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.
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