- Sylvine
- Naturally occuring potassium chloride.
- Tensile Fracture
- A fracture caused by tensional stress.
- Tephra
- Materials of all types and sizes that are erupted from a crater or volcanic vent and deposited from the air.
- Tertiary
- The geological period from 65 million to 1.64 million years ago.
- Thermal Spring
- A spring whose temperature is 6.5°C or more above mean annual air temperature.
- Triassic
- The geological period from 245 million to 208 million years ago.
- True Meridian
- A great circle through the geographical poles.
- Tsunami
- A giant wave set in motion by a large earthquake under or near the ocean that causes the ocean floor to shift vertically.
- Volcanic Ash
- Lava from a volcano that is in the form of chunks smaller than an apple, about the size of marbles.
- Volcanic Bomb
- A large lump of lava thrown out of a volcano during an eruption.
- Volcanic Dust
- Lava in the form of small, tiny particles thrown from a volcano during an eruption.
- Volcanoes
- Vents or fissures in the earth's crust through which gases, molten rock, or lava , and solid fragments are discharged.
