Crkva sv. Kvirina
Crkva sv. Kvirina, posvećena zaštitniku grada Krka, lijep je primjer romaničke sakralne arhitekture u gradu Krku. Danas je dio cjeline katedralnog kompleksa. Prvi podatak o sv. Kvirinu datira iz 1335. kada su Krčani dali najamninu otoka Plavnika „za popravak crkve sv. Kvirina u Krku“. Pretpostavlja se da je izgrađena u 12. stoljeću. Posebnost je crkve sv. Kvirina u njezinoj dvoetažnosti i zemljopisnoj orijentaciji, budući da je njezina apsida vrlo netipično usmjerena prema jugu, vjerojatno zbog skučenog prostora na kojemu je izgrađena. Donja crkva ima titular sv. Margarite, mučenice iz Antiohije, dok je gornja posvećena sv. Kvirinu, zaštitniku grada Krka. Gornja i donja crkva u svojoj se unutrašnjosti bitno razlikuju, s obzirom da donja ima dva broda, od kojega je istočni širi od zapadnoga, a gornja tri broda. Tu razliku diktira troapsidalan južni završetak na gornjem katu i dvoapsidalan u prizemlju. Na mjestu prizemne istočne apside zid je skraćen i napravljen je prolaz iz kojega se ulazi u katedralu i crkvu sv. Margarite. Ova je romanička crkva izgrađena od bijeloga domaćeg kamena. Estetici crkve naročito doprinosi troapsidalan poluvaljkasti završetak, nejednako završen s istočne i zapadne strane, koji osim dubokih malih prozorskih otvora, kao jedinu istaknutiju dekoraciju, ima slijepe romaničke arkadice na vrhu te borduru od brušenoga crvenkastog domaćeg kamena (mandorlat) u sredini.
Sv. Kvirin i katedrala u početku nisu bili spojeni objekti. Poznato je da je biskup Lambert 1290. dobio papinu dozvolu za sakupljanje milostinje kako bi izveo neke vrlo skupe radove na katedrali nakon čega je, pretpostavljamo, katedrala spojena sa Sv. Kvirinom. Crkve su bile povezane tako što je gornja crkva imala veliki otvor, gotovo za širinu srednjega katedralnog broda. Ovim spajanjem, gornja crkva postala je matroneum katedrale iz kojega su žene sudjelovale na misi koja se odvijala u katedrali. Nakon što su u katedrali postavljene orgulje, otvor između objekata u potpunosti je zatvoren i ostala su samo vrata. Isto postoji mogućnost da je sv. Kvirin imao funkciju palatinske kapele krčkog biskupa ili pak zapadnog zdanja (galerija, westwerk), odakle su krčki knezovi pratili misu.
Još u starim krčkim statutima postoji naredba notarima da moraju kod pisanja oporuka spomenuti oporučitelju ako želi nešto ostaviti za crkvu sv. Kvirina, krčkog zaštitnika. U donjoj se crkvi i danas misi, dok je gornja crkva (sv. Kvirin) prenamijenjena u muzejski prostor.
Katedrala Uznesenja Blažene Djevice Marije
Vođeni idejom kontinuiteta kultnih sakralnih građevina, prvu bi krčku katedralu trebalo tražiti na mjestu današnje katedrale. Većina crkava u gradu Krku samo su odrazi kontinuiteta crkvene gradnje koje kroz povijest mijenjaju svoj izgled pod utjecajem građevinskog trenda odgovarajuće povijesne epohe.
Kada danas promatramo krčku katedralu sv. Marije vidimo gotov produkt srednjeg vijeka, koji od njezine velike rekonstrukcije u romaničkom periodu do današnjih dana, usprkos malim nadogradnjama gotičke i renesansne faze, zadržava svoj izgled.
