How was dolerite formed?
Dolerite is an igneous rock, that is, rock initially molten and injected as a fluid into older sedimentary rocks. The magma, of quartz tholeiite composition, was emplaced as a liquid which rose upwards through the basement rocks into older sedimentary rocks of the Parmeener Supergroup.
What kind of rock is formed when magma?
Extrusive, or volcanic, igneous rock is produced when magma exits and cools above (or very near) the Earth’s surface. These are the rocks that form at erupting volcanoes and oozing fissures.
How is diorite formed?
How did it form? Diorite is a course-grained igneous rock that forms when magma rich in silica cools slowly deep within the Earth’s crust.
Where can dolerite be found?
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 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 is interesting about the diabase’s environment of formation?
1) The plagioclase in diabase is often of the labradorite variety. Diabase from some quarries contains abundant crystals of labradorite that are capable of producing colorful reflections known as “labradorescence”. When cut and polished, this diabase can serve as an attractive architectural stone.
What rocks are made from lava?
The two main categories of igneous rocks are extrusive and intrusive. Extrusive rocks are formed on the surface of the Earth from lava, which is magma that has emerged from underground. Intrusive rocks are formed from magma that cools and solidifies within the crust of the planet.
What type of magma makes diorite?
There, the basaltic magma mixes with granitic magmas or melts granitic rock as it ascends through the continental plate. This produces a melt that is intermediate in composition between basalt and granite. Diorite forms if this type of melt crystallizes below the surface.
What metamorphic rock is formed from diorite?
Diorite – Medium-grained hornblende diorite metamorphosed in part to amphibolite and hornblende gneiss. Diorite and gabbro – Complex of diorite and gabbro, subordinate metavolcanic rocks and intrusive granite and granodiorite.
What is dolerite in geology?
Is dolerite plutonic rock?
Igneous rocks which form at shallow depths in the earth are known as hypabyssal rocks. They generally have smaller crystals. Examples of hyabyssal rocks include dolerite, microgranite and microdiorite. Igneous rocks which cool and solidify deep in the earths crust are called plutonic rocks.
What is a dolerite rock?
Dolerite is the medium grained, intrusive, equivalent of a basalt (link to basalts). It usually occurs as dykes, plugs or sills.
How are phenocrysts formed in dolerite?
The large crystals, called phenocrysts, in dolerite are feldspar crystals that grew as the magma cooled slowly deep in a magma chamber. Later the magma with the large phenocrysts moved upward quickly, causing more rapid cooling of the rest of the magma and the formation of the small crystals that make up the rest of the rock.
Why are there different sizes of crystals in dolerite?
The different crystal sizes are the result of different rates of cooling as the magma body moved upward. The large crystals, called phenocrysts, in dolerite are feldspar crystals that grew as the magma cooled slowly deep in a magma chamber.
What is a dolerite sill?
As the magma cooled it produced a hard, black rock (not unlike the basalt lavas) that is called dolerite. Where the magma invaded a horizontal bedding plane we call it a sill. Being much harder than the under- and over-lying sandstones and shales, these dolerite sills form the flat-topped hills so distinctive of the Karoo scenery in South Africa.