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Rabstejn - roofing slate / Rabstejnska bridlice

A cache by Skleba Send Message to Owner Message this owner
Hidden : 6/22/2009
Difficulty:
2 out of 5
Terrain:
2 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:


Rabstejn - roofing slate

The name of the small town of Rabstejn blends with the term Rabstejn roofing slate. Roofing slates are fine-grained to compact well-cleavable rocks, of a dark grey colour. They have dull up to silky lustre on their foliation planes.

The first mentions of slate quarrying come from the privilege of King Ladislaus Jagiellon from 1514. Besides the locally very widespread use of slate as a roof covering, it was used on large constructions (Karlštejn Castle, chateau in Chyše, chateau in Manetin etc.)

            In the area of Rabštejn, roofing slates occur in the space of the eastern fringe of the town. Their thickness varies from a few metres up to 100 m; the length of individual stripes is very variable as well. The largest two locations of roofing slate are situated to the south of Rabštejn. These locations are uncovered very nicely in steep slopes of the deep-cut valley of the river Strela and used to be extracted in several quarries. The number of stripes of roofing slates rises to the north of the town but at the expense of their thickness and stability, so they are no longer so useful for quarrying. Three quarries were opened in a hillside on the right bank of the Strela below the chateau; the largest quarry was on the left bank of the river.

Actual quarrying was carried out in a primitive manner. Holes were drilled by hand for charges of black powder which was used to disintegrate the rock. Quarried pieces of the rock were split to smaller plates, of which suitable, well-cleavable material was handpicked. The material was then split by means of a chisel into small plates with a thickness of ca. 5 mm. The shape of the covering was traced on the plates according to a template, and individual shapes were cut on wooden sawhorses by means of special scissors. An opening for attaching the board was cut through by a pick hammer. In spite of the fact that several shapes of covering were produced, even of various sizes so that the area of the quarried plate was utilized as much as possible, the waste was considerably high, up to 75-80% of the material quarried.

The last producer of slate roofing was the national enterprise Rudné doly in Príbram, which renewed mining operations for a short time in 1969-1972. Mining was concentrated to the north of Rabštejn and was not too effective.


            Uncovered in quarries are lithologically monotonous, weakly metamorphosed Proterozoic slates (chlorite up to biotite zone) of the Kralupy-Zbraslav group of the Barrandien area on their transition into rocks of the Teplá crystalline complex. With their overall character they correspond to dark grey up to black chlorite-sericite phyllites. Besides sericite and chlorite, biotite and albite also occur locally. Parts with coarser grains contain abundant clastic relicts of psammitic material (quartz, feldspars). Leucoxene, graphitic pigment, in places also tourmaline, pyrite, calcite and apatite occur in accessory quantity.

            In some sections the rocks described acquire the character of phyllitic (roofing) slates, forming the transition element between unmetamorphosed and weakly metamorphosed sediments and chlorite-sericite phyllites. These are characterized by flat, unfolded foliation planes with dull up to silky lustre and by the rarer presence of secretion quartz veins. As a rule, they are fine-grained up to compact, of a dark grey colour, with a greenish shade. From a microscopic point of view, they are characterized by light and dark banding. Predominant in lighter bands is quartz; darker sections contain predominantly micas accompanied by graphitic pigment. Both authigenic and allothigenic quartz (grains with a size of around 0.2 mm), feldspars, sericite, chlorite and lightly greenish biotite have their share in the mineral composition of phyllitic slates. The association of accessory minerals is represented by abundant ilmenite, titanite, graphite, tourmaline, and zircon.

 

To log this earthcache find, you must fulfill the following requirements:

 

1) Estimate the thickness reached by the two largest locations of roofing slate and find out what separates them.

2) Find out in what direction the quarries were opened towards the position of roofing slate layers.

3) At the information board find out what area is covered by 1q of roofing slate (in m2).

4) Add your photo and a photo of a GPS device at the information board 

 

The answers to the questions please send via e-mail in my profil, thanks.

