Korzo (granite) EarthCache

HRVATSKI

Korzo ukratko

Korzo se već od ranog XIX. stoljeća počeo formirati u obliku u kakvu ga danas poznajemo, kao glavno šetalište i sastajalište Riječana, te poligon za gradnju reprezentativnih palača u obličjima stilova koji su se smjenjivali: klasicizma, historicizma, secesije, moderne... Urbanistička regulacija koja se odvijala oko polovice XIX. stoljeća predstavljala je tek uvod u još žešći tempo nasipavanja mora i reprezentativne javne izgradnje, koja će ubrzo uslijediti na nasutom terenu. No, već je tada u zaborav pala stoljetna slika primorskoga grada stiješnjenog zidinama. Danas je teško povjerovati da se sve do prekrivanja opkopnoga jarka i rušenja gradskih zidina, u drugoj polovici XVIII. stoljeća, na ovom mjestu nalazila tek šljunčana morska obala s nekoliko drvenih gatova i skladišta, brodogradilištem i gradskom ložom, pokraj koje se trgovalo žitaricama, ribom i solju.

Granitne ploče na Korzo su postavljene 1991. i 1992. godine.

O granitu

Granit je najčešći i jako raširen tip kiselih intruzivnih magmatskih stijena s najmanje 20% kvarca i do 65% alkalnog feldspata po volumenu. Obično su srednje do krupno kristalasti, a mogu biti ružičasti do tamnosivi, što ovisi o njihovom kemijskom i mineralnom sastavu.

Riječ "granit" dolazi od latinskog granum, (zrno), što se odnosi na krupnozrnatu strukturu takve holokristalne stijene.

Pojam "granitan" znači sličan granitu i primjenjuje se na granit i skupinu intuzivnih magmatskih stijena sa sličnim teksturama i neznatnim varijacijama sastava i podrijetla.

Ove stijene uglavnom se sastoje od feldspata, kvarca, tinjca i minerala amfibola, koji su međusobno povezani, nešto poput matrice jednake granulacije feldspata i kvarca s mjestimice tamnijim tinjcem biotita i amfibola (često hornblenda) pepeljasto svjetlije boje minerala.

Povremeno su pojedinačni kristali (fenokristali) veći od zemljine mase, te u tom slučaju teksturu prepoznajemo kao porfiričnu. Granitna stijena s takvom teksturom poznata je kao granit porfir.

Granitoid je općenito pojam za „lakše“ boje, krupnozrnatih magmatskih stijena. Za identifikaciju određene vrste grantoidnosti potreban je Petrografski ispit.

Granit se razlikuje od granodiorita u kojem je najmanje 35% feldspata u granitu  alkalijskog podrijetla nasuprot plagioklaza; to je kalijev feldspat koji granitu daje osobitu ružičastu boju. Riolit je vrsta granita koji pripada efuzivnim magmatskim stijenama.

Granit je gotovo uvijek masivan (nema nikakve unutarnje strukture), tvrd i težak, i zato je stekao široku primjenu kroz cijelu ljudsku povijest. U novije vrijeme široko je zastupljen i kao građevinski kamen. Prosječna gustoća granita je između 2,65 i 2,75 g/cm3, njegova tlačna čvrstoća obično je iznad iznad 200 MPa (megapaskala), a njegova viskoznost po STP-u je 3-6x10¹⁹ Pa·s (paskal sekunde).

Temperatura taljenja suhog granita, na prirodnom tlaku je oko 1215-1260°C. U prisustvu vode temperatura je smanjena na 650°C pri tlaku od nekoliko kBar (kilobar).

Granit ima slabu primarnu propusnost, ali jaku srednju propusnost.

Stijena poznata kao "crni granit" obično se naziva gabro.

Mineralogija

Granit je klasificiran prema QAPF dijagramu za grubo zrnate plutonske stijene i nazvan je prema postotku kvarca, alkalnog (lužnatog) feldspata (ortoklas, sanidin ili mikroklin) i plagioklasnog feldspata na A-Q-P polovici dijagrama. Pravi granit prema suvremenoj petrološkoj konvenciji sadrži i plagioklasne i alkalijske feldspate.

Kada je granitoid bez ili gotovo bez plagioklasa, stijena se naziva alkalno feldspatni granit.

Kada granitoid sadrži manje od 10% ortoklasa, naziva se tonalit; piroksen i amfibol su uobičajeni u tonalitu.

Granit koji sadrži i muskovit i tinjac biotit zove binarni ili dvo(a)-tinjac granit. Takvi graniti obično imaju visoki udio kalija i nizak udio plagioklasa, i obično su S-tipa granita ili A-tipa granita.

