La utilización del leucogranito turmalinífero de Martinamor en los monumentos de Salamanca y Alba de Tormes

Abstract

The Martinamor quarries, consisting of tourmaline leucogranites, have been documented as a source material for many post-medieval historical buildings of Salamanca and Alba de Tormes. The granite itself outcrops as a thin, shallowly northward-dipping sheet-like intrusion, belonging to a phase-3 Variscan antiform. Apart from its short distance from the city of Salamanca, several significant criteria can be considered to account for the successful use of the Martinamor granite: 1) petrographic, such as its quartz- and alkali feldsparrich composition, scarce biotite and scarce Ca-rich minerals, as well as a microscopic-scale inequigranular interlobate texture with a strong quartzfeldspatic interlocking; 2) geochemical, showing high-silica contents; and 3) physical-mechanical properties, having low porosity values (0,75-0,86%) and low capillary absorption and imbibition coefficients. All these features result in a hard and consistent stone that has been used for more than 400 years (1515-1932) in Salamanca and Alba de Tormes. Three periods have been distinguished: 1) an initial period, in which the architect Juan de Álava may have introduced the stone for transitional Gothic-Renaissance buildings; 2) a main period, linked to the Lisbon earthquake (1755 A.C.), making reinforcement of the New Cathedral necessary, together with the construction of magnificent new buildings of Neoclassic style; and 3) a period of functional use, in which Martinamor stone has been systematically used for the foundations of new buildings as a result of urban alignments during the nineteenth century. Also, in the late nineteenth and early twentieth century Martinamor granite was used in many historic buildings as ashlar material where a replacement has been required. In order to recognize the reposition blocks several criteria have been proposed: a) remains of abandoned wedges at the top of the blocks; b) the diversity of the nature of the blocks in the same course; c) mismatching of courses; and d) old photographic documentation. Its use in steps and pavements from the sixteenth century onwards was also due to its hardness and consistency. Finally, an aesthetically based use seems to have played a role, taking advantage not only of the enclavefree homogeneous fabric and hand-scale overall equigranular texture, but also the non-conspicuous light colour of the stone, the former quality being exploited for Renaissance and Neoclassic style buildings, whereas the latter one proved to be a suitable quality for block reposition in Plateresque-style monuments.