Cieszynit
A. Dorda
An old and common truth says that everybody who wants to erect a permanent and safe structure must build it on stable and secure ground, on a hard base, i.e. a rock. Cieszyn was erected in exactly the same way and the rock on which the foundations of the town were laid was called cieszynit. Nobody should be surprised at such a name since a rare plant, characteristic of this region, was named cieszynianka, (every spring the town is embellished with its green and yellow flowers) and cieszynkas was the name given by the townspeople of the 16th and the 17th centuries to the beautifully embellished guns they went hunting with.In reality only some buildings in Cieszyn could be raised on cieszynit because the ground in this region is composed of various kinds of rocks. The ground in Cieszyn Silesia is like a layer cake with many layers placed on top of each other. However, they are not laid evenly as in a cake. Instead, they lay slantwise and in different parts of Cieszyn Silesia different rocks can be found at ground level. Those “layers” are called nappes and are tectonical units. In the Cieszyn region the ground is formed by a nappe which was called, of course, cieszyńska nappe. It is composed of three layers of sedimentary rocks which were formed in the process of sedimentation, i.e. depositing of a rock-forming material. The rocks were formed in the early Cretaceous period which started 135 million years ago. The lowest layer is composed of lower shales, called Cieszyn shales (the reason for which, by now, should be obvious to everyone), also known as Goleszów marls. Goleszów is a village near Cieszyn in the vicinity of which there used to be quarries where the above mentioned shales were excavated and then added, in minute amounts, to the cement produced in the Goleszów cement plant. They are bituminous rocks, from yellow and grey to dark grey, and the thickness of this layer is about 300m. On lower shales there is a layer of tabular organic limestone, 150 m thick, and of whitish, yellowish or greyish colour. Also these limestones were, in the past, exploited in numerous small and big quarries, their location ranging from the foot of Mała Czantoria to Goleszów. At present these limestones are mined in a quarry in Leszna Górna. On top of the limestones there is a layer of Cieszyn upper shales, 300 m thick, of dark, sometimes steel-grey colour; their structure resembles shale sandstone.
In sedimentary rocks of Cieszyn nappe we come across “wedged” seam veins of abyssal magma rocks, i.e. the rocks that were formed in the process of magma cooling. These intrusions occur most often in Cieszyn upper shales. The names of these rocks sound extremely serious and scientific, e.g. diorytoidy, gabroidy foidowe, or pikryty. Their regional names, which are well-known, acknowledged and commonly used in geology, are cieszynits (cieszynity).
The thickness of the cieszynit veins ranges from as little as several centimeters to several meters and their length reaches a few hundred meters.
Cieszynits occur in numerous different forms and they differ from each other in their chemical and mineralogical specification. The main components of cieszynits are amphiboles, pyroxenes, plagioclases, minerals related to feldspar, biotites, and olivines. These names sound mysterious and incomprehensible to somebody whose main contact with geology and rocks is accidental and restricted mainly to occasional stumble over a stone while taking a stroll. These terms imply various silicates of magnesium, iron, calcium, and sodium, as well as alumino-silicates of sodium and calcium. They occur in different magma rocks. They have various colours, ranging from white, yellow, grey, green, russet, reddish russet to black and they form granules, sticks, needles, plates, lamellae and other forms of crystals.
Cieszynits have different colours (ranging from whitish grey, greyish green to completely black) and different structures; the latter depends on which rock-forming mineral or minerals that is/are prevalent. In thicker veins one can usually see thick granules, with the predominance of lighter plagioclases. In fine-grained cieszynits, on the other hand, it is dark elements that are preponderant. The dark minerals decay quite easily and this means that the cieszynits that have been exposed for a long time to the process of erosion, resemble loosely bound conglomerates that can be literally crumbled in the hand. The age of the cieszynits is undetermined, they probably come from the middle Cretaceous period, so they are probably younger than the sedimentary rocks in which they are found. Cieszynit was distinguished and described by Ludwig Hohenegger, the author of the first detailed geologic map ( published in 1861) of the Duchy of Cieszyn.
On Cieszyn Plateau cieszynits are found mainly in the surroundings of Cieszyn (Boguszowice and Kalembice), between Puńców and Mnisztwo, in Rudowa, Zamarski and near Iskrzyczyn, Wiślica and Grodziec. Sometimes they are small bare rocks, outcrops, but one can see cieszynits more often in old quarries that are no longer worked. At present cieszynits are of no economic importance, although not longer than a few decades ago they were quarried – and used, mainly as material for road building, in quite numerous places of the Cieszyn Plateau. One of such places is, perhaps, the so-called Ondraszkowa Dziura, a small cave, in the “Kopce” nature reserve in Marklowice. Although the rock is interesting and rare, there is only one quarry, on Goruszka Hill, in Grodziec Śląski, that has been preserved and received the status of a monument of nature (established in 1958).
In Cieszyn there are numerous places where one can see cieszynits but two places have been selected as worth preserving and protecting, mainly for scientific and educational reasons. They are: a cieszynit outcrop near Kręta street, under a fly-over at Graniczna street, and a disused quarry on the Kalembianka in Majowa street.
The cieszynit outcrop near Kręta street is situated in the lower part of a slope of a broad valley, the Olza valley, in the neighbourhood of the estate at 12 Kręta street. Not far from there are pillars supporting the fly-over at Graniczna street (i.e. a border bridge) and a bunker, i.e. a military shelter that originates from the 1930’s. The outcrop is visible and easily accessible to anyone who is interested. The wall of the outcrop is 25 m long and it reaches a maximum height of 2,5m in its middle part. In this place cieszynit is coarse-grained or medium-grained and its colours vary depending on the local changes in proportions between dark and light minerals. In its middle part the magma rock has recently been exposed and its black, elongated bars – hornblende crystals, pyroxenes, as well as lighter plagioclases and minerals closely related to feldspar are all perfectly visible. In marginal parts of the wall the cieszynit is weathered and therefore the rock is, at some places, covered with crustification containing iron oxides that came into being as a result of the decomposition of dark minerals. Due to a resolution passed by the Municipal Council in Cieszyn in 2002 the outcrop was given protected status as a so-called place of documentation. Another outcrop that is situated nearby, within 12 Kręta estate, also looks very attractive and is perfectly visible from the street.
The second place with cieszynit which has been acknowledged as worth preserving is a former quarry in the neighbourhood of Majowa street, not far from 64 estate. The quarry cuts its way into a wooded slope just above the Kalembianka, on its left bank. It has the shape of a regular amphitheatre, 25m/25m in size, and it opens in the direction of west and north-west. The highest wall (in the eastern part) reaches a height of 17 m, counting from the bottom of the quarry. By that wall the quarry is covered with a big talus of stone “rubble”. The cieszynit vein is exposed on the eastern wall and in the lower parts of the south-eastern wall. In the lower part there are dark and fine-grained cieszynits, on which lie layers of dark chert, rust-coloured. The next layer is that of slightly metamorphized mudstone. Chert and mudstone are rocks that have been transformed due to sedimentary magma rocks (cieszynit) forcing their way into the layers. In the upper part of the wall one can see Cieszyn upper shales, of light colour. They are silt or loam and silt shales. Around the quarry there is a forest growing on dry ground, with hornbeam trees, maple trees (Acer campestre) and oak-trees, as well as a few other species that are protected, i.e. hepatica, asarum, primrose and viburnum (Viburnum opulus).
Because of their rare occurrence, cieszynits, as well as cieszynianka wiosenna, should be considered as the most interesting curiosities of nature in Cieszyn.