Kemijski sastav

Svjetski prosjek kemijskog sastava granita, po težinskom postotku, na temelju kemijske analize 2485:

SiO₂ 72.04%, Al₂O₃14.42%, K₂O 4.12%, Na₂O 3.69%, CaO 1.82%, FeO 1.68%, Fe₂O₃ 1.22%, MgO 0.71%, TiO₂   0.30%, P2O5 0.12%, MnO 0.05%

Pojava

Izdanci granite koji se pojavljuju na površini najčešće se formiraju kao humci i zaobljeni masivi. Ponekad se pojavljuju u kružnim depresijama okruženi nizom brežuljaka, stvarajući metamorfnu oreolu ili su oblika rogovlja (hornfels).

Granit se obično nalazi u kontinentalnim pločama Zemljine kore. Za sada je poznato da granit postoji samo na Zemlji, gdje tvori najveći dio kontinentalnih kora.

Granit se često javlja kao relativno mala, (manja od 100 km²) površinska masa (dionica), i u obliku batolita često povezanih u orogenske planinske lance.

Mali nasipi granitnih kompozicija nazivaju se apliti i često se javljaju na granicama granitnih intruzija.

Na nekim lokacijama, izrazito krupnozrnati pegmatitei spajaju se s granitom.

Granit se razvijao u zemljinoj kori tijekom svih geoloških razdoblja, iako najviše u pretkambriju.

Postanak

Granit ima felsični (feldspat i silicij) sastav koji je češći u novijem geološkom vremenu, za razliku od Zemljine ultramafitne drevne eruptivne povijesti.

Felsične stijene su manje gustoće od mafitnih i ultramafitnih stijena, i na taj način nastoje izbjeći subdukciju, dok bazaltne ili gabro stijene imaju tendenciju potonuća u plašt ispod granitnih stijena kontinentalnih kratona.  Granitne stijene čine “podrum” svih kopnenih kontinenata.

Prirodna radijacija

Granit je prirodni izvor zračenja, kao i većina prirodnog kamena.  Međutim, kod nekih vrsta granita zabilježena je veća radioaktivnost, čime je podignuta zabrinutost za ljudsku sigurnost. Kalij-40 je radioaktivni izotop slabe emisije, a sastavni je dio alkalnih feldspata, i čest sastojak granitnih stijena.  

Geigerov brojač prijavljuje i niske emisije zračenja granita koje na otvorenom prostoru nisu opasne po ljudsko zdravlje.

Da biste prijavili pronalazak potrebno je odgovoriti na sljedeća pitanja:

Možete sjesti na obližnju fontanu i uživati dok tražite odgovore!

1. Opišite teksturu i boju granita na ovoj lokaciji?
2. Granit je metamorfna stijena, što znači da unutar nje ima više različitih vrsta stijena. Koristeći sliku dolje, navedite koji su najzastupljeniji minerali u granitnim pločama na Korzu?
3. Koji element daje granitu posebnu ružičastu boju?
4. Kolika je prosječna gustoća granita?
5. Priložite fotografiju (opcionalno)

Pošaljite odgovore e-poštom (putem GC profila). Slobodno upišite pronalazak, a ako nešto nije u redu, obavijestit ću vas!

ENGLISH

Korzo

As early as at the beginning of the 20th century Korzo started to assume its modern-day outlines. The main promenade and the meeting point for Rijeka's citizens, as well as the area for erecting the symbolic palaces representing various styles including the Classical, Historical, Secessional, Modernist… The urban regulation, taking place in the mid-19th century, was only a prelude to a growing pace of reclamation and major public constructions which would soon ensue on the made up ground. However, already at that point the centuries old image of a littoral town straitened by its walls started to fade away. Today, it is hard to believe that until the moat was filled and the city walls pulled down, in the second half of the 18th century, this was only gravel seashore with a few wooden quays and storehouses, a shipyard and the city lodge next to which cereals, fish and salt were traded.

Granite slabs were set at Korzo in 1991. and 1992.

About granite

Granite is a common type of felsic intrusive igneous rock that is granular and phaneritic in texture. Granites can be predominantly white, pink, or gray in color, depending on their mineralogy. The word "granite" comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a holocrystalline rock. By definition, granite is an igneous rock with at least 20% quartz and up to 65% alkali feldspar by volume.