Prve istraživačke radove na kompleksu katedrale pokrenuo je pop Ivan Žic-Rokov koji nam donosi podatke o nalazu krstionice. Nedugo nakon, počela su i prva arheološka istraživanja koja je vodio Andrija Mohorovičić. Nalazi dokazuju postojanje prvotnog antičkog sloja predstavljenog kroz objekt termi. Terme su datirane u 1. stoljeće, a značajna promjena se, prema zaključcima Mohorovičića, dogodila krajem 4. st. kada je unutar zidova termi izgrađen mali oratorij s krstionicom. To je bio začetak preobrazbe koja će tijekom 5. stoljeća dovesti do potpune transformacije antičkih termi u ranokršćansku baziliku. Danas su od izvorne bazilike ostala tek dva kapitela. Možemo tek pretpostavljati da se, obzirom na njene gabarite, radilo o velebnoj crkvi. U ranom srednjem vijeku crkva je dobila oltarnu pregradu. To potvrđuju nalazi fragmenata predromaničke plastike koji su pronađeni u zidu katedrale. Dio tih spolija izložen je u crkvi sv. Kvirina.
U romanici su na cjelokupnom katedralnom kompleksu izvršene značajne preinake. Natpis u katedrali spominje rekonstrukciju kolonada (columnarum opus) u XII. stoljeću od strane neimenovanog krčkog biskupa (spomenutog inicijalom D). Ova se graditeljska djelatnost čini najvjerojatnijom u vrijeme biskupa Dabra (Dobro – Bonus) oko 1179. Južna arkadura ima devet, po formi nejednakih stupova i četiri tipa kapitela. Lukova ima deset, međutim, najistočniji je zazidan radi produženja svetišta. Sjeverna arkatura također ima devet stupova s deset lukova, od kojih je istočni zazidan. Stupovi sjeverne arkature također su različiti sa četiri tipa kapitela i s dva kapitela životinjskih motiva.
Biskup Donat a Turre (1484. – 1515.) započeo je pregradnju apside, a nastavio ju je 1538. g. krčki plemić Blaž Zuttinis, te je dovršio 1539. godine. Pobočne lađe završavaju ravnim zidovima koji sijeku uzdužne zidove pod pravim kutom, a nalaze se na mjestu starijih apsidalnih konstrukcija koje su kasnije porušene, a otvor pod lukom niše zazidan je u 16. stoljeću.
Značajne promjene u pobočnim lađama bazilike nastale su gradnjom raznih kapela priključenih uz bočne zidove crkve tijekom 15. i 16. stoljeća. Na taj način mijenjao se broj i položaj oltara. Polovicom 15. stoljeća podignuta je gotička kapela sv. Barbare, a koncem 15. stoljeća kapela sa krsnim zdencem. Kapela Srca Isusova podignuta je krajem 16. stoljeća. Južnu kapelu, u kojoj se danas nalazi raspelo, prvu do vrata, dala je sagraditi žena kneza Ivana Frankopana, polovicom 15. stoljeća. Kapele s oltarima sv. Nikole i Gospe karmelske dao je podići biskup Petar Bembo oko 1570. godine.
Katedrala je nosi titular Blažene Djevice Marije, što je još jedan od indikatora njezina vrlo ranog postojanja. Prema pronađenom natpisu o gradnji crkve povjesničari nameću mogućnost postojanja crkve još u drugoj polovici 5. i početkom 6. stoljeća, čime se titular crkve vezuje uz Efeški koncil (431.) i veliko slavlje prilikom priznanja Marije kao Majke Božje. Svakako govorimo o romaničkoj katedrali izuzetno bogatog inventara, iz starijih i nešto mlađih razdoblja, i povijesno gledano, o važnom biskupskom središtu na prostoru Sjevernog Jadrana.
Zvonik
Zvonik krčke katedrale nalazi se na sjevernom pročelju sv. Kvirina. Mjesto njegove izgradnje odredio je mletački providur Vinciguerra 1489. godine, a gradnja je dovršena 1515. godine. U zvonik je 1714. udario grom nakon čega se raspuknula i pala glavna zaglavna kamena piramida. Šezdesetih godina 18. stoljeća napravljena je temeljita restauracija prema nacrtima mletačkog arhitekta Petra Checchia. Tada je na zvonik postavljen drveni anđeo obložen bakrenim limom izrađen u Mlecima. Iako je zvonik napravljen naknadno, predstavlja prepoznatljiv dio krčkog katedralnog kompleksa i gradske vizure. Kroz svoju povijest nekoliko je puta restauriran. Od godine 1973. na vrhu zvonika nalazi plastični anđeo napravljen prema kalupu već dotrajaloga starog anđela.
Izvori:
Krčka kulturna baština
Što je vapnenac?
