A contribution by Ana Maričić*

*University of Zagreb – Faculty of Mining, Geology and Petroleum Engineering, Pierottijeva 6, 10000 Zagreb, Croatia, [email protected]

Have you ever observed the stone on the streets that you walk on? Or stone on the monuments, statues and buildings? Did You ever think where did it come from? Have you ever wondered why used stone materials are so decorative? Natural building stone represents mineral raw material that is used in architecture, sculptures, statues, monuments, cladding facades, paving streets, masonry walls, cemeteries etc. For this type of stone, its decorativity is very important. Why is that? The main purpose of the natural stone is to be the protective and decorative coating of the buildings. Therefore, decorativity is one of the main factors that influences the price of stone on the market. But what influences its decorativity? Decorativity is influenced by colour and different mineral composition, fossil content and different patterns. Many Croatian natural stone varieties are very decorative, and we will present a few examples, including Kirmenjak Avorio, rudist limestones Veselje unito and Rasotica, foraminiferal limestone Istranka and Lithothamnium limestone. Details about the above-mentioned Croatian varieties could be found in a paper by Fio Firi and Maričić (2020).

The most famous and decorative high-quality stone variety from Croatia is Jurassic limestone Kirmenjak Avorio or Pietra d’Istria exploited in Istria. Because of its quality and decorativity it has been used in many buildings in Venice, Italy. Decorativity of the stone is influenced by its colour that reminiscent of ivory but also by seams that are called “stylolites” along which two parts of the rock entangle in one another (Fig. 1).

Kirmenjak Avorio stone with visible “stylolitic” seams

Many different varieties of rudist limestones are excavated in Croatia with Upper Cretaceous Veselje unito (Veselje means Joy in English) from the Island of Brač being the most famous. Due to its white colour, it is often miscalled “Brač marble”, although it is in fact limestone. Its decorativity originates from numerous fossil bivalves called “rudists” that were completely crushed and uniformly scattered in the stone. Many monuments and sculptures are made of this stone because such variety is suitable for sculpting and carving (Fig. 2). Students at Stonemasonry school on the Island of Brač use this material for their sculptures.

Many sculptures and ornaments are made of Veselje unito variety – a window on the Stonemasonry school Island of Brač

One more decorative rudist limestone variety from the Island of Brač is dark brown Upper Cretaceous limestone called Rasotica. The stone is very decorative due to its dark colour with numerous rudist bivalves. Due to its dark colour, this stone is better to be used on indoor surfaces since the dark colour of stone gradually fades in outdoor areas and the stone loses its decorativity (Fig. 3).

Rasotica limestone with rudists from the Island of Brač

Another dark brown variety from Croatia is Paleogene limestone Istranka (Fig. 4), named after the peninsula Istria where this stone was exploited. Stone is very decorative due to its colour and many visible sections of foraminifera. As Rasotica, it is better to be used indoors to save its colour stability.

Dark brown foraminifera limestone Istranka

Important and decorative stone varieties are Neogene yellowish Lithothamnium limestone (Fig. 5) and Litavac which are autochthonous to Zagreb and the most commonly used stones throughout the city. The name of the stone derives from the red coralline algae which are the main component of the stone. In addition, stone has many large pores that are evenly distributed, and numerous visible fossils (e.g., bivalves, echinoderms).

Stone blocks made of Lithothamnium limestone

All specific decorative features of a particular stone can be enriched by processing the stone surfaces like polishing. Decorativity of stone is one of the main evaluation criteria but it must not be the only criteria for its selection. When stone is used in some construction, it is important that it does not change its properties and appearance with time. Because of that, other stone properties and durability should also be taken into consideration.

Now that you know something about the stone varieties in Croatia, in the next number of the ENGIE Magazine we will take you on a geological walk through the Capital of Croatia, the City of Zagreb, where mentioned varieties can be seen on many buildings, streets and squares…

Reference:

Fio Firi, K., Maričić, A., 2020. Usage of the Natural Stones in the City of Zagreb (Croatia) and Its Geotouristical Aspect. Geoheritage, 12:62, https://doi.org/10.1007/s12371-020-00488-x

This article has been published in the April 2021 edition of the ENGIE Magazine.