-
Gabbro in Oceanic Crust
It is often stated that Earth’s oceanic crust is made up of basalt. The word “basalt” is used because the rocks of the oceanic crust have a “basaltic” composition. However, only a thin surface veneer of oceanic crust is basalt. The deeper rocks of the oceanic crust are generally coarser-grained gabbro. Basalt occurs at the…
-
Gabbro and Basalt are Related
Gabbros are equivalent in composition to basalts. The difference between the two rock types is their grain size. Basalts are extrusive igneous rocks that cool quickly and have fine-grained crystals. Gabbros are intrusive igneous rocks that cool slowly and have coarse-grained crystals.
-
What Minerals are in Gabbro?
Gabbro is composed mainly of calcium-rich plagioclase feldspar (usually labradorite or bytownite) and pyroxenes (usually augite). Minor amounts of olivine might also be present in the rock. (See composition chart on this page.) This mineral composition usually gives gabbro a black to very dark green color. A minor amount of light-colored mineral grains may also be present. Unlike many other igneous rocks, gabbro…
-
What is Gabbro?
Gabbro is a coarse-grained, dark-colored, intrusive igneous rock. It is usually black or dark green in color and composed mainly of the minerals plagioclase and augite. It is the most abundant rock in the deep oceanic crust. Gabbro has a variety of uses in the construction industry. It is used for everything from crushed stone base materials at construction…
-
Diorite in Art
Diorite is difficult to sculpt because of its hardness, variable composition, and coarse grain size. For those reasons, it is not a favored stone of sculptors, although it was popular among ancient sculptors of the Middle East. The most famous diorite sculpture is the Code of Hammurabi, a black diorite pillar about seven feet tall,…
-
Uses of Diorite
In areas where diorite occurs near the surface, it is sometimes mined for use as a crushed stone. It has a durability that compares favorably to granite and trap rock. It is used as a base material in the construction of roads, buildings, and parking areas. It is also used as a drainage stone and for erosion…
-
Diorite and Andesite
Diorite and andesite are similar rocks. They have the same mineral composition and occur in the same geographic areas. The differences are in their grain sizes and their rates of cooling. Diorite crystallized slowly within the Earth. That slow cooling produced a coarse grain size. Andesite forms when a similar magma crystallizes quickly at Earth’s surface. That rapid cooling produces…
-
What is Diorite?
Diorite is the name used for a group of coarse-grained igneous rocks with a composition between that of granite and basalt. It usually occurs as large intrusions, dikes, and sills within continental crust. These often form above a convergent plate boundary where an oceanic plate subducts beneath a continental plate. Partial melting of the oceanic plate produces a basaltic magma that…
-
Uses of Diabase
Most diabase that is mined is used in the construction industry. There are several types of use: 1) Crushed Stone: Diabase is one of many types of “trap rock” used as crushed stone in the construction industry. These are durable rocks that have many uses. For most of these uses, the aggregate must meet certain specifications of abrasion…
-
Geologic Occurrence of Diabase
The formation of diabase has two requirements: 1) a basaltic magma source 2) shallow emplacement and cooling in a relatively small subsurface structure such as a sill, dike, lopolith or laccolith.