• 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.

• Vertical Triassic diabase cross-cutting Jura-Triassic sedimentary strata

• Note dike offset

A view of the dolerite dyke cutting through the granite.

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