Dolerite is a medium-grained mafic igneous rock that is very similar to basalt. It typically has an ophitic texture and is composed mainly of plagioclase feldspar and pyroxene minerals. Dolerite commonly forms as hypabyssal intrusions in dykes and sills and is found worldwide, including locations in South Africa, Tasmania, and Scotland. Dolerite has various industrial uses as a construction material.

1. DOLERITE

2. • Introduction
• Mineralogy
• Textures
• Classification of dolerite
• Dolerite dyke
• Formation of dolerite
• Distribution
• Uses
• Conclusion

3. • 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

4. • 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.

5. 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.

6. • 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.

9. • 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.

10. • 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.

11. • Vertical Triassic
diabase cross-
cutting Jura-
Triassic
sedimentary strata
• Note dike offset

12. A view of
the dolerite
dyke cutting
through the
granite.

13. Sam Edwards on
the first ascent of
Slap Dancer (26,
5.12b), a dolerite
pillar in the Organ
Pipes, Tasmania,
Australia

14. Formation of
dolerite
Dolerite 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.

15. 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.

16. In geological timescale this Karoo dolerite intruded
approximately 83 million years ago during the
Mesozoic era

17. • Dolerite are used in monumental
masonry,building material,concrete
aggregate, paving stone, road stone, road
stones and ornamental stones.
Uses

18. Conclusion
• 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.

19. • Dr.S.R Nockolds, PETROLOGY FOR
STUDENTS, Pp:120-135.
• Dietrich, R. and Skinner, B., 1979, Rocks
and Rock Minerals, pg. 108.
en.wikipedia.org/wiki/Diabase
•
• en.wikipedia.org/wiki/Quartz-dolerite