 

 

       

 

 

 

 

Rabstejn - pokryvacska bridlice

Jmeno mestecka Rabstejna splyva s pojmem rabstejnska pokryvacska bridlice. Pokryvacske bridlice jsou jemnozrnne az celistve dobre stipatelne horniny, temne sede barvy. Na plochach bridlicnatosti maji matny az hedvabny lesk.
Prvni zminky o lamani bridlice pochazeji z privilegia krale Vladislava Jagelonskeho z roku 1514. Mimo mistne velmi rozsirene pouzivani bridlice jako stresni krytiny, byla pouzita na velkych stavbach (Karlstejn, zamek v Chysi, zamek v Manetine aj.)
            V oblasti Rabstejna se vyskytuji pokryvacske bridlice v prostoru vychodniho okraje mestecka. Jejich mocnost kolisa od nekolika metru az do 100m, rovnez delka jednotlivych pruhu je velmi promenna. Nejvetsi dve polohy pokryvacske bridlice probihaji jizne od Rabstejna. Tyto polohy jsou velmi pekne odkryty ve strmych stranich hluboce zariznuteho udoli Strely a byly tezeny v nekolika lomy. Severne od mestecka se pocet pruhu pokryvacskych bridlic zvetsuje, avsak na ukor jejich mocnosti a stalosti, takze pro tezbu nejsou jiz tak vyhodne. Na pravem brehu Strely, pod zamkem, byly ve strani otevreny tri lomy, nejvetsi lom byl na levem brehu reky.
            Vlastni tezba se provadela primitivnim zpusobem. Rucne se navrtavaly otvory pro naloze cerneho prachu, jimz se rozpojovala hornina. Vylamane kusy horniny se stipaly na mensi desky, z nic se vybiral vhodny, dobre stipatelny material. Ten se pak dlatem stipal na desticky o sily asi 5mm. Na desticky se obkreslil tvar krytiny podle sablony a na drevenych kozach se pak zvlastnimi nuzkami rezaly jednotlive tvary. Otvor pro upevneni tabulky se prosekaval pokryvacskym kladivkem. Presto, ze se vyrabelo nekolik tvaru krytiny, a to jeste v ruznych velikostech, tak, aby bylo co nejvice vyuzito plochy vylomene desticky, byl odpad znacne velky, az 75-80 % vylamaneho materialu.
Poslednim vyrobcem bridlicove krytiny byl narodni podnik Rudne doly v Pribramy, ktery kratkodobe obnovil tezbu v letech 1969 – 1972. Tezba byla soustredena severne od Rabstejna a nebyla prilis efektivni.

 


V lomech jsou odkryty litologicky monotonni, slabe metamorfovane proterozoicke bridlice (chloritova az biotitova zona) kralupsko-zbraslavske skupiny barrandienu na jejich prechodu do hornin tepelskeho krystalinika. Svym celkovym charakterem odpovidaji tmave sedym az cernym chlorit-sericitovym fylitum. Vedle sericitu a chloritu se lokalne objevuje i biotit a albit. Zrnitostne hrubsi casti obsahuji hojne klasticke relikty psamitickeho materialu (kremen, zivce). V akcesorickem mnozstvi vystupuje leukoxen, grafiticky pigment, misty i turmalin, pyrit, kalcit a apatit.
            V nekterych partiich nabyvaji popisovane horniny charakteru fylitickych (pokryvacskych) bridlic, tvoricich prechodny clanek mezi nepremenenymi a slabe premenenymi sedimenty a chlorit-sericitovymi fylity. Tyto jsou typicke rovnymi, nezvrasnenymi, matne az hedvabne lesklymi foliacnimi plochami a vzacnejsi pritomnosti sekrecnich kremennych zilek. Byvaji zpravidla jemnozrnne az celistve, tmave sede barvy, s nazelenalym odstinem. Mikroskopicky se vyznacuji svetlym a tmavym paskovanim. Ve svetlych prouzcich prevlada kremen, tmavsi partie obsahuji prevahu slid doprovazenych grafitickym pigmentem. Na mineralnim slozeni fylitickych bridlic se podili autigenni i alotigenni kremen (zrna o velikosti kolem 0,2 mm), zivce, sericit, chlorit a svetle zelenavy biotit. Asociaci akcesorickych mineralu reprezentuje hojny ilmenit, titanit , grafit, turmalin a zirkon.
 





K zalogovani earthcache je nutno splnit nasledujici ukoly :

1) Zjistete jake mocnosti dosahuji dve nejvetsi polohy pokryvacske bridlice a zjistete cim jsou oddeleny.
2) Zjistete v jakem smeru se lomy otviraly vuci poloze vrstev pokryvacske bridlice.
3) U info tabule zjistete jak velkou plochu pokryje 1q pokryvacske bridlice ( v m2)
4) K logu pripojte fotografii Vas a pristroje GPS u informacni tabule.

Odpovedi me zaslete pres profil na muj email, diky.

 

 

       

 

       
 

 

 WWW pocítadlo teto stranky ríka, ze jste navstevnik cislo

 


 

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