pillow lavas

hot, fluid magma rapidly cooled into pillow structures when coming into the sea or water saturated sediments.


pillow structures

spherical or ellipsoidal structures usually composed of basaltic lava, generally about 1m in diameter. These are the result of the rapid cooling of hot, fluid magma that comes into the sea or into water saturated sediments.



one of a group of extrusive rocks (those extruded at the Earth's surface) commonly showing flow texture, and typically porphyritic, with phenocrysts of quartz and potassium feldspar in a glassy to microcrystalline groundmass. Rhyolite is the extrusive equivalent of granite.



a zone where two tectonic plates are pulling apart, often forming a mid-ocean ridge with the associated upwelling of hot magma.



a yellow, red, brown or black tetragonal mineral, TiO2, an important ore of titanium. Rutile occurs as a very common accessory mineral in intrusive igneous rocks, or dispersed through quartz veins.



a sedimentary rock composed of sand-sized grains in a matrix of clay or silt, and bound together by a cement that may be carbonate. Quartz forms about 65% of the detrital fraction of the average sandstone, and feldspars about 10 to 15%. Most sandstones originate as underwater deposits, usually marine; many sandstones were originally beach deposits.


sea level

the level corresponding to the surface of the sea half way between mean low and high tide.


sedimentary rocks

rocks formed by the consolidation of sediment settled out of water, ice or air and accumulated on the Earth's surface, either on dry land or under water. Sediments are consolidated into a rock mass by lithification. Sedimentary rock is typically stratified or bedded, beds can vary greatly in thickness.



fine-grained sedimentary rock formed by the compaction of silt, clay, or sand that accumulates in deltas and on lake and ocean bottoms. It is the most abundant of all sedimentary rocks. Shales may be black, red, grey or brown.



a tabular igneous intrusion with boundaries conformable with the planar structure of the surrounding rock.



a detrital particle, finer than very fine sand and coarser than clay, in the range of 0.004 to 0.062mm.


Sources Consulted:
Farndon, J. (1998). Concise Encyclopedia Earth, Dorling Kindersley, Great Britain, 192.
Lapidus, D.F. (1987) Collins Dictionary of Geology, Winstanley, I. (Ed.), HarperCollins, Great Britain, 565pp.

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