This glossary may be incomplete but will be added to from time to time.
Aa - Used in reference to a basaltic lava that occurs in flows with a fissured, rough, jagged and sometimes frothy surface. A term of Hawaiian origin. Compare with Pahoehoe.
Aquiclude - A formation or bed that is impermeable and acts as a barrier to the flow of groundwater.
Aquifer - Formations saturated with water capable of yielding that water in usable quantities
Aquitard - A formation or bed of low permeability adjacent to an aquifer. Often contains finer grained sediments or rock with low low connectivity of void spaces. However, it may serve as a storage unit for ground water though it is difficult to extract water from.
Andesite - An intermediate (moderate silica) extrusive (volcanic) rock usually dark grey in colour. Andesites often form lava flows or volcanic ash deposits formed in moderately violent eruptions. Minerals that make up andesite may includes quartz, feldspars and micas and may include other minerals such as pyroxenes. The intrusive (plutonic) equivalent of andesite is diorite.
Anticline - A structure where rock strata/layers slope downwards away from a fold hinge/crest. See also Syncline
Basalt - A mafic (moderate to low silica) extrusive (volcanic) rock usually dark in colour. Basalts often form lava flows that can cover large areas. Minerals that make up basalt include feldspars and may include olivine, quartz, pyroxenes, micas and other minerals depending on chemistry of the rock. The intrusive (plutonic) equivalent of basalt is gabbro. There are two main series of basalt rocks, tholeiitic and calc-alkaline.
Batholith - A large body of intrusive igneous rock that may be a single very large pluton or made from a group of plutons. In the case of the New England Batholith there are numerous intrusions of granite type rocks which were emplaced during a series of related tectonic events.
Caldera - A volcanic feature from the collapse of the land around a volcano following an eruption. The eruption drains the underlying magma chamber leading to subsidence of the land in the central area of the volcano.
Cenozoic Era - Sometimes spelled Cainozoic. This is a period of time that extends to 66.5 million years until the present. The Cenozoic can be divided into the Paleogene, Neogene and Quaternary periods.
Cirque -a landscape feature that is semicircular or crescent-shaped basin with steep sides and a gently sloping floor formed in mountainous regions by the action of ice.
Dolomite - An impure limestone. Where limestone is composed almost entirely of calcium carbonate, dolomite contains a large proportion of magnesium meaning the chemistry is a magnesium and calcium carbonate. Often dolomite can be distinguished from normal limestone buy its colour.
Dyke - An intrusive igneous body with its thickness often much smaller than its height and length. A dykes thickness can vary from centimetre scale to many metres and the lateral dimensions can extend over many kilometres. A dike is an intrusion into an opening cross-cutting fracture which pushes aside other rock and can cause some degree of metamorphism depending on the temperature an side of emplacement. Dikes are usually near vertical in orientation during emplacement otherwise they are known as sills. Very large igneous bodies are called plutons.
Felsic - A silica over-saturated rock. This means that there is an abundance of quartz in the rock. Sometimes felsic rocks are referred to as acid but this does not actually refer to the pH acidity of the rock.
Granite - A felsic (high silica) intrusive (plutonic) rock usually light in colour. Granites often form over large areas and are called batholiths in this situation. Since these rocks were formed underground they are evidence of a significant change in the terrain. When they were formed they may have been associated with volcanoes that have since been weathered and eroded away. Minerals that make up granite may include quartz, feldspars and may include micas and other minerals depending on the chemistry of the rock. The extrusive (volcanic) equivalent of granite is rhyolite.
Granophyre - A fine grained felsic intrusive. A granitic rock having a fine grained groundmass with larger feldspar and quartz crystals, i.e. a porphyritic texture.
Groundwater - Water contained within rock, sediment or soil below the ground's surface. Although the terms are often used interchangeably, groundwater can be but not always an aquifer.
Lithic - comprised of other pieces of rock.
For example sandstones often contain small fragments of other rocks from
which the sandstone is partially or completely derived.
Mafic - A silica saturated to under-saturated rock. This means that there is usually no quartz crystals in the rock. Sometimes mafic rocks are referred to as alkaline but this soes not refer to the pH acidity of the rock.
Migmatite - A composite silicate metamorphic rock with distinctly different parts. These parts are typically consists of darker and lighter parts. The darker parts usually exhibit features of metamorphic rocks whereas the lighter parts are of igneous-looking appearance.
