The limestone of Ançã Formation: a heritage stone from Portugal

Ançã limestone is one of the most widely used geological formations as building stone throughout history in Portugal, and it can be recognized in many places throughout the country and abroad. The middle Jurassic Ançã Formation was deposited between the Bajocian and the Bathonian at the Lusitanian Basin (central west of Portugal), and it outcrops in Cantanhede municipality, about 25 km northwest of Coimbra. This formation is approximately 250 m thick and it is constituted at the base by layers that reach ≈2 to ≈3 m of greywish micritic limestone, slightly marly, changing to light gray and yellowish to white laterally. It is followed by creamy white to micritic limestones, in layers from ≈0.5 to ≈1 m thick.

Hard limestone types of low porosity and high strength are exploited on three quarry zones located in the Ançã-Portunhos-Outil region, which have many processing and carving workshops. The current annual production of Ançã limestone is ≈8000 m³, which is a distinguishing element of civil construction in the entire area. In addition, the Stone Museum of Cantanhede is a place of learning that promotes activities related to building stones.

The limestone of Ançã Formation is a strong candidate for “Global Heritage Stone”. This stone fits the proposed designation as it has been used since prehistoric times and its greatest use occurs since the 14^th century. It has been widely used in important buildings, tombs and monuments of Coimbra. Some historically remarkable examples include the “Porta Especiosa” in the Old Cathedral, the entrance of Santa Cruz Church and the tomb of the first king of Portugal, D. Afonso Henriques.

The University of Coimbra – Alta and Sofia have been granted UNESCO World Heritage status in 2013, and all associated buildings, monuments and pedestrian streets are constructed from heritage stones. Coimbra University is located on a hill overlooking the city. It has colleges that grew and evolved over more than seven centuries within the old town, with the Ançã limestone as the main building stone. Notable buildings include a number of 16^th-century colleges, the Royal Palace of Alcáçova, which has housed the University since 1537, the Joanine Library (early 17^th century), and the 18^th-century Botanical Garden, as well as the large “University City” created during the 1940s.

The importance of Coimbra’s emblematic heritage makes it necessary to protect Ançã limestone and its historical quarries. Given the ongoing transformation of the dimension stone industry, it is important that urban planners and policymakers responsible for cultural heritage work in tandem with needs of the traditional quarry extraction areas.

As may be deduced from the foregoing, Ançã limestone meets all the requisites for a GHS nomination. Its designation would contribute to raising awareness of its essential importance for regional economic growth, while furthering more efficient use of this dimension stone as a restoration material.

Fundação para a Ciência e a Tecnologia I.P. of Portugal supported this study with the CEECIND/03568/2017, UIDB/00073/2020 and UIDP/00073/2020 projects of I & D unit Geosciences Center (CGEO).