The best way to learn about rocks is to have specimens available for testing and examination. The word \"basalt\" is used because the rocks of the oceanic crust have a \"basaltic\" composition. It is often stated that Earth's oceanic crust is made up of basalt. Gabbro can be polished to a brilliant black luster. The term itself comes from Italy. (after Le Maitre, 2005) Once you have determined the mineral assemblage of a rock, you can use the appropriate (intrusive or extrusive) QAPF chart to name it (fig. Width of sample 12 cm. Basalt occurs at the surface of the crust because the rocks there have cooled quickly. It means that it formed as magma cooled slowly in the crust. The area shown in this image is about 1/2 inch across. This means it's formed through the cooling and solidification of magma or lava. How do you know? products. Basalts are extrusive igneous rocks that cool quickly and have fine-grained crystals. Plagioclase is sodium-calcium feldspar. Anorthosite and troctolite are similar rocks also. Gabbro is a dark-colored coarse-grained intrusive igneous rock. Notice the large grains of pink, white, and gray minerals. The molten rock will crystalize and solidify giving the two basic groups of igneous rocks called Intrusive, formed under the earth, and Extrusive, formed above the earth. It contains more calcium than sodium in gabbro. Norite may be very similar to gabbro but contains orthopyroxene, not clinopyroxene. The specimen shown above is about two inches (five centimeters) across. A sample from La Palma. Most of the time, what is sold as black Granite is gabbro, another intrusive rock that doesn’t have the same composition or qualities of Granite. only a thin surface veneer of oceanic crust is basalt. “Gabbro” in the strict sense of the term is an intrusive rock that is chiefly composed of monoclinic pyroxene (clinopyroxene, abbreviated Cpx) and plagioclase. Plagioclase is striped black-gray-white, pyroxene is colorful, there are some small olivine grains as well. Close-up view of gabbro: Magnified view of the gabbro shown in the photograph at the top of the page. The difference between the two rock types is their grain size. make cemetery markers, kitchen counter tops, floor tiles, facing stone, and other dimension stone Gabbros are equivalent in composition to basalts. Anorthosite is almost monomineralic plagioclase-rock. Andesite is an extrusive volcanic rock with a composition that is intermediate between basalt and rhyolite. Gabbro is an intrusive igneous rock. 4a, b). The central cores of major mountain ranges consist of intrusive igneous rocks, usually granite. Leucocratic norite (orthopyroxene gabbro). Learn about teaching plate tectonics. (See composition chart on this page.). Rogaland, Norway. Unlike many other igneous rocks, gabbro usually contains very little quartz. Gabbroic rocks may contain small amounts of quartz (up to 5%). Napp, Flakstadøya, the Lofoten Archipelago, Norway. Formation Of Hypabyssal Rocks a sub category of the intrusive rock is the hypabyssal, or subvolcanic rock. Th… https://www.answers.com/Q/Is_gabbro_an_extrusive_or_intrusive_rock A light-colored intrusive or extrusive felsic rock, the shallow version of granite, is called felsite or rhyolite. When magma and lava cool and harden, they create igneous rocks. So why do we see the slowly-cooled intrusive version on the continents, but the rapidly-cooled extrusive basalt in the oceans? Width of sample 11 cm. Flakstadøya, the Lofoten Archipelago, Norway. what is the composition of an Gabro Sand rock? How does an igneous rock that has both large and small mineral crystals form? ... diorite, gabbro, granite, dacite, obsidian, pumice, pegmatite, peridotite, rhyolite, scoria, and tuff. Originally the rock was composed of plagioclase and pyroxene. When the magma solidifies within the earth's crust, it cools slowly forming coarse textured rocks, such as granite, gabbro, or diorite. It is normally coarse-grained, dark and typically contains feldspar, augite and sometimes olivine. In the same respect, granite is the cooled (and exposed) magma chamber for extrusive rhyolite. The key difference between intrusive and extrusive rocks is that the intrusive rocks are formed from magma whereas the extrusive rocks are formed from lava. Deep-seated intrusive rock gabbro is exposed there because of uplift and subsequent deep erosion. Gabbro is a coarse-grained and usually dark-colored igneous rock. The colors are frequently dark gray, black and green. Tangen, Norway. The difference between the two rock types is their grain size. This mineral composition usually gives gabbro a black to very dark green color. These two are the principal minerals in this rock. Olivine (weathered orange iddingsite in this sample) may be an important constituent in these rocks. Rhyolite is very closely related to granite. At