Monazite - A rare earth and phosphate mineral with chemical formula (Ce,La,Y,Th)PO4 . Usually reddish brown in colour and radioactive. It is also very resistant to weathering.
Moraine - An accumulation of material deposited by glaciers. These accumulations tend to be made up of different sized particles deposited in moraines, ranging from fine silt to large boulders. The sediment and rock material in moraines also tend to have angular edges.
Orocline - An orogenic belt with a change in horizontal direction, either a horizontal curvature or a sharp bend. It is also sometimes referred to as a geoflex. The processes that lead to an orocline are in a different plain of stress to those that cause folding.
Orogen - Essentially an area formed from folding and thrusting of the crust usually forming a mountainous terrain. The actual process is called orogenesis and is associated with compressional tectonic environments such as continental collision or subduction zones.
Pahoehoe - Used in reference to a basaltic lava that forms smooth lava flow surfaces. The surface of the lava flow shows a characteristic 'ropey' appearance. The other type of lava flow which is much rougher in appearance is called aa.
Paleosol - A preserved soil profile often preserved between flows of lava or covered by a layer of sediment preserving the historical weathering profile.
Periglacial - Periglacial features are the product of low temperatures, frequent frosts and persistent snow with alternation of freezing and thawing. Periglaciation causes the mass movement of water-saturated soil and stones downslope over frozen subsoil. Periglacial features include terracing, soil movement, shattered boulders and rock rivers.
Pluton - An intrusion of molten rock that has been emplaced into the Earths crust. Gabbro and granite are examples. Plutons can the source for volcanic (extrusive) rocks.
Ptygmatic folding - Contorted and folded granitic veins which characteristically occur in migmatites. However, the term is now used more widely to describe a form of folding where single isolated layers of relatively high competence material are enclosed in a matrix of lower competence and strongly shortened.
Rhyolite - A felsic (high silica) extrusive (volcanic) rock usually light in colour. Rhyolites often form thick lava flows or volcanic ash and glass deposits formed in violent eruptions. Minerals that make up rhyolite may include quartz, feldspars and may include micas and other minerals depending on the chemistry of the rock. The intrusive (plutonic) equivalent of rhyolite is granite.
Solifluction - the slow downhill movement of soil saturated with meltwater over a permanently frozen subsoil (permafrost) in tundra regions.
Syncline - A structure where rock strata/layers slope upwards away from a fold hinge/trough. See also Anticline.
Tertiary - A period of time encompassing a portion of the Paleogene and Neogene periods which are part of the Cenozoic era. The Tertiary is followed by the Quaternary period. The term Tertiary is in common use in Australia but is uncommon elsewhere. The International Stratigraphic Commission does not recognise the Tertiary and in Australia its use is still considered informal but none the less is in widespread use.
Tholeiitic - one of two significant series of volcanic rocks. In tholeiitic rocks the primary melt is iron depleted relative to the calc-alkaline series (the other significant series), as such the minerals become more and more magnesium rich as iron is used up in the earlier crystals to form. They also tend to be depleted in sodium and potassium. Tholeiitic rocks are commonly basaltic but as the magma matures can become andesitic or even rhyolitic. Tholeiites are best identified using petrographic or geochemical techniques.
Tor - A large, free-standing rock outcrop that rises abruptly from the surrounding smooth and gentle slopes of a rounded hill summit or ridge crest.
Tuff - a volcanic rock formed from the compaction of volcanic ash and glass, but sometimes showing larger, usually angular particles of sand size or bigger. Tuff is formed during explosive eruptions which eject large amounts of materials into the air.
Ultramafic - Sometimes referred to as ultrabasic refers to the silica content of the rock. In ultramafic rocks there is very little silica (usually less than 45%) such that the common rock forming mineral of quartz is not present and feldspars are less common being replaced by the mineral group feldspathoids. These rocks are often rich in magnesium and iron.
Nonconformity - refers to a surface between two layers, usually sedimentary layers, that shows a period of erosion or non-deposition between the two layers. The nonconformity represents a time gap between the deposition of the two layers. see also disconformity.
Volcano (Central Volcano) - A volcano constructed by the eruption of pyroclastics, volcanic bombs and other debris as well as lava flows from a central point, making a more or less cone shaped peak. Strato-Volcanoes and Shield-Volcanoes are good examples. See also Volcanic Province
Watershed - The line that defines the ridge that separates different catchments from each other. For example the much of the Great Dividing Range defines the watershed from the coastal catchments from those of the Murray-Darling Basin. Note that in the United States, this term is used to refer to a catchment itself.