Vapnenac je sedimentna stijena sastavljena uglavnom od kalcijevog karbonata (CaCO3) u obliku mineralnog kalcita. Vapnenačke forme najbolje su vidljive i prepoznatljive u toplim, plitkim morskim vodama. Vapnenac je obično biološka (organska) sedimentna stijena nastala taloženjem školjaka, koralja, algi i fekalnih ostataka.
Također, može biti i kemijski (anorganski) formirana sedimentna stijena nastala taloženjem kalcijevog karbonata iz jezera, mora ili oceana.
Nastajanje vapnenca - marinski
Većina vapnenaca nastaje u plitkim, mirnim i toplim morskim vodama. U morskom okruženju lako dolazi do izvlačenja kalcijevog karbonata iz školjaka i kostura potrebnih za formiranje vapnenca. Nakon što morski organizmi izumru njihove oklopne i skeletne krhotine talože se kao sediment koji se pretvara u vapnenac. Njihovi otpadni proizvodi (kakica) također mogu doprinijeti taloženju. Vapnenci nastali na ovakav način nazivaju se biološkim sedimentnim stijenama. Njihovo biološko podrijetlo otkrivamo prisutnošću fosila u stijeni.
Neki vapnenci mogu nastati izravnim taloženjem kalcijeva karbonata iz morske ili slatke vode. Vapnence nastale na ovaj način nazivamo kemijskim sedimentnim stijenama. Po svojoj strukturi manje su obilni od biološkim vapnenaca.
Danas je na Zemlji puno vapnenačko oblikovanih okruženja. Većina ih se nalazi u pličinama između 30 stupnjeva sjeverne geografske širine i 30 stupnjeva južne geografske širine.
Nastajanje vapnenca - isparavanjem
Vapnenac može nastati i isparavanjem. Stalaktiti, stalagmiti i ostali spiljski oblici takvi su primjeri vapnenca. U pećini, kapljice vode cure odozgo kroz pukotine ili pore i dolaze do spiljskih stropova. Prije pada na pod spilje može doći do isparavanja. Kako voda isparava tako se kalcijev karbonat taloži na stropu spilje. Tijekom vremena proces isparavanja može rezultirati nastankom vrhova kalcijeva karbonata na stropu spilje. Takve naslage počinju tvoriti stalaktite. Moguć je i obrnuti proces kada se isparavanje događa na tlu spilje što omogućava nastanak stalagmita.
Vapnenac koji tako tvori spiljske oblike poznat je i kao „sedra“ te pripada kemijskim sedimentnim stijenama. Stijena poznata kao „tuf“ vapnenac je nastao isparavanjem vrućih izvora, obala jezera ili sličnih područja.
Sastav vapnenca
Vapnenac je po definiciji kamen koji sadrži najmanje 50% kalcijevog karbonata u obliku kalcitne mase. Svi vapnenci sadržavaju barem nekoliko postotaka drugih materijala. To mogu biti maleni udjeli kvarca, feldspata, gline, pirita, siderita i ostalih materijala. Također mogu sadržavati veće komade rožnjaka, pirita ili siderita.
Prisustvo kalcijevog karbonata u vapnencu daje mogućnost lake identifikacije stijene, koja se izložena hladnoj otopini 5%-tne solne kiseline – zapjeni.
Vrste vapnenca
Postoji puno naziva koji se koriste za vapnenac. Ti se nazivi temelje na tome kako je stijena nastala, njezinom izgledu, sastavu i ostalim čimbenicima. Slijedi nekoliko najčešćih naziva:
Kreda: meki vapnenac s vrlo finom teksturom obično bijele ili svijetlo sive boje. Uglavnom nastaje od vapnenačkih ostataka ljusaka mikroskopskih morskih organizama, npr. foraminifera ili vapnenačkih ostataka mnogobrojnih vrsta morskih algi.
Kokvina: Slabo-zacementiran (povezan) vapnenac koji je uglavnom nastao od krhotina slomljenih ljusaka.
Fosilizirani vapnenac: kao što mu naziv govori sadrži obilje fosila. Najčešće se radi o školjkama i kostima organizama koji tvore vapnenac.
