2. What is Dolerite?
A dolerite is the medium-grained equivalent of a
basalt - a basic rock dominated by plagioclase
and pyroxene.
3. Other Names for 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.
• Microgabbro
5. Where it is found:
It's a medium-grained igneous rock usually found
in shallow level intrusions like dykes, sills,
or volcanic plugs.
6. What does it contain?
• It contains largely plagioclase feldspar,
pyroxene, and augite, with labradorite and
titanaugite as additional "essential" minerals.
• Magnetite, titano-magnetite, and ilmenite can
occur as secondary or "accessory" minerals
7. • It will sometimes have olivine, at which point it's
called an "olivine dolerite".
• In other cases, quartz can occur in sufficient
quantity to call it... a "quartz dolerite."
8.
9. Texture
• It has normally has a fine, but visible texture of
euhedral lath-shaped plagioclase crystals (62%)
set in a finer matrix of clinopyroxene, typically
augite (20–29%), with minor olivine (3% up to
12% in olivine diabase), magnetite (2%), and
ilmenite (2%).
• The texture is termed “diabasic” and is typical
of diabases. This diabasic texture is also termed
“interstitial”
10. Occurrence:
• Dolerite is usually found in smaller relatively
shallow intrusive bodies such as dikes and sills.
• Dolerite dikes occur in regions of crustal
extension and often occur in dike swarms of
hundreds of individual dikes or sills radiating
from a single volcanic center.
11. Alteration
• Plagioclase is converted to sassurite.
• Sericitization is a process of mineral alteration caused
by hydrothermal fluids invading permeable country
rock. Plagioclase feldspar within the rock is converted
to the mineral sericite.
• Pyroxene to hornblende, actinolite, or chlorite.
• Olivine is altered to serpentine and magnetite.
12. Weathering
• As dolerite cooled and solidified after its molten
intrusion, joints formed, approximately at right
angles to one another.
• Due to rectangular jointing pattern it usually
shows spheroidal weathering.
• Round Cobbles may show “onion skin
weathering”.
