Stebelnata rula / Pencil gneiss EarthCache
Stebelnata rula / Pencil gneiss
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CZ: Earthcache vas zavede k prirodni pamatce Stebelnata rula,
ktera byla vyhlasena v roce 1977 k ochrane unikatniho a svetove
prosluleho naleziste teto zajimave horniny.
ENG:Earthcache will take you to the natural monument Stebelnata
rula (Pencil gneiss), which was established in 1977 to protect
unique and world- famous locality of this interesting rock.
Co
je to rula?
Rula je premenena hornina vznikla plosnym pusobenim vysokeho tlaku
a teploty na jiz drive vytvorene horniny, a to jak horniny vyvrele
(magmatity) nebo usazene (sedimenty). Ruly vznikle z vyvrelin se
nazyvaji ortoruly,
ruly vznikle premenou sedimentu jsou pararuly.
Typicke pro ruly je usporadani do mnoha tenkych rovnobeznych
"vrstev", kteremu se rika bridlicnatost
nebo
foliace.
Co je
to stebelnata rula?
Pokud se v
rule nachazeji tenke, valcovite utvary rovnobezne usporadane, rika
se takove odrude ruly „stebelnata“. Na rozdil od jinych
rul je pomerne vzacna (a taky oku lahodici). Zdejsi stebelnatou
rulu oznacuji pertrografove jako kourimskou. Geologicky tato
hornina patri do oblasti kutnohorskeho krystalinika. Jednotliva
stebla na vychozech, ktere si prohledneme, maji prumer az nekolik
milimetru, stridaji se tmavsi a svetlejsi polohy. Pri letmem
pohledu nam svoji strukturou mohou pripominat zkamenele
drevo.
A jak na odlov
EC?
Zacneme
na WP – zde si muzete prostudovat informacni tabuli.
Doporucuji si zapamatovat, ktere mineraly zdejsi rulu tvori. Rovnez
zde zjistite,zda
tato rula vznikla z vyvrele horniny nebo z horniny usazene (otazka
c.1).Nakouknout muzete za
plot domku, kde na stene lumku zahlednete peknou ukazku
bridlicnatosti. Odkryv je ale na soukromem pozemku, prosim
nevstupujte za branku a neobtezujte obyvatele domu. Stebelnatou
rulu si muzete dosytosti a hezky zblizka prohlednout
na souradnicich EC.
Pote se
vydame k ricce Vyrovce a pujdeme po asfaltove ceste smerem po
proudu. Vpravo po nekolika metrech uvidime lomovou stenu. Zde si
muzete prohlednout cca 7 m odkryteho ruloveho profilu.
Prosim zjistete,
na kterou svetovou stranu se uklaneji vrstvy horniny (otazka
c.2). Zhruba uprostred steny
je vyrazna vrstva, lisici se barvou – otazka mimo soutez: co
toto zbarveni asi zpusobilo?
Po nekolika dalsich
krocich se dostanete na souradnice EC. Zde si muzete zblizka a
detailne prohlednout pekny vychoz stebelnate ruly. V hornine
uvidite vyrazna naruzovela stebla. Vzpomente si, ze kterych
mineralu se zdejsi rula sklada, a odhadnete, ktery
z peti mineralu jmenovanych na informacni tabuli tvori tato
naruzovela stebla (otazka c.3).
A samozrejme dobrovolny ukol – prosim vyfotografujte
sebe ci svoji GPS na vychozich souradnicich ci na WP (prosim
neprikládejte k logu fotografii uobrazující lomovou stenu z
otázky c. 2).
Odpovedi na
otazky mi prosim poslete na e-mail uvedeny v mem profilu. EC si
mužete hned zalogovat, pokud by bylo treba neco vyjasnit, ozvu
se vám.
What
is gneiss? 
Gneiss is a metamorphic rock formed as a result of high pressure
and temperature on already created rocks, both igneous (magmatites)
or sediments. Gneiss arising from igneous rocks is called the
orthogneiss, gneiss
resulting from the transformation of sediment is caled paragneiss. Typical for the gneiss is
organization into many thin parallel "layers", which is called
foliation.
What
is pencil gneiss?
If the
gneiss forms a thin, cylindrical formations, such variety gneiss is
called "pencil gneiss". Unlike other gneisses, this form is
relatively rare (and also eye-catching). Local type of pencil
gneiss is called “kourimska”. Geologically the rock
belongs to the Kutna Hora Crystalline. Each stalk have a diameter
of several millimeters, with alternating darker and lighter
position. At first glance us its structure may resemble petrified
wood.
The Earthcache
tasks:
We will start by WP
– here you can read the information board. You schould
remember, which minerals dorm the local gneiss. You will also find
out here, whether this gneiss was
formed from igneous rocks or sediments. (question 1). You
can peek behind the fence where the quarry wall offers a good
example of foliation. Outcrop is on private property, please
do not enter the gate, and
harass the inhabitants of the house. You will have a good close
look to pencil gneiss at the coordinates of the EC.
Note: Information on the board is
only in Czech. If you do not understand Czech, I like to give you
relevant information in English.
Then we head
toward the river and will go by the asphalt road towards
downstream. Right after a few meters you will see the quarry
wall. Here you can see about 7 meters of the gneiss profile.
To which direction is the rock
strata bowing (question 2) ?
After a few more steps
you will reach the EC coordinates. Here you can examine nice small
outcrop of pencil gneiss. You will see distinctive pink straws.
Which of five minerals, named on
the information board formed these pink straws (question
no.3)?
And
of course the usual optional tasks - please make photo of yourself
or your GPS at coordinates of outcrop or by WP (Please do not take
photo showing the quarry wall from question
2).
Responses to the questions please send to the e-mail listed in my
profile. Do not wait for confirmation and feel free to log the EC.
If it would be needed to clarify something, I will write you.
Additional Hints
(No hints available.)