# Characterization of Talcose Rocks Derived from  
Sperpentiinte--Pilot Study in the Ultramafic Complex of Cabo Ortegal (Spain) for Potential Use and Commercialization  
of water or any sort of organic molecular species between the talc layers. The layers of the structure have almost monoclinic symmetry but the nearly hexagonal rings of oxygen atoms on the surfaces of the layers, formed by the bases of the silica tetrahedral, are partly displaced so that the stack of layers forms a triclinic crystal [3]. Talc is taken as a standard for hardness, having the value 1 on the Mohs scale. Talc exhibits perfect cleavage along a (001) plane of symmetry, yielding flexible, slightly elastic lamellae. Although talc has a marked affinity for certain organic chemicals, it generally has very little chemical reactivity. It is intrusible, inert to acids, and neither explosive nor flammable. Moreover, talc is a non-conductor of electricity and, thus, it is used in the manufacture of high frequency electrical insulators [3]. Regarding the mineral chemistry of talc, only minor differences from the end-member formula Mg\({}_{3}\)Si\({}_{4}\)O\({}_{10}\)(OH)\({}_{2}\) are detectable. Small amounts of Al, Cr, or Ti may substitute Si and small amounts of Mn, Al, and Fe may substitute Mg in the octahedral sites. Very small amounts of Ca, Na, and K may also substitute Mg, but in several cases these elements may represent impurities [3]. Minor amounts of Ni are often found in talc associated with ultrabasic rocks, while ferrous iron was detected in hydrothermal talc. These heavy metal substitutions are of great interest for the scope of this paper. There are detailed descriptions of the igneous and metamorphic rocks that outcrop in the Cabo Ortegal complex, as well as of the petrogenesis of such rocks [1]. Serpentinites were also studied in an attempt to evaluate their quality as ornamental stone, considering that a large part of the heritage of the area was built with these serpentinites, which are transformed into talcose rocks that are locally known as _pedra de toelo_ (and marketed as Verde Tuelo). Usually, talc crystallizes in lamellae and occurs mainly in metamorphosed ultrabasic rocks. However, it also crystallizes in high-grade kyanite-talc rocks and, by the replacement of olivine and tremolite, in siliceous dolomites [4]. It is the major component of economic deposits of steatite or soapstone. To the best of the authors' knowledge, very little has been published on talcose rocks from Cabo Ortegal, probably because their distinction from serpentinite is not very clear and, in the field, it becomes very difficult to distinguish them (Figure 1). Furthermore, the chemical and mineralogical analysis are confusing due to the complicated distinction of mineral phases of the asbestos group using traditional techniques (e.g., petrography, X-ray diffraction). It is worth remembering that the term asbestos refers to a group of minerals including five fibrous amphiboles (amosite, i.e., the fibrous variety of cummingtonite-grunerite; crocidolite, i.e., is the fibrous variety of ribeockite; anthophyllite, actinolite and tremolite) and one fibrous serpentine mineral (chrysotile) [2; 3]. Due to the worldwide economic importance of talc as a raw material [5], the authors consider this publication to be an important step towards spreading knowledge of these rocks in the area of study. This pilot study considers only a very limited number of samples (two, Figure 1) to evaluate whether it is worth extending the study to include more samples and other analytical techniques (e.g., stable isotopes) for a complete characterization.