Litografski vapnenac: gusti vapnenac s vrlo finim i vrlo ujednačenim veličinama zrna koji se pojavljuje u tankim naslagama koje se mogu lagano raslojavati u vrlo glatku površinu. Krajem 18. stoljeća razvijena je litografija. Litografija je postupak nastanaka likovnog djela u kojoj se po vapnenačkoj ploči crta masnom kredom ili litografskim tušem, pri čemu se stvara vapneni sapun. Zatim se ploča prekrije dušičnom kiselinom pomiješanom s arapskom gumom rastopljenoj u vodi. Vapneni sapun odbija zakiseljenu otopinu te su tako njenom djelovanju izloženi samo neiscrtani dijelovi kamena. Nakon toga se kamen ovlaži vodom i prijeđe valjkom premazanim tiskarskom bojom. Vlažna čista površina ne prima masnu boju, prima je jedino crtež (vapneni sapun) koji nije upio vodu. Litografija je omogućila vrlo laganu proizvodnju kopija te je postala jako raširena.
Oolitski vapnenac: sastavljen uglavnom od kalcijevog karbonata "oolites", male sfere nastale koncentričnim taloženjem kalcijevog karbonata na pješčanom zrnu ili ostatku školjke.
Sedra: vapnenac nastao isparavanjem oborina, najčešće u spiljama, nastaju spiljski oblici poput stalaktita ili stalagmita.
Tuf: vapnenac nastao taloženjem voda bogatih kalcijem iz vrućih izvora, obala jezera ili sličnih mjesta.
Fosili
Na svim spomenutim lokacijama, pronaći ćete ne samo lijep primjer sedimentne stijene vapnenca, već i veliki broj fosila. Što su uopće fosili? Oni su sve ono što dokazuje život u prošlim vremenima. Taj se dokaz prošlog života javlja u dva oblika. On može biti izravan ili neizravan.
Izravan dokaz života su fosili koje čine čvrsti dijelovi organizama. U slučaju životinja, to mogu biti fosilizirane kosti ili školjke. Ili, kada su u pitanju biljke, to može biti fosilizirano drvo ili lišće. U nekim slučajevima, fosiliziran može biti i cijeli organizam, i njegovi meki i njegovi čvrsti dijelovi. Primjeri takvih fosila su insekti zarobljeni u jantaru ili mamuti smrznuti u ledu.
Neizravan dokaz života su fosilni tragovi. To su različiti otisci stopala, repova, tragova, koje su organizmi ostavljali, a zatim su fosilizirani. Koproliti (fosilizirana kakica) su također jedan primjer fosilnih tragova.
Klasifikacija
Dva su velika klasifikacijska sustava kojima se služimo prilikom identifikacije i klasifikacije vapnenačkih i karbonatnih stijena: Folkov i Dunhamov.
Folkova klasifikacija
Robert L. Folk razvio je klasifikacijski sustav koji u prvi plan stavlja detaljnu strukturu zrna i naglašava primarnu detaljnost sastava zrna i ostalih materijala u karbonatnim stijenama. Razlikuje tri vrste sastojaka: alokeme (zrna), matriks (uglavnom mikrit) i cement (sparit). Folkov sustav koristi dvodijelne nazive: prvi dio se odnosi na dominantnost zrna, a drugi na prevladavajuće vezivo (mikrit ili sparit). Prilikom korištenja Folkovog sustava preporuča se koristiti petrografov mikroskop jer je lakše odrediti prisutne komponente u svakom uzorku.
Dunhamova klasifikacija
Dunhamova klasifikacija temelji se na strukturnim značajkama. Svako ime temelji se na teksturi zrna koje čini vapnenac. Dunham je 1962. godine objavio svoj sustav klasifikacije koji dijeli stijene u četiri glavne skupine temeljem relativnih proporcija grubljih klastičnih čestica. Dunhanovi nazivi osnova su za određivanje stijena.
Bavio se pitanjem jesu li ili nisu izvorna zrna u međusobnom kontaktu, podržavaju li se međusobno ili su karakteristična vidljiva razgraničenja. Za razliku od Folka, Dunham se bavio poroznošću stijena. Dunhamova klasifikacija je korisnija i kvalitetnija jer se temelji na teksturi, a ne na ispitivanju zrna u uzorku.
Prošećite oko Katedrale te da biste prijavili pronalazak odgovorite na sljedeća pitanja:
1. Opišite teksturu i boju vapnenca na zvoniku!
2. Je li vapnenac nastao:
a) marinski (objasnite)
b) isparavanjem (objasnite)
3. Je li vapnenac:
a) biološkog podrijetla (objasnite)
b) kemijskog podrijetla (objasnite)
4. Zašto je Dunhamova metoda klasifikacije bolja od Folkove?
5. Priložite sliku s GPS-om (nije obvezno)
Pošaljite odgovore e-poštom (putem GC profila). Slobodno upišite pronalazak, a ako nešto nije u redu, obavijestit ću vas!
Church of St Kvirin
The church of St Kvirin, dedicated to the patron saint of the City of Krk, is a beautiful example of the Romanesque sacral architecture in the city of Krk. Today it forms a part of the entire cathedral complex. The first information about St Kvirin originate from 1335, when the people of Krk gave the money from the rent for the isle of Plavnik to “repair the church of St Kvirin in Krk”. It is supposed that the church was built in the 12th century. It is different because of its two levels and its geographical orientation, as its apse is quite untypically directed towards the south, probably owing to the restricted space in which it was built. The lower part bears the name of St Margaret, the martyr saint from Antakya, while the upper level is dedicated to St Kvirin, the patron saint of the city of Krk. The interior of the upper and lower levels is quite different; the lower level has two naves, the eastern nave being wider than the western, while the upper level has three naves. This difference is determined by the three-apse southern end on the upper level and the two apses on the ground floor. In the ground floor eastern apse, the wall is reduced and a passage was made towards the cathedral and the church of St Margaret. This Romanesque church was built from the local white stone. The three-apse semi-cylindrical ends, uneven on the eastern and on the western side, especially contribute to the church’s aesthetics. Besides the deep window openings, their only pronounced decoration consists of a blind Romanesque arcade on the top and the edging made of reddish local stone (called mandorlat) in the middle.
At the beginning, St Kvirin and the Cathedral were not connected. It is known that in 1290, bishop Lambert obtained the pope’s permission to collect alms to perform some very expensive works on the Cathedral, after which, it is supposed that the Cathedral was joined to the St Kvirin. Originally, the churches were joined so that the upper church had a large opening, extending almost along the entire length of the central cathedral nave. By such joining, the upper church became the cathedral’s matroneum, where the women used to stand during mass in the Cathedral. After the church organ was placed in the Cathedral, the opening between the two edifices was entirely closed, leaving just one door. Still, there is a possibility that St Kvirin was a palatine chapel of the Krk bishop or a western structure (westwerk gallery) from where the Krk princes followed mass.
Even in the old statutes of Krk there is a regulation stating that during writing wills, the notaries had to ask the maker of the will if he wanted to leave something to the church of St Kvirin, the patron saint of Krk. Mass is still held today in the lower church, while the upper church (St Kvirin) was converted into a museum.
Cathedral of the Assumption of the Blessed Virgin Mary
Based on the idea of the continuity of sacral edifices, the first Krk cathedral should be on the place of the today’s cathedral. Most churches in the city of Krk are merely reflections of the continuity of church construction, changing its appearance through history under the influence of architectural trends in the corresponding historical epoch.
Today, when we observe the Krk cathedral of St Mary, we can see a product of the Middle Ages, which after a major reconstruction in the Romanesque period, kept its appearance until today, despite minor additional construction in the Gothic and Renaissance era.
The first research works on the cathedral complex were initiated by the priest Ivan Žic-Rokov, who wrote about finding the baptistery. Not so long afterwards, Andrija Mohorovičić started with the first archaeological research. His findings proved the existence of the original ancient layer represented by the thermae. The thermae were dated into the 1st century, while according to Mohorovičić, a significant change happened at the end of the 4th century when a small oratorium with a baptistery was built within the walls of the thermae. This was the inception of a transformation which during the 5th century brought to a complete transformation of the ancient thermae into an early Christian basilica. Today only two capitals remained of the original basilica. We may only assume that, considering its dimensions, this was a grand church. In the early Middle Ages, the church got an altar partition. This was confirmed by the discovery of fragments of pre-Romanesque plastics in the walls of the cathedral. A part of these spoliae is displayed in the church of St Kvirin.
