Two Granites EarthCache

At the listed coordinates you will find nice fountain that is built of two types of granite, and granite is type of igneous rock.

Igneous Rocks

Igneous rocks are formed by cooling of hot magma or lava and by its solidification. Although both magma and lava are essentially molten rock, the magma is molten rock while it is still below the surface and lava is molten rock on the surface of planet usually expelled by a volcano during an eruption. If the rock is formed from magma it is also called plutonic and if it is formed from lava it is called volcanic. The term “plutonic” came from the name of classical god of the underworld - Pluto, and the term “volcanic” came from the fact that the rock is formed from lava erupted from a volcano.

Igneous Rocks

Plutonic rocks are also called intrusive rocks. That means that magma is slowly pushed up from the mantle within the earth and it intrudes by force into any cracks or spaces it can find. On the other hand, volcanic rocks are also called extrusive rocks because they are formed when hot magma extrudes onto the surface of planet as lava. The process of cooling of hot magma deep below surface of planet lasts much longer than cooling of hot lava on the surface of planet. Since it lasts longer, the larger crystals can grow during the process of solidification of intrusive rocks when compared to extrusive rocks.

Crystal Size

During the process of cooling and solidification of magma or lava, the process of crystallization or formation of crystals might or might not happen. So, that means that there are igneous rocks with crystals and igneous rocks without crystals. Those igneous rocks that are formed with crystals can be divided into those that have crystals large enough to be seen by the naked eye (they are also called phaneritic rocks), and those that have crystals too small to be seen by the naked eye (they are also called aphanitic rocks). Phaneritic rocks are also intrusive rocks, because they have more time to develop larger crystals during cooling of magma deep below surface of planet. Aphanitic rocks are also extrusive rocks because lava cools on surface of the planet and it happens much faster than below surface.

Phaneritic vs. Aphanitic Rocks

Crystals in igneous rocks are seen in the form of grains of different colors and different sizes. Regarding their size, grains can be: (1) fine-grained (diameter of the grains is smaller than 1 millimeter), (2) medium-grained (diameter of the grains is between 1 and 5 millimeters), and (3) coarse-grained (diameter of the grains is larger than 5 millimeters). Intrusive or plutonic rocks usually have larger crystals because the process of cooling and solidification lasts much longer below the surface of planet. So, they are usually coarse-grained. Extrusive or volcanic rocks usually have smaller crystals because the process of cooling and solidification lasts much shorter on the surface of planet. So, they are usually fine-grained.

Mineral Composition

Granite is igneous rock that contains three main minerals: quartz, potassium feldspar and plagioclase feldspar. These three minerals make up more than 80% of granite. Other minerals that can be found in granite are: mica (muscovite, biotite, lepidolite) and hornblende (amphibole). These additional minerals are called accessory minerals. The chemical composition of granite is typically 70-77% silica, 11-13% alumina, 3-5% potassium oxide, 3-5% sodium oxide, 1% lime, 2-3% total iron, and less than 1% magnesia and titania.

Mineral Composition of Igneous Rocks

Mineral composition of granite determines its color. Most types of granite are red, pink, gray or white with dark mineral grains visible throughout the rock.

Each mineral within granite has its own unique color. Quartz may appear gray, but is actually colorless and is reflecting and fusing the colors of the white and black minerals surrounding it. Plagioclase feldspar is white with a porcelaneous luster. Potassium feldspar is generally the one that give granite its color variations from yellow to orange to pink or blue. Dark potassium feldspar can give granite its black varieties. Mica usually has silver color (muscovite), black or brown color (biotite) or violet or pink color (lepidolite) and provide the sparkle that some granites possess. The hornblende and biotite provide granite with the black grains portion of the usual granite look.

The overall color of granite emerges from those unique colors of minerals that are contained in granite. Grey color of granite occurs when feldspar, usually white mineral, contains admixtures of dark-colored minerals of mica or pyroxenes. Red color of granite occurs when feldspar contains impurities of hematite. Even small amounts of hematite in feldspar – only 0.7-1.0% can cause red color in granite. Pink color occurs when the amount of hematite in feldspar does not exceed 0.3-0.4%. Green color of granite occurs when it contains green variety of potassium feldspar which is known as amazonite and it is a semiprecious stone.

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Sources

Na izlistanim koordinatama pronaći ćete lijepu fontanu koja je izrađena od dvije vrste granita, a granit je vrsta magmatske stijene.

Magmatske stijene

Magmatske stijene nastaju hlađenjem magme ili lave i njihovim skrutnjavanjem. Iako su i magma i lava zapravo rastaljene stijene, magma je rastaljena stijena koja se još nalazi ispod površine planeta, dok lava predstavlja rastaljenu stijenu koja se nalazi na površini planeta i koja je najčešće izbačena iz unutrašnjosti planeta erupcijom vulkana. Ako je stijena nastala od magme tada se naziva plutonska stijena, a ako je nastala od lave tada se naziva vulkanska stijena. Termin “plutonski” je došao od imena rimskog boga podzemlja – Plutona. Termin “vulkanski” se koristi zbog činjenice da je ta vrsta stijena nastala od lave koja je izbačena vulkanskom erupcijom.

Magmatske stijene

Plutonske stijene se još nazivaju i intruzivne stijene. To znači da magma polagano pritišće prema gore iz zemljinog plašta i prodire silom u sve pukotine i slobodan prostor koji joj se nađe na putu. S druge strane, vulkanske stijene se još nazivaju i ekstruzivne stijene zato što nastaju kada magma izbije na površinu planeta u vidu lave. Proces hlađenja magme duboko ispod površine planeta traje puno duže od hlađenja lave na površini planeta. S obzirom da proces traje duže, veći kristali se formiraju tijekom skrutnjavanja intruzivnih stijena u odnosu na ekstruzivne stijene.

Veličina kristala

Tijekom procesa hlađenja i skrutnjavanja magme ili lave može, ali i ne mora doći do procesa kristalizacije, tj. do formiranja kristala može, ali i ne mora doći. To znači da postoje magmatske stijene s kristalima i magmatske stijene bez kristala. Magmatske stijene koje su formirane s kristalima mogu se podijeliti na stijene koje imaju kristale koji su dovoljno veliki da ih se može vidjeti golim okom i one se nazivaju faneritične stijene, te na stijene kod kojih se kristali ne mogu vidjeti golim okom i one se nazivaju afanitične stijene. Faneritične stijene su ujedno i intruzivne stijene jer su imale dovoljno vremena za razvoj velikih kristala tijekom hlađenja magme duboko ispod površine planeta. Afanitične stijene su ujedno i ekstruzivne stijene jer se lava hladi na površini planeta i taj proces se događa puno brže nego ispod površine planeta.

Faneritične vs. afanitične stijene

Kristali u magmatskim stijenama su vidljivi u obliku zrna različitih boja i veličina. S obzirom na njihovu veličinu, zrna mogu biti: (1) fino-zrnata (promjer zrna je manji od 1 mm), (2) srednje-zrnata (promjer zrna je između 1 i 5 mm), i (3) krupno-zrnata (promjer zrna je veći od 5 mm). Intruzivne ili plutonske stijene uobičajeno imaju veće kristale zato što process njihovog hlađenja i skrutnjavanja traje duže. Stoga su ove stijene najčešće krupno-zrnate. Ekstruzivne ili vulkanske stijene uobičajeno imaju manje kristale zato što process njihovog hlađenja i skrutnjavanja traje puno kraće. Stoga su ove stijene najčešće fino-zrnate.

Mineralni sastav

Granit je magmatska stijena koja sadrži tri glavna minerala: kvarc, kalijev feldspat i plagioklasni feldspat. Ova tri minerala čine više od 80% granita. Drugi minerali koji se mogu naći u granitu su: tinjac (muskovit, biotit, lepidolit) i hornblend (amfibol). Kemijski sastav granita je tipično 70-77% silicijev dioksid, 11-13% aluminijev oksid, 3-5% kalijev oksid, 3-5% natrijev oksid, 1% vapno, 2-3% ukupno željezo i manje od 1% magnezijev oksid i titanijev dioksid.

Mineralni sastav magmatskih stijena

Mineralni sastav granita određuje njegovu boju. Većina vrsta granita su crvene, roza, sive ili bijele boje s tamnim zrncima minerala vidljivim kroz cijelu stijenu.

Svaki mineral koji čini granit ima svoju vlastitu boju. Kvarc se može činiti sivim, ali je zapravo bezbojan i zapravo reflektira i spaja boje bijelih i crnih minerala koji ga okružuju. Plagioklasni feldspat je bijele boje s porculanskim sjajem. Kalijev feldspat daje granitu varijacije boja od žute do narančaste do roza do plave. Tamni kalijev feldspat može dati crne varijante granita. Tinjac je najčešće srebrne boje (muskovit), crne ili smeđe boje (biotit) ili ljubičaste ili roza boje (lepidolit). Hornblend i biotit su vidljivi kao crna zrna u granitu i daju mu njegov specifičan izgled.

Cjelokupna boja granita nastaje od navedenih boja pojedinačnih minerala koji se nalaze u granitu. Siva boja granita nastaje kada feldspat, koji je inače bijeli mineral, sadrži dodatke minerala tamnih boja - tinjca i piroksena. Crvena boja granita nastaje kada feldspat sadrži hematit. Čak i male količine hematita u feldspatu - svega 0,7-1,0% - mogu uzrokovati crvenu boju granita. Roza boja nastaje kada udio hematita u feldspatu ne prelazi 0,3-0,4%. Zelena boja granita nastaje kada granit sadrži zelenu varijantu kalijevog feldspata koja j epoznata kao amazonit i smatra se poludragim kamenom.

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