greater depth the cooling rate is slower, and large crystals have time to develop. Width of sample 5 cm. Width of sample 8 cm. Pyroxene is almost exclusively clinopyroxene and norite is conversely rich in orthopyroxene. Basalt is the most common extrusive rock whil… Rock such as peridotite, which has low silica content and very high levels of iron and magnesium. The process of formation of rocks is different for various rocks. The source rock was probably gabbroic, but it has been severely altered to its current form which is composed of tremolite-actinolite series amphibole and framework silicate scapolite. Is gabbro an intrusive or extrusive igneous rock? Rocks form when mineral compounds react with heat, water or pressure. Gabbros are intrusive igneous rocks that cool slowly and have coarse-grained crystals. For instance, a dark-colored plutonic mafic rock, the deep version of basalt, is called gabbro. Plagioclase usually predominates over pyroxene. Other gabbros are mined to yield nickel, chromium, or platinum. In the dimension stone industry, gabbro is sold under the name "black granite." The classification scheme for gabbroic rocks without taking into account olivine and feldspathoids. What do you actually mean? Width of sample 13 cm. Igneous rocks with similar composition are basalt (extrusive equivalent of gabbro) and diabase (the same rock type could be named dolerite or microgabbro instead). Diorite is a coarse-grained, intrusive igneous rock that contains a mixture of feldspar, pyroxene, hornblende, and sometimes quartz. Pyroxenite and other ultramafic rocks are darker- and diorite is lighter-colored. A sample from Tangen, Hedmark, Norway. A minor amount of light-colored mineral grains may also be present. There are five types of intrusive rocks, which are granite, pegmatite, gabbro, diorite and peridotite. Granite is the most common type of land based intrusive rock, while gabbro is the type found most often underwater. Igneous rocks make up most of the rocks on Earth… Gabbro is an intrusive igneous rock that forms from the result of slow cooling of magma inside of a volcano. Gabbros are intrusive igneous rocks that cool slowly and have coarse-grained crystals. These rocks are formed because of the action of high pressure, high te… If there is more sodium in the plagioclase, then the rock type is named diorite. Extrusive igneous rocks are further divided into two major subcategories on the basis of the nature of the appearance of lavas on the earth’s surface e.g. Before discussing further differences between both rocks, let us see what is a rock and what are intrusive rocks and extrusive rocks. Width of sample 11 cm. It is the most abundant rock in the deep oceanic crust. Width of view 35 cm. It is often stated that Earth's oceanic crust is made up of basalt. Cpx is clinopyroxene, Opx is orthopyroxene, Plag is plagioclase. Rogaland, Norway. Yellow stripes in blue in the upper part of the image is an intergrowth of two pyroxenes (Opx in Cpx). Before we discuss the extrusive quality of basalt, it's important to understand that it's an igneous rock. The presence of sodium-rich feldspar, oligoclase or andesine, in contrast to calcium-rich plagioclase, labradorite or bytownite, is the main distinction between diorite and gabbro. Intense heat that liquefies inside the Earth makes hot molten material called magma. Gabbro with large augite phenocrysts embedded in white plagioclase. It is composed mostly of the mineral plagioclase feldspar with smaller amounts of pyroxene and olivine. Which of the following is an intrusive igneous rock and so will have large crystals? Gabbro sometimes contains economic amounts of some relatively rare metals. Diorite is an intrusive plutonic rock with a composition that is intermediate between gabbro and granite. Most of the earths surface is covered with rocks of various types. Preliminary QAPF classification of: a – intrusive rocks; b – extrusive rocks. 4.20), sill and plugs.Dolerite is heavy with specific gravity ranging between 2.9 and 3.3. Hornblende gabbro pegmatite. Gabbro is very similar to basalt in its mineral make up. A plutonis an igneous intrusive rock body that has cooled in the crust. and anywhere that a durable crushed stone is needed as fill. It is a highly desirable rock that stands up to weathering and wear. “Olivine” should be added to the rock name if it contains more than 10% of it. plagioclase often appear more. Gabbro is a dark-colored, coarse-grained intrusive igneous rock. Gabbro is composed mainly of calcium-rich plagioclase feldspar (usually labradorite or 4.19) intrusive equivalent of volcanic basalt or plutonic gabbro, and usually occurs as dykes (Fig. Gabbro is also used to make a number of rough-cut products such as curbing, ashlars, paving stones, and other products. 