The entire complex of the cathedral underwent significant alterations in the Romanesque period. The inscription in the cathedral mentions a reconstruction of the colonnade (columnarum opus) in the 12th century by an unnamed Krk bishop (mentioned only by the initial D). This kind of construction activity seems most probable at the time of the bishop Dabar (Dobro – Bonus) around 1179. The southern arcade has nine unequal columns and four types of capitals. There are ten arches, but the easternmost one was walled in to extend the sanctuary. The northern arcade also has nine columns with ten arches, easternmost one was walled in. The columns of the northern arcade are also different with four types of capitals and two capitals with animal motifs.
The bishop Donat a Turre (1484 – 1515) started to partition the apse, and this was continued in 1538 by the Krk nobleman Blaž Zuttinis, and finally ended in 1539. The side naves end in flat walls, which cross the longitudinal ones under a right angle. They can be found on the place of the older apse structures which were demolished, while the opening under the niche arch was walled in the 16th century.
Significant changes in the side naves of the basilica emerged after the construction of various chapels, attached to the side walls of the church during the 15th and 16th centuries. Thus, the number and the position of the altars changed. The Gothic chapel of St Barbara was erected in the middle of the 15th century, and a chapel with a baptism well at the end of the 15th century. The Chapel of the Heart of Christ was built at the end of the 16th century. The wife of the prince Ivan Frankopan had the southern chapel, the first from the door, built in the middle of the 15th century, and today it holds the Crucifix. The bishop Petar Bembo had the chapels with the altars of St Nicholas and Our Lady of Mount Carmel built around 1570.
The Cathedral is dedicated to the Blessed Virgin Mary, which also indicates its early origin. According to a discovered inscription about the construction of the church, the historians suggest the possibility that the church existed in the second half of the 5th century and the beginning of the 6th century, which connects the titular of the church with the Council of Ephesus (year 431) and the great celebration after accepting Mary as the Mother of God. This is definitely a Romanesque cathedral with an extremely rich inventory dating back into older and earlier periods, and historically speaking, this is an important diocesan centre in the area of the Northern Adriatic.
Bell Tower
The bell tower of the Krk cathedral is situated at the northern front of St Kvirin. The place of its construction was determined by the Venetian provveditore Vinciguerra in 1489, and the construction finished in 1515. In 1714, a lightning struck the tower, causing the damage and fall of the main stone pyramid. In the 1960s, there was a thorough restoration of the tower according to the designs of the Venetian architect Pietro Checchi. That is when the wooden angel coated with copper metal sheets, made in Venice, was placed on the tower. Although the tower was made subsequently, it represents a recognizable part of the Krk cathedral complex and the city view. Throughout its history, it was restored several times. Since 1973, there is a plastic angel on top of the tower, made according to the cast of the worn-out old angel.
Sources:
Krk's cultural heritage
What is Limestone?
Limestone is a sedimentary rock composed primarily of calcium carbonate (CaCO3) in the form of the mineral calcite. It most commonly forms in clear, warm, shallow marine waters. It is usually an organic sedimentary rock that forms from the accumulation of shell, coral, algal and fecal debris. It can also be a chemical sedimentary rock formed by the precipitation of calcium carbonate from lake or ocean water.
Limestone-Forming Environment - Marine
Most limestones form in shallow, calm, warm marine waters. That type of environment is where organisms capable of forming calcium carbonate shells and skeletons can easily extract the needed ingredients from ocean water. When these animals die their shell and skeletal debris accumulate as sediment that might be lithified into limestone. Their waste products can also contribute to the sediment mass. Limestones formed from this type of sediment are biological sedimentary rocks. Their biological origin is often revealed in the rock by the presence of fossils.
Some limestones can form by direct precipitation of calcium carbonate from marine or fresh water. Limestones formed this way are chemical sedimentary rocks. They are thought to be less abundant than biological limestones.
Today Earth has many limestone-forming environments. Most of them are found in shallow water areas between 30 degrees north latitude and 30 degrees south latitude.
Limestone-Forming Environment - Evaporative
Limestone can also form through evaporation. Stalactites, stalagmites and other cave formations (often called "speleothems") are examples of limestone that formed through evaporation. In a cave, droplets of water seeping down from above enter the cave through fractures or other pore spaces in the cave ceiling. There they might evaporate before falling to the cave floor. When the water evaporates, any calcium carbonate that was dissolved in the water will be deposited on the cave ceiling. Over time this evaporative process can result in an accumulation of icicle-shaped calcium carbonate on the cave ceiling. These deposits are known as stalactites. If the droplet falls to the floor and evaporates there a stalagmite could grow upwards from the cave floor.
The limestone that makes up these cave formations is known as "travertine" and is a chemical sedimentary rock. A rock known as "tufa" is a limestone formed by evaporation at a hot spring, lake shore, or other area.
Composition of Limestone
Limestone is by definition a rock that contains at least 50% calcium carbonate in the form of calcite by weight. All limestones contain at least a few percent other materials. These can be small particles of quartz, feldspar, clay minerals, pyrite, siderite and other minerals. It can also contain large nodules of chert, pyrite or siderite.
The calcium carbonate content of limestone gives it a property that is often used in rock identification - it effervesces in contact with a cold solution of 5% hydrochloric acid.
Varieties of Limestone
There are many different names used for limestone. These names are based upon how the rock formed its appearance or its composition and other factors. Here are some of the more commonly used.
Chalk: A soft limestone with a very fine texture that is usually white or light gray in color. It is formed mainly from the calcareous shell remains of microscopic marine organisms such as foraminifers or the calcareous remains from numerous types of marine algae.
Coquina: A poorly-cemented limestone that is composed mainly of broken shell debris. It often forms on beaches where wave action segregates shell fragments of similar size.
Fossiliferous Limestone: A limestone that contains obvious and abundant fossils. These are normally shell and skeletal fossils of the organisms that produced the limestone.
Lithographic Limestone: A dense limestone with a very fine and very uniform grain size that occurs in thin beds that separate easily to form a very smooth surface. In the late 1700's a printing process (lithography) was developed to reproduce images by drawing them on the stone with an oil-based ink and then using that stone to press multiple copies of the image.
Oolitic Limestone: A limestone composed mainly of calcium carbonate "oolites", small spheres formed by the concentric precipitation of calcium carbonate on a sand grain or shell fragment.
Travertine: A limestone that forms by evaporative precipitation, often in a cave, to produce formations such as stalactites, stalagmites and flowstone.
Tufa: A limestone produced by precipitation of calcium-laden waters at a hot spring, lake shore or other location.
Fossils
On EarthCache location, you can find not only nice example of sedimentary rock limestone, but also nice examples of fossils. What are fossils, anyway? Well, they are anything that provides evidence of life in past ages. That evidence of life in past ages can come in two types. It can be either direct evidence or indirect evidence of past life.
Direct evidence of life are fossils of hard body parts of organisms. They can be fossilized bones or shells in case of animals. Or it can be fossilized wood or leaves in case of plants. In some cases, the entire organism can be fossilized, together with both soft and hard parts. Example of such fossils are insects trapped in amber or mammoths frozen in ice.
Indirect evidence of life are trace fossils. They are various footprints, trails, marks that were left by organisms and then fossilized. Coprolites (fossilized poo) is also one example of trace fossils.
Classification
Two major classification schemes, the Folk and the Dunham, are used for identifying limestone and carbonate rocks.
Folk classification
Robert L. Folk developed a classification system that places primary emphasis on the detailed composition of grains and interstitial material in carbonate rocks. Based on composition, there are three main components: allochems (grains), matrix (mostly micrite), and cement (sparite). The Folk system uses two-part names; the first refers to the grains and the second is the root. It is helpful to have a petrographic microscope when using the Folk scheme, because it is easier to determine the components present in each sample.
Dunham classification
The Dunham scheme focuses on depositional textures. Each name is based upon the texture of the grains that make up the limestone. Robert J. Dunham published his system for limestone in 1962; it focuses on the depositional fabric of carbonate rocks. Dunham divides the rocks into four main groups based on relative proportions of coarser clastic particles. Dunham names are essentially for rock families. His efforts deal with the question of whether or not the grains were originally in mutual contact, and therefore self-supporting, or whether the rock is characterized by the presence of frame builders and algal mats. Unlike the Folk scheme, Dunham deals with the original porosity of the rock. The Dunham scheme is more useful for hand samples because it is based on texture, not the grains in the sample.
To get the log permission, please answer the following questions:
1. Walk around Church and try to describe the texture and color of the limestone at Bell Tower wall
2. Is this limestone:
a) marine forming environment (explaine)
b) evaporative forming environment (explaine)
3. Is this limestone:
a) biological (explaine)
b) chemical (explaine)
4. Why Dunham’s classification is better than Folk’s classification?
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
