Phaneritic means that diorite contains crystals that are large enough to see with the naked eye. Diorite texture will often depend on the grain sizes available in the rock.
Typically the texture will be fairly course unless diorite is smoothed out and polished. Diorite is formed by the mixing of magma containing basalt or gabbro, which has the iron and magnesium minerals in it, and magma that contains granite, which will have the feldspar minerals in it. This mixing of two magmas will create the intermediate composition that comprises diorite.
To finish it off, a little bit of crystallization underground will form what we know as diorite. The color of diorite will range in many different grays to black with white. Diorite is used in roads and pavement, as well as other structural building materials due to its durability. Diorite can also be used as a more cosmetic type of building stone that you might find in parks, curbs, or outside of buildings…. Part of that beautiful cosmetic look we commonly see with diorite is in the application of shinny polished countertops.
This helps avoid potential confusion in identifying the rock it was made from. Rhyolite is often pink or gray and has a glassy groundmass. This is a less typical white example. Being high in silica, rhyolite originates from a stiff lava and tends to have a banded appearance. Indeed, "rhyolite" means "flowstone" in Greek. This type of igneous rock is typically found in continental settings where magmas have incorporated granitic rocks from the crust as they rise from the mantle.
It tends to make lava domes when it erupts. Scoria, like pumice, is a lightweight extrusive rock. This type of igneous rock has large, distinct gas bubbles and a darker color. Another name for scoria is volcanic cinders, and the landscaping product commonly called "lava rock" is scoria — as is the cinder mix widely used on running tracks.
Scoria is more often a product of basaltic, low-silica lavas than of felsic, high-silica lavas. This is because basalt is usually more fluid than felsite, allowing bubbles to grow larger before the rock freezes. Scoria often forms as a frothy crust on lava flows that crumble off as the flow moves.
It also is blown out of the crater during eruptions. Unlike pumice, scoria usually has broken, connected bubbles and does not float in water. This example of scoria is from a cinder cone in northeastern California at the edge of the Cascade Range.
Syenite is a plutonic rock consisting chiefly of potassium feldspar with a subordinate amount of plagioclase feldspar and little or no quartz. The dark, mafic minerals in syenite tend to be amphibole minerals like hornblende. Being a plutonic rock, syenite has large crystals from its slow, underground cooling. An extrusive rock of the same composition as syenite is called trachyte.
Syenite is an ancient name derived from the city of Syene now Aswan in Egypt, where a distinctive local stone was used for many of the monuments there. However, the stone of Syene is not a syenite, but rather a dark granite or granodiorite with conspicuous reddish feldspar phenocrysts.
Tonalite is a widespread but uncommon plutonic rock, a granitoid without alkali feldspar that may also be called plagiogranite and trondjhemite. The granitoids all center around granite, a fairly equal mixture of quartz, alkali feldspar, and plagioclase feldspar. Recognizing tonalite takes a close look with a magnifier to be sure that alkali feldspar is truly absent and quartz is abundant. Most tonalite also has abundant dark minerals, but this example is almost white leucocratic , making it a plagiogranite.
Trondhjemite is a plagiogranite whose dark mineral is biotite. This specimen's dark mineral is pyroxene, so it's plain old tonalite. An extrusive rock with the composition of tonalite is classified as dacite. Tonalite gets its name from the Tonales Pass in the Italian Alps, near Monte Adamello, where it was first described along with quartz monzonite once known as adamellite. Troctolite is a variety of gabbro consisting of plagioclase and olivine without pyroxene. Different blends in the basic gabbroid mix have their own special names, and troctolite is the one in which olivine dominates the dark minerals.
The pyroxene-dominated gabbroids are either true gabbro or norite, depending on whether the pyroxene is clino- or orthopyroxene. The gray-white bands are plagioclase with isolated dark-green olivine crystals. The darker bands are mostly olivine with a little pyroxene and magnetite. Around the edges, the olivine has weathered to a dull orange-brown color.
Troctolite typically has a speckled look, and it's also known as troutstone or the German equivalent, forellenstein. This specimen is from the Stokes Mountain pluton in the southern Sierra Nevada and is about million years old. Tuff is technically a sedimentary rock formed by the accumulation of volcanic ash plus pumice or scoria. Tuff is so closely associated with volcanism that it is usually discussed along with types of igneous rocks.
Tuff tends to form when erupting lavas are stiff and high in silica, which holds the volcanic gases in bubbles rather than letting them escape. The brittle lava is readily shattered into jagged pieces, collectively called tephra TEFF-ra or volcanic ash. Fallen tephra may be reworked by rainfall and streams. Tuff is a rock of great variety and tells the geologist a lot about conditions during the eruptions that gave birth to it.
If tuff beds are thick enough or hot enough, they can consolidate into a fairly strong rock. The city of Rome's buildings, both ancient and modern, are commonly made of tuff blocks from the local bedrock. In other places, tuff may be fragile and must be carefully compacted before buildings can be constructed with it.
Residential and suburban buildings that shortchange this step remain prone to landslides and washouts, whether from heavy rainfall or from the inevitable earthquakes. Actively scan device characteristics for identification.
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Share Flipboard Email. An igneous rock formed by subterranean crystallized magma, Diorite is composed of plagioclase feldspar, quartz, hornblende, pyroxene and biotite. Varieties that lack hornblende are referred to as "leucodiorite".
The color of diorite varies from grey to dark grey to black, speckled with lighter colors that may appear white. Diorite might contain small amounts of apatite, ilmenite, microcline, and other minerals. It has a coarse, grainy structure, wherein its large grains are arranged in an interlinked pattern. The density of this rock is between 2. It is easily recognized by geologists by virtue of its unique texture, and its "salt and pepper" appearance in terms of coloration.
Diorite deposits are relatively rare, and most commonly occur as sills, dikes, or stocks, or in the form of large masses as batholiths, and are often associated with coinciding with gabbro and granite deposits. It is about 19 inches tall and is currently displayed at the Metropolitan Museum of Art. A public domain image. The vase on the right was made in ancient Egypt from diorite with spectacular feldspar phenocrysts.
It is in the collection of the Field Museum. 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, inscribed with Babylonian laws in about BC. Diorite has the ability to accept a bright polish, and it has occasionally been cut into cabochons or used as a gemstone. In Australia, a diorite with beautiful pink feldspar phenocrysts has been cut into cabochons and called "pink marshmallow stone. The best way to learn about rocks is to have specimens available for testing and examination.
Diorite Cabochon: A diorite in Australia contains large, beautiful pink feldspar crystals. It is often cut into cabochons for use as a novelty gem. It has been given the name "pink marshmallow stone. Find Other Topics on Geology.
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