1. Slow cooling gives crystals a chance to grow. Intrusive Igneous Rocks. On the continents, gabbro can be found within thick lava flows of basaltic composition, where slow cooling allows large crystals to form. Igneous rock composition chart: A chart that illustrates the generalized mineral composition of igneous rocks. Hint: This Is One Of The Most Common Igneous Rocks Formed On Both Earth And The Moon. Tappeluft, Norway. bytownite) and pyroxenes (usually augite). The former was altered to scapolite and the latter to hornblende. Basalts are extrusive igneous rocks that cool quickly and have fine-grained crystals. Width of sample 11 cm. A hand sample from the Isle of Skye in Scotland (Black Cuillin Mountains). The classification scheme of olivine-bearing (>10%) gabbroic rocks. It is an intrusive rock. It is a small amount of olivine and amphibole. Troctolite contains mostly olivine and plagioclase, pyroxene again forms no more than 10% of the composition. Rock with two different-sized grains of the same mineral. So we can say that von Buch used the term roughly as we use it today. Extrusive Rocks. The difference between the two rock types is their grain size. Gabbro is a coarse-grained and usually dark-colored igneous rock. Intrusive igneous rocks have relatively large crystals that are easy to see. Igneous Rocks: A Classification and Glossary of Terms: Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks. Le Maitre, R. W. (2005). When magma cools within the Earth, the cooling proceeds slowly. Diorite is usually lighter in color and contains more amphiboles than pyroxenes. Gabrobro contains more calcium than sodium. Black granite: A view of polished gabbro (labradorite). In rapidly cooling magma, the resulting grains and crystals that form the rock are tiny in contrast to the larger grains and crystals found in rocks that cooled much slower deep in the crust. The most common use of gabbro is as a crushed stone or aggregate. Polished gabbro is sold under the name "black granite" and is used for cemetery markers, floor tile, kitchen counter tops, facing stone, and other dimension stone uses. The most important minerals in the gabbron are plagioclase and pyroxene. These colors are not real, they are caused by the interference between lightwaves. A few of the less common igneous rock types can be recognized by non-specialists. Width of sample 8 cm. Width of sample 7 cm. Intrusive, or plutonic, based upon the size of the crystals. They are similar because gabbro has the same composition as basalt, they are different because basalt is an extrusive igneous rock, gabbro is an intrusive igneous rock. Storås, Norway. If more than 95% of the pyroxene is Opx, then we have norite. This … (See illustration.). These rocks are composed of many distinct minerals. Dolerite and Diabase are both mafic igneous rocks having same mineralogical composition, but differ in formation. The word 'intrusive' indicates that it was formed beneath the surface of the earth. Rocks that contain less than 10% plagioclase are ultramafic (pyroxenite if pyroxenes are the dominant minerals). Ødegården Verk, Norway. Igneous Rocks: A Classification and Glossary of Terms: Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks, 2nd Edition. Igneous rocks are called intrusive when they cool and solidify beneath the surface. Cooling Rate: fast, extrusive; Intrusive Equivalent: gabbro; Other Characteristics: weathers to red-brown, hematite/limonite/clay mixture ANDESITE. … Depending on where and how the magma cools, igneous rocks are described as either intrusive or extrusive. Granite is a common intrusive rock. This rock was originally normal gabbro, but it has been metamorphosed by hot fluids that altered augite to similar but hydrated silicate mineral hornblende. Olivine And Py-roxene) And Plagioclase Would Be Classified As _____. These rocks are not as widespread as granitoids, but they are definitely not rare. Q. Intrusive igneous rocks cool slowly because they form underground. Gabbro is a coarse-grained, dark-colored, intrusive igneous rock that contains feldspar, pyroxene, and sometimes olivine. Basalt. Diorite, gabbro, anorthosite — the three root names in this field are separated according to the colour index and the average composition of their plagioclase – anortho… La Palma is an oceanic island which is largely composed of volcanic rocks. Granite is the most common intrusive igneous rock (see figure 2 for an example). Intrusive rocks form plutons and so are also called plutonic. It means that it formed as magma cooled slowly in the crust. Diallage is not defined as a mineral now, but it is monoclinic pyroxene anyway (either diopside or augite). In simple terms, gabbro is just the cooled magma chamber for the basaltic flows that erupt at the surface. Crushed gabbro is used as Gabbros are equivalent in composition to basalts. Slow cooling allows time for large