Basalt quarry, Weitendorf, Wildon, Leibnitz District, Styria, Austriai

Regional Level Types
Basalt quarry	Quarry
Weitendorf	Municipality (Former)
Wildon	Municipality
Leibnitz District	District
Styria	State
Austria	Country

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A quarry in andesitic basalt. Famous for nice chalcedony, aragonite, and zeolites (e.g., ferrierite-Mg). One may also find fossils like Turritella, Athleta, and Tibia dentata at this quarry.

Located about 1.5 km west of Weitendorf (west of Wildon and around 17 km south of Graz).

The Weitendorf basalt quarry is a quarry in the market towns of Wildon and Dobl-Zwaring in the Austrian state of Styria. The basalt deposit goes back to the Weitendorf volcano, a middle Miocene shield volcano. It gained fame as a mineral deposit and the location of numerous fossils. Parts of the quarry have been designated as a natural monument since 1985.

The quarry is located in the lower Kainachtal at the southern end of the Kaiserwald. The upper edge of the quarry directly on Weitendorferstrasse (L603) is at an altitude of 305 m above sea level on the left bank of the river. At this point, the valley bordered on the south by the quarry bar (369 m) — before its mouth into the Grazer Feld — has a geologically caused narrowing compared to the wide Kainachboden upstream. The eponymous town of Weitendorf, an independent municipality until the end of 2014, belongs to the market town of Wildon and is located a good 1 km east of the basalt quarry. About 700 m northwest of the edge of the quarry is the town of Steindorf, whose name is probably related to the basalt deposits. The state capital, Graz, is around 19 km away.

Around 18 million years ago, the Styrian Basin began to subside as a result of tectonic processes. As the subsidence progressed, the water of the Paratethys entered the basin from the southeast, and a bay with active volcanism was formed. Earthquakes and hot springs that appeared on the seabed allowed glowing magma to reach the earth's surface through fissures and cover the seabed around Weitendorf and Wundschuh over an area of ​​10 km² with a basalt blanket up to 40 m thick. The volcano, whose existence was first suspected in the 1830s, was only active for a short time and recorded few eruptions. As in Eastern Styria, the crustal thinning on the edge of the Pannonian Basin and the simultaneous uplift of the Alps are assumed to be the trigger. With the help of radiometry, an age of 14.5 to 15 million years was determined, and the type of shield volcano was determined based on the thin lava, similar to the Hawaiian volcanoes. A consequence of volcanism is the recognized healing spring, Sauerbrunn, near Hengsberg.

Strictly speaking, the Weitendorf basalt is a potassium-concentrated basaltic trachyandesite (shoshonite, field S2 in the TAS diagram). This dark gray to black igneous rock forms the lower two-thirds of the quarry wall and partly shows a columnar separation; the surface is spherically weathered to a depth of 2 to 3 m. The hanging wall is formed by blue-gray marls and sands from the Lower Badenian, which in turn are overlaid 4 to 5 m thick by the ice age gravel and clay of the Kaiserwald terrace. Beneath the basalt is a layer of fossil-bearing clay marl from Lower Baden, which was first exposed when the quarry floor was lowered in the 1950s.

Finds of particularly beautiful and colorful minerals, as well as rare fossils, brought the Weitendorf volcano international fame among scientists and mineral collectors from the early 20th century.

Due to the rapid solidification of the lava underwater and the resulting gas seal, geodes were created in the basalt, which are characterized by a rich mineral content. Crystals of various carbonates as well as some silicon dioxide modifications, sulfides, and rare zeolites formed on the walls from aqueous mixed phases. Different colored calcites and aragonites over 10 cm long in conjunction with chalcedony and/or quartz crystals were of interest, as were citrine-colored quartz (colored by sepiolite fibers), banded agates, and intense blue-colored crusts of CT opal with small pyrite crystals scattered thereon. The latter were given the name "Weitendorfer Sternenhimmel" ("Weitendorf Starry Sky") by collectors. The minerals hyalite, clinoptilolite, and harmotome, as well as — in microscopic size — deep cristobalite, pseudobrookite, garnet, malachite, brochantite, and antlerite, were found less frequently.

In the middle Miocene, the area between Weitendorf, Pöls, Preding, and Groß Sankt Florian presented itself as a tropical lagoon that was shielded from the open sea by the Central Styrian threshold. This created a habitat for mussels, snails, crabs, and sea urchins. Over 100 different species have been identified in the clay marls of the quarry, of which the tower snail species, Turritella badensis, appears in a rock-forming horizon that is up to 50 cm thick. The long-beaked snail Tibia dentata and the winged snail Strombus schröckingeri could only be found in Weitendorf and Wetzelsdorf throughout Austria. In addition, a tooth discovery was used to identify the basking shark species Otodus megalodon, which is over 15 m long. The fossil finds enabled a biostratigraphic classification of the rock layers in the Lagenid zone of the Badenian (Florian strata). They also provided evidence of the connection between Paratethys and the Indian Ocean, where the closest relatives of the fossilized species live today.

Finds of spindle whorls prove that the Weitendorf basalt deposit was actively used as early as the Neolithic period. From the 16th century onwards, regulated quarry operations took place, with the Weitendorf basalt initially serving primarily as building and paving stone. While in the surrounding area the foundation of Wildon Castle was built from the stone, in Graz it was in demand as a particularly abrasion-resistant pavement.

In 1943, the quarry was the largest basalt quarry in Austria. In 1977, the Leibnitz district administration approved an in-house diesel tank system and issued regulations for employee protection. There were serious explosions in the quarry twice: in 1972, the explosives depot containing 227 kg of explosives and over 600 detonators exploded for unknown reasons; in 1984, two burglars were killed while trying to open the factory safe using a welding torch and oxygen bottles. In the same year, the designation of the quarry as a natural monument was discussed. The community of Weitendorf saw this as an opportunity to prevent the city of Graz from having a planned landfill but demanded that the quarry operations be maintained as a condition. In March 1985, the BH finally placed 0.6 hectares in the southern mine area under monument protection, whereby it was decreed that the fossil-bearing clay marls must not be buried in order to remain accessible. The Graz magistrate's appeal against the decision was dismissed.

Situation 2016: Fossils occur again in a freshly excavated spot, within dense clay.

Since 2019, the quarry has been owned by Ecker-Eckhofen Rohstoffverutilization GmbH after it was sold by the city of Graz. Weitendorf basalt is used as fine chippings, asphalt aggregate, and particularly weather-resistant hydraulic stone.

Situation April 2024: Scheduled to be transformed into a solar power plant.

Situation September 2025: Quarrying still under way, with lots of fossils exposed in the "Deep Hole".

Commodity List

This is a list of exploitable or exploited mineral commodities recorded at this locality.

Mineral List

30 valid minerals.

Rock Types Recorded