Is dolerite an intrusive rock?
Dolerite is the medium grained, intrusive, equivalent of a basalt (link to basalts). It usually occurs as dykes, plugs or sills. Being intruded into country rocks at shallow levels, the magma has more time to cool than if extruded.
What is meant by igneous intrusion?
An intrusion is a body of igneous (created under intense heat) rock that has crystallized from molten magma. Low-density magmas (such as granitic magmas) are more buoyant in their invasions and cause subsidence of the surrounding wallrocks.
What is dolerite in geology?
Dolerite is the medium-grained equivalent of gabbro. The crystals are slightly smaller than gabbro, indicating that the magma cooled more quickly. It usually occurs as small intrusions called ‘dykes’ or ‘sills’ which are sheet-like and cut through the surrounding rocks.
What is intrusions in the rock?
An intrusion is any body of intrusive igneous rock, formed from magma that cools and solidifies within the crust of the planet. In contrast, an extrusion consists of extrusive rock, formed above the surface of the crust.
What are dolerite igneous rocks?
Diabase (dolerite) is a dark-colored igneous rock. It is compositionally equivalent to gabbro and basalt but texturally between them. Diabase is a common rock type. It occurs mostly in shallow intrusions (dikes and sills) of basaltic composition. The term “microgabbro” is sometimes used to refer to such rocks.
What type of igneous rock is dolerite?
diabase, also called Dolerite, fine- to medium-grained, dark gray to black intrusive igneous rock. It is extremely hard and tough and is commonly quarried for crushed stone, under the name of trap.
What type of intrusion is igneous?
Igneous intrusions form when magma cools and solidifies before it reaches the surface. Three common types of intrusion are sills, dykes, and batholiths (see image below).
What are the properties of dolerite?
Dolerite. Fine grained, ophitic texture. Primary minerals – plagioclase, pyroxene, hornblende and quartz. Acicular and lath-like plagioclase, equant grains of pyroxene – some alteration to chlorite along cleavage and fissures.
What are types of intrusions?
Three common types of intrusion are sills, dykes, and batholiths (see image below).
Where are igneous intrusions found?
Intrusions have a wide variety of forms and compositions, illustrated by examples like the Palisades Sill of New York and New Jersey; the Henry Mountains of Utah; the Bushveld Igneous Complex of South Africa; Shiprock in New Mexico; the Ardnamurchan intrusion in Scotland; and the Sierra Nevada Batholith of California.
What type of stone is dolerite?
Dolerite is the name given to the medium-grained intrusive basic igneous rock commonly found in dykes and sills; in North America and continental Europe it is often referred to as diabase, but many authors restrict this term to altered dolerite.
What are the characteristics of a dolerite?
Dolerite is relatively poor in silicon and rich in minerals, and after chemical weathering doleritic soils have high clay contents. Despite the high temperatures of the igneous intrusion, carbon has been preserved at the dolerite-shale contact and in shale enclaves where partial melting of the shale has occurred.
What is the Oenpelli dolerite intrusive event?
A geological event known as the Oenpelli Dolerite intrusive event occurred about 1,720 million years ago in western Arnhem Land, in the Northern Territory, creating curved ridges of Oenpelli Dolerite stretching over 30,000 square kilometres (12,000 sq mi).
When did dolerite first appear?
The dolerite is believed to have existed as much as 1/2 billion years before the meteorite impact. This example is from Wikipedia and may be reused under a CC BY-SA license. The pebbles are mostly quartzite, but include dolerite and agate. This example is from Wikipedia and may be reused under a CC BY-SA license.
What is the difference between dolerite sills and laccoliths?
The dolerite sills of the Karoo South Africa, the Transantarctic mountains and Tasmania occur as undulating discordant sheets. Laccoliths are lens-shaped intrusions where magmas were emplaced like a sill between sedimentary layers but then bulged up into a dome. This commonly happens in dioritic intrusions.