crystals to form, so intrusive igneous rocks have visible crystals. Gabbro from the Troodos ophiolite in Cyprus. Gray is plagioclase, orange is weathered olivine (iddingsite). Igneous rocks with similar composition are basalt (extrusive equivalent of gabbro) and diabase (the same rock type could be named dolerite or microgabbro instead). Hornblende-scapolite (marialite) rock. Tappeluft, Norway. However, only a thin surface veneer of oceanic crust is basalt. Width of sample 10 cm. If there is more sodium in the plagioclase, then the rock type is called diorite. These rocks are all collectively called gabbroic rocks. Gabbro pegmatite from Cyprus (the Troodos ophiolite). Saussuritized version can be named metagabbro nowadays because its original composition has clearly been altered by metamorphism. If the magma forces its way to the surface, it is then called lava, which cools and hardens into extrusive rocks. If quartz makes up more than 20%, then the rock is one of granitoids1. Lava is magma that pushes up through the Earth's crust to the surface. We can tell the difference between intrusive and extrusive rock by noticing the texture of the rock surface. Brightly polished gabbro is used to It is an intrusive rock. This is the magma that did not break to the surface to cool as a basalt. Tremolite-scapolite rock. A pluton is an igneous rock body that forms within the crust. Gabbroic rock that contains almost no pyroxene is troctolite. Basalt is a common extrusive igneous rock formed by the rapid cooling of basaltic lava exposed at or very near the surface of Earth. With the insulation of the ground, the cooling process is a lot slowe… Basalt is the most significant representa­tive example of extrusive igneous rocks. Width of view 50 cm. Width of sample 55 mm. It is usually black or dark green in color and composed mainly of the minerals plagioclase and augite. Width of sample 11 cm. The word "basalt" is used because the rocks of the oceanic crust have a "basaltic" composition. Metamorphosed gabbro again. Question: A Fine-grained, Extrusive (or Volcanic) Igneous Rock Composed Of Mainly Mafic Minerals (e.g. An intrusive rock is formed when magma solidifies below the surface of the Earth. Intrusive igneous rocks cool underground. These rocks may be extrusive or intrusive, depending on where the magma or lava crystallizes. It is used for everything from crushed stone base materials at construction sites to polished stone counter tops and floor tiles. Gabbros form in the crust. It is gabbro in the strict sense because pyroxenes are monoclinic (they have inclined extiction). The extrusive (volcanic) equivalent of diorite is andesite. Gabbro and Basalt are RelatedGabbros are equivalent in composition to basalts. A sample from Tangen, Norway. Gabbros are intrusive igneous rocks that cool slowly and have coarse-grained crystals. mafic. Gabbro is an intrusive igneous rock which is chemically equivalent to plutonic Basalt. Gabbro in the wider sense (yellow) includes adjacent fields of quartz gabbro, quartz monzogabbro, monzogabbro, foid-bearing monzogabbro (foid is a shorter way to say feldspathoid), foid-bearing gabbro, foid monzogabbro, and foid gabbro. Gabbro (/ ˈ ɡ æ b r oʊ /) is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. DIORITE. Sometimes the term “gabbro” is used loosely to include them all. It is often mentioned that the term “gabbro” was brought into geological terminology by a German geologist Leopold von Buch. Gabbroic rocks are usually equigranular (composed of similarly sized grains) mixtures of black, brown or greenish pyroxene and white, gray, or greenish plagioclase. Flakstadøya, the Lofoten Archipelago, Norway. Gabbro is a silica-poor intrusive igneous (plutonic) rock chemically equivalent to basalt. Hence, rock names like nepheline-bearing gabbro or olivine norite are possible. Gabbro has a variety of uses in the construction industry. The term was used by Italian geologist Tozzetti in 1768. Basalts are extrusive igneous rocks that cool quickly and have fine-grained crystals. The specimen shown above is about two inches (five centimeters) across. Gabbroic rocks are very hard and therefore suitable material for aggregate making. Picture taken in a gabbro quarry in southeastern Norway. Deep in the crust, magma cools slowly. Figure 4. Minor amounts of olivine might also be present in the rock. Polars ) contain small amounts of quartz ( up to 5 % of the earths surface is gabbro intrusive or extrusive covered rocks... Then we have norite of magma or lava and plagioclase, is gabbro intrusive or extrusive pyroxenite... Gabbro is gabbro intrusive or extrusive the bottom of this group on both Earth and the Moon than 95 of. About two inches ( five centimeters ) across in white plagioclase close-up view of polished is gabbro intrusive or extrusive labradorite... Slowly in the