Geoparque Mundial UNESCO

Nº08 – Hornos de la Calera Alía

Geoparque Villuercas > Nº08 – Hornos de la Calera Alía

LOCATION AND ACCESS

The hamlet of La Calera is a dependency of the village of Alía. It can be reached by travelling some 10 km on a local road that leaves Alía to the north.

About six kilns still stand in two groups in varying states of preservation. The first of these near the hamlet on the road to Navalvillar de Ibor consists of three kilns, one of which has virtually been destroyed, and a fourth at some distance. The second group of kilns is further away and is in relatively good condition; as with the previous group, there are calcareous rock quarries in the vicinity. 

ATTRACTIONS OF THE VISIT

This small settlement owes its origin to the quarries and kilns for the obtaining of lime that are situated in the surrounding area. These were used in different periods; in particular they kept the nearby Monastery of Guadalupe supplied with lime during its construction in the 14th century.

Next to the kilns lie the quarries from which were extracted the calcareous rocks (limestone and massive recrystallised dolomites) which consist of calcium and magnesium carbonate. The extraction front of some 3 m in height and 25 m in length can be seen; it covers a wide surface of these rocks to almost 100 m2.

The kilns are practically uniform in size, with a diameter of some 2.5 m and a height of some 3-3.5 m. Stones of limestone (calcium carbonate, CaCO3) were placed inside them on a bed of evergreen oak firewood. The kiln was lit in order to subject them to calcination for three days at an approximate temperature of 700º-900ºC and convert the calcium carbonate of the limestone into quicklime (calcium oxide, CaO). The quicklime was put out by adding water to obtain a white paste that was used mixed with sand as a joining element in the construction of stone walls or bricks and for whitewashing walls.

GEOLOGICAL INTERPRETATION

Structurally these calcareous outcrops are located on the flanks of the great Ibor-Guadalupe anticline, which today has been completely worn down by erosion, in aligned sections of massive appearance but reduced thickness. They are separated from each other in the shape of a rosary; they have generated small projections as a result of differential erosion since these carbonated rocks are harder than the surrounding slates and chalco-schists. 

They originate in the organic or biochemical deposits of flat seaweed and stromatolites that were laid down in shallow marine environments of the Ediacaran period (+ 540 m.y.).

Around the quarries the predominant rocks in the valleys are Precambrian shales and greywackes and on the hillsides the limestones, chalco-schists, and shales of the Ediacaran period, while the Armorican quartzites of the early Palaeozoic are situated on the crests where they have been fragmented to form the typical pedreras of the nearby Sierra Palomera.

In the surrounding area we can also observe some layers of conglomerates of quartz boulders and a calcareous matrix with an average thickness of some two metres, which have been worn down by erosion to take the form of large boulders that have become isolated halfway up the slopes.