FLINT, DIFFERENT AND VARIABLE

The results obtained by optical microscopy with polarised light, and via X-ray diffraction analysis (XRD), showed there to be great variation in the composition of Casa Montero’s siliceous rocks. This is reflected in the difference in their colour and density. Three basic types were recognised: flint, opal and opaline flint (mixtures of opal and quartz). Their textural and structural characteristics are influenced by the rocks in which they were included, as well as the aging of opal, which transforms it into quartz.

The aging that the siliceous rocks of Casa Montero underwent sets them apart from those of other siliceous formations in the greater Tagus Basin. This may have been what attracted people to the area over 7000 years ago and begin mining.