The term "granitic" means granite-like and is applied to granite and a group of intrusive igneous rocks with similar textures and slight variations on composition and origin. These rocks mainly consist of feldspar, quartz, mica, and amphibole minerals, which form interlocking, somewhat equigranular matrix of feldspar and quartz with scattered darker biotite mica and amphibole (often hornblende) peppering the lighter color minerals.

Occasionally some individual crystals (phenocrysts) are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic texture is known a granite porphyry.

Granitoid is a general, descriptive field term for lighter-colored, coarse-grained igneous rocks. Petrographic examination is required for identification of specific types of granitoids.

Granite differs from granodiorite in that at least 35% of the feldspar in granite is alkali feldspar as opposed to plagioclase; it is the potassium feldspar that gives many granites a distinctive pink color. The extrusive igneous rock equivalent of granite is rhyolite.

Granite is nearly always massive (lacking any internal structures), hard and tough, and therefore it has gained widespread use throughout human history, and more recently as a construction stone. The average density of granite is between 2.65[and 2.75 g/cm³, its compressive strength usually lies above 200 MPa, and its viscosity near STP is 3-6x10¹⁹ Pa·s.

Melting temperature of dry granite at ambient pressure is or 1215–1260 °C (2219–2300 °F); it is strongly reduced in the presence of water, down to 650°C at a few kBar pressure.

Granite has poor primary permeability, but strong secondary permeability.

The rock known as "black granite" is usually gabbro.

Mineralogy

Granite is classified according to the QAPF diagram for coarse grained plutonic rocks and is named according to the percentage of quartz, alkali feldspar (orthoclase, sanidine, or microcline) and plagioclase feldspar on the A-Q-P half of the diagram.

True granite according to modern petrologic convention contains both plagioclase and alkali feldspars.

When a granitoid is devoid or nearly devoid of plagioclase, the rock is referred to as alkali feldspar granite.

When a granitoid contains less than 10% orthoclase, it is called tonalite; pyroxene and amphibole are common in tonalite.

A granite containing both muscovite and biotite micas is called a binary or two-mica granite. Two-mica granites are typically high in potassium and low in plagioclase, and are usually S-type granites or A-type granites.

Chemical composition

A worldwide average of the chemical composition of granite, by weight percent, based on 2485 analyses:

SiO₂ 72.04%, Al₂O₃ 14.42%, K₂O 4.12%, Na₂O 3.69%, CaO 1.82%, FeO 1.68%, Fe₂O₃ 1.22%, MgO 0.71%, TiO₂  0.30%, P₂O₅ 0.12%, MnO 0.05%

Occurrence

Outcrops of granite tend to form tors and rounded massifs. . Granites sometimes occur in circular depressions surrounded by a range of hills, formed by the metamorphic aureole or hornfels.  Granite is usually found in the continental plates of the Earth's crust.

Granite is currently known to exist only on Earth, where it forms a major part of the continental crust. Granite often occurs as relatively small, less than 100 km² stock masses (stocks) and in batholiths that are often associated with orogenic mountain ranges. Small dikes of granitic composition called aplites are often associated with the margins of granitic intrusions. In some locations, very coarse-grained pegmatite masses occur with granite. Granite has been intruded into the crust of the Earth during all geologic periods, although much of it is of Precambrian age. Granitic rock is widely distributed throughout the continental crust and is the most abundant basement rock that underlies the relatively thin sedimentary veneer of the continents.

Origin

Granite has a felsic composition and is more common in recent geologic time in contrast to Earth's ultramafic ancient igneous history. Felsic rocks are less dense than mafic and ultramafic rocks, and thus they tend to escape subduction, whereas basaltic or gabbroic rocks tend to sink into the mantle beneath the granitic rocks of the continental cratons. Therefore, granitic rocks form the basement of all land continents.

Natural radiation

Granite is a natural source of radiation, like most natural stones. However, some granites have been reported to have higher radioactivity, thereby raising some concerns about their safety.

Potassium-40 is a radioactive isotope of weak emission, and a constituent of alkali feldspar, which in turn is a common component of granitic rocks, more abundant in alkali feldspar granite and syenites. Naturally, a Geiger counter should register this low effect.

To get the log permission, please answer the following questions:

You can sit on a nearby fountain and enjoy while you are searching for answers!

1. Describe the texture AND color of the granite at this location?
2. Because granite is a metamorphic rock, it has many different types of rocks inside of it. Using the picture above, what is the most abundant mineral in this piece of granite?
3. Which mineral gives many granites a distinctive pink color?
4. How much is average density of granite?
5. Take a photo  with GPS (optional).

Please email me your answers in english (via GC-Profile). You don't have to wait for a permission to log. If your answers are incorrect, I will inform you.