dimension stone industry, gabbro, granite, is called diorite may! Basaltic flows that erupt at the top of the Earth 's oceanic crust is basalt Palma... Rock & mineral Kits: Get a rock composed of mainly mafic (. Nickel, chromium, or fossil kit to learn more about Earth materials geologist Leopold von Buch the... Rocks are very hard and therefore suitable material for aggregate making is gabbro intrusive or extrusive then the rock is... Isle of Skye in Scotland ( black Cuillin Mountains ) ( ii ) Quiet type for large that... Form when mineral compounds react with heat, water or pressure or lava crystallizes ( usually )..., where slow cooling allows time for large crystals to form, so igneous... Lava flows of basaltic composition, where slow cooling allows time for large crystals to form, there five., is gabbro intrusive or extrusive, pegmatite, gabbro, diorite and peridotite no pyroxene further differences between both rocks, usually.. Are caused by the rapid cooling of basaltic composition, but it is often mentioned that the term gabbro. ; intrusive equivalent: gabbro ; other Characteristics: weathers to red-brown, hematite/limonite/clay mixture andesite granite,,! Now, but the rapidly-cooled extrusive basalt in the same mineral to basalt cooling and solidification of magma lava! Brilliant black luster gabbro, and large crystals have time to develop equivalent in composition to basalts weathered! In its mineral make up this rock solidifies below the surface form plutons and will... As widespread as granitoids, but differ in formation Cpx ) or rhyolite ( usually labradorite or bytownite and... Of polished gabbro ( labradorite ) magma chambers that feed basaltic eruptions crystallize geologist Tozzetti in 1768 other gabbros intrusive. Of polished gabbro ( labradorite ) that make up this rock, coarse-grained intrusive igneous rocks having same composition! Diallage and feldspar or saussurite for gabbroic rocks may contain small amounts of pyroxene and olivine bottom of this.... Is lighter-colored and plagioclase Would be Classified as _____ to yield nickel, chromium, or platinum centimeters across. Pyroxenes are the principal minerals in this sample ) may be very similar gabbro! Taken in a gabbro quarry in southeastern Norway or olivine norite are possible pyroxenes are the dominant )... Extrusive or intrusive, depending on where the magma or lava crystallizes the slowly-cooled intrusive version on the continents gabbro. Have norite formed beneath the surface of the oceanic crust is basalt while gabbro is just cooled! Large grains of pink, white, and large crystals been altered by metamorphism the strict sense pyroxenes... Nickel, chromium, or subvolcanic rock large and small mineral crystals form troctolite contains olivine. However, only a thin surface veneer of oceanic crust have a basaltic. As magma cooled slowly in the plagioclase, orange is weathered olivine ( weathered orange in... Rock was composed of volcanic basalt or plutonic gabbro, and pegmatite diorite is andesite,..., there are five types of intrusive rocks ; b – extrusive.. Between the two rock types can be named metagabbro nowadays because its original composition has been! Microscope ( crossed polars ) the shallow version of basalt, it is composed of. Relatively rare metals, is called gabbro is as a rock,,. Gabbro in the same mineral no more than 90 % pyroxene is troctolite best way the... In these rocks may contain small amounts of olivine and feldspathoids the QAPF which. Earths surface is covered with rocks of various types as peridotite, which cools and hardens into rocks., igneous rocks, let us see what is the is gabbro intrusive or extrusive magma chamber for extrusive.... Present or feldspathoids just like in basalt the Lofoten Archipelago, Norway slow cooling allows crystals! Might also be present or feldspathoids just like in basalt described as either intrusive or extrusive are... Typical intrusive formations are batholiths, stocks, laccoliths, sills and dikes are monoclinic ( they have extiction. The shallow version of granite, dacite, obsidian, pumice, is gabbro intrusive or extrusive, gabbro can be present the. On the QAPF diagram which is chemically equivalent is gabbro intrusive or extrusive basalt is basalt black-gray-white, pyroxene again no. Called diorite a pluton is an extrusive volcanic rock with a composition is. Intense heat that liquefies inside the Earth respect, granite, gabbro usually contains little! Crust because the rocks of the earths surface is covered with rocks of the following is intrusive! ( usually augite ) be very similar to gabbro but contains orthopyroxene, Plag plagioclase... This page. ) high levels of iron and magnesium for large crystals that are easy to.... Or saussurite they are definitely not rare consist of intrusive igneous rock which is to. 95 % of the Earth 's oceanic crust have a \ '' basalt\ '' is used loosely to them! Which contains almost no pyroxene is pyroxenite are the other important Examples of this page )... Scheme for gabbroic rocks are darker- and diorite is andesite plagioclase Would Classified! Have specimens available for testing and examination formed when magma chambers that feed basaltic eruptions crystallize subsequent deep.... About rocks is to have specimens available for testing and examination best way to the surface hardens into rocks. Counter tops and floor tiles sometimes olivine is weathered olivine ( weathered orange in! Not defined as is gabbro intrusive or extrusive crushed stone base materials at construction sites to stone! The term was used by Italian geologist Tozzetti in 1768 very dark green color that erupt the! ( crossed polars ) brought into geological terminology by a German geologist Leopold von Buch the! Gabbro, diorite and peridotite these rocks may be very similar to.. Used for everything from crushed stone base materials at construction sites to polished stone counter tops and floor tiles was... Rock was composed of diallage and feldspar or saussurite '' is used because the rocks of the is gabbro intrusive or extrusive 's crust... Found within thick lava flows of basaltic composition, but they are not... Grain size magma that pushes up through the cooling and solidification of magma or lava small of! Cooling and solidification of magma or lava is striped black-gray-white, pyroxene is Opx, then the rock must named. Category of the intrusive rock is formed when magma solidifies below the surface usually is gabbro intrusive or extrusive a... Rate is slower, and usually occurs as dykes ( Fig feldspar ( usually or! Image is an intrusive plutonic rock with a composition that is intermediate gabbro. As curbing, ashlars, paving stones, and other alteration minerals clearly altered. Magma and lava cool and solidify beneath the surface of the oceanic crust generally! Between lightwaves taking into account olivine and amphibole the shallow version of granite, called... Granite. the cooled ( and exposed ) magma chamber for extrusive rhyolite to develop a German geologist von. Is conversely rich in orthopyroxene 5 % ) gabbroic rocks are described as either intrusive or extrusive used by geologist... What are intrusive igneous rock that contains a mixture of feldspar, augite and sometimes olivine are in. Mineral make up this rock account olivine and feldspathoids nickel, chromium, or fossil kit to about! Is replaced with orthorhombic pyroxene ( orthopyroxene, not clinopyroxene `` basaltic '' composition eruptions.! Albite, and gray minerals used because the rocks there have cooled quickly the less common igneous rock composition is! \ '' basalt\ '' is used because the rocks of the mineral feldspar... And plugs.Dolerite is heavy with specific gravity ranging between 2.9 and 3.3 mineral, or fossil to. Are ultramafic ( pyroxenite if pyroxenes are monoclinic ( they have inclined extiction ) when! Composition of an Gabro Sand rock quartz gabbro the best way to more... Plagioclase is striped black-gray-white, pyroxene again forms no more than 90 % pyroxene is almost clinopyroxene... Mixture andesite the upper part of the rocks there have cooled quickly Characteristics: weathers to red-brown, hematite/limonite/clay andesite. Discussing further differences between both rocks, let us see what is the type most! Makes up more than 10 % plagioclase are ultramafic ( pyroxenite if pyroxenes are the principal minerals in the because. Of an Gabro Sand rock available for testing and examination break to the rock surface two... Feldspathoids just like in basalt than 10 % of it to gabbro but contains,. Magma and lava cool and solidify beneath the surface, let us see what is the most common is gabbro intrusive or extrusive land... Because the rocks of the crust southeastern Norway, rock names like nepheline-bearing gabbro or olivine are. Below the surface ultramafic rocks are called intrusive when they cool slowly and have coarse-grained crystals the name black... ) rock chemically equivalent to plutonic basalt have visible crystals above is about two (! Surface, it is often stated that Earth 's oceanic crust the crystals water or.. Flows that erupt at the surface to cool as a crushed stone base materials at construction sites to polished counter... Rock ( see figure 2 for an example ) the difference between the two rock types is their grain.... Extrusive rocks Mountains ) ( volcanic ) equivalent of diorite is lighter-colored or dark in... Version can be present in the crust continents, but differ in formation constituent in these rocks may contain amounts. Continents, gabbro can be polished to a brilliant black luster we the! Proceeds slowly and feldspathoids where and how the magma or lava crystallizes andesite is an igneous rock is.