Dolerite
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Transcript of Dolerite
• Introduction
• Mineralogy
• Textures
• Classification of dolerite
• Dolerite dyke
• Formation of dolerite
• Distribution
• Uses
• Conclusion
• Reference
• A dolerite is the medium-grained equivalent of a basalt - a basic rock dominated by plagioclase and pyroxene.
• Dolerites also often include olivine or quartz and can be alkali basalts, olivine tholeiites or quartz tholeiites. They can contain a wide range of accessory minerals including hornblende and biotite. Dolerites usually have an ophitic texture
• Dolerite is typically found as a hypabyssal igneous rock, typically within dykes. Dykes may also contain basalt instead of dolerite.
• Diabase is often used as a synonym of dolerite by american geologists, however, in europe the term is usually only applied to altered dolerites.
Mineralogy: Phenocrysts comprise olivine (olivine diabase) and/or pyroxene or plagioclase. The groundmass comprises the same minerals with iron oxide, and sometimes with some quartz, hornblende or biotite.
• Ophitic texture - laths of plagioclase in a coarse grained matrix of pyroxene crystals, where in the plagioclase is totally surrounded by pyroxene grains. This texture is common in diabases and gabbros.
• Subophitic texture - similar to ophitic texture where in the plagioclase grains are not completely enclosed in a matrix of pyroxene grains.
• Pyroxene and calcic plagioclase,typically labradorite ,as essential constituents,with or without some olivine and a variable amount of interstitial residum consisting of alkali feldspar and quartz, often intergrowth .
• The accessory constituents are iron-ore and apatite with ,in some a little hornblende or biotite.
• Single lime-rich more or less titaniferous augite as their pyroxene.
• They normally have olivine as a further essential constituent and not infrequently have a little interstitial analcite.
• They may be illustrated by those occurring in Tertiary igneous province of scotland.
Sam Edwards on the first ascent of Slap Dancer (26, 5.12b), a dolerite pillar in the Organ Pipes, Tasmania, Australia
Formation of Formation of doleritedoleriteDolerite cools under basaltic volcanoes, like those at mid-ocean ridges. It cools moderately quickly when magma moves up into fractures and weak zones below a volcano. There, it forms dikes (tabular igneous rock bodies that cut across pre-existing rock layers or bodies) or sills(tabular igneous rock bodies that form parallel to pre-existing rock layers). The moderate cooling rate allows small visible crystals to form in the rock.
Distribution
• Tholeiitic dolerite - occur in karroo of South Africa and those of Tasmania and Antartica were intruded.
• Alkali dolerites - occur in Scotland particularly in where they may form large sills. Midlands of England, as at Rowley Regis, near Birmingham; in the Clee hills, Shropshire and Derbyshire.
In geological timescale this Karoo dolerite intruded approximately 83 million years ago during the Mesozoic era
• Dolerite are used in monumental masonry,building material,concrete aggregate, paving stone, road stone, road stones and ornamental stones.
UsesUses
ConclusionConclusion• A dolerite is the medium-grained equivalent of a
basalt - a basic rock dominated by plagioclase and pyroxene.
• One of its distinguishing character is its ophitic texture.
• Dolerite is typically found as a hypabyssal igneous rock, typically within dykes, however, it may also occur in sills.
• Tholeiitic dolerite and alkali dolerite are the two types.
• Dr.S.R Nockolds, PETROLOGY PETROLOGY FORFOR STUDENTS,STUDENTS, Pp:120-135.
• Dietrich, R. and Skinner, B., 1979, Rocks , Rocks and Rock Mineralsand Rock Minerals, pg. 108.
• en.wikipedia.org/wiki/Diabase
• en.wikipedia.org/wiki/Quartz-dolerite