## 1 Introduction  
Basalt is the most widespread magmatic or igneous effusive rock. With andesite, another type of volcanic rock, it makes up almost all, about 98%, of the rocks made up of the lava that erupted on the Earth's surface and was then subjected to a process of crystallization. Generally, when not greatly weathered, basalt has colorations that from dark gray can tend to black [1]. For several years, it has been employed in casting procedures to produce ceramic plates and panels for architectural purposes [2]. In addition, fused basalt coatings for iron pipes show an extremely high abrasion strength in manufacturing operations [3]. Basalt is also used in many countries in the construction of highway and airport pavements [4], and it also finds application in organic farming, in the form of micronized rock flour, to revitalize and nourish soils and plants that have lost fertility, such as intensive and extensive farming that deplete soils of natural elements [5].  
Furthermore, fragmented basalt aggregates, which are compact, finely grained, very dark green or black rocks produced when melted lava from the depths of the Earth's crust ascends and crystallizes, are also recognized as a natural resource for the manufacturing of cheap and eco-friendly construction materials with acceptable strength and durability features, well suited to the framework of sustainable development [6,7]. In detail, the partial replacement of Portland cement with basalt aggregates in concrete, when available, can lead to a more cost-efficient solution [8].  
Basaltic rock in Italy can be found close to the Mt. Etna volcano (eastern Sicily, Southern Italy) [9], the edifice of which grew on a sedimentary substrate more than 1.5 km thick [10]. The origin of Mt. Etna's magmatism is probably related to extensive melting of the mantle, according to what is reported in [11].  
In the present paper, a multi-technique approach including the use of High-Purity Germanium (HPGe) \(\gamma\)-ray spectrometry, Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and X-ray diffraction (XRD) was employed with the aim to evaluate the radioactivity (radium-226, thorium-232, potassium-40 and caesium-137) and the heavy metals (arsenic, cadmium, copper, mercury, nickel, lead, antimony, thallium and zinc) content of the investigated basalt aggregate for concrete, picked up in a surrounding area of the Mt. Etna volcano [12], and to relate the natural radionuclides' specific activity to its mineralogical composition.  
Furthermore, in order to assess any possible radiological hazard for the population, the calculation of the alpha index (I\({}_{\alpha}\)), the radium equivalent activity (Ra\({}_{\text{eq}}\)), the absorbed \(\gamma\)-dose rate (D) and the annual effective dose equivalent outdoor (AEDE\({}_{\text{out}}\)) and indoor (AEDE\({}_{\text{in}}\)) was performed [13, 14, 15]. Of note, in Italy, the current legislation states that building materials or additives of natural igneous origin are subject to radiometric checking before being placed on the commercial market [16].  
Finally, with the aim to estimate the level of environmental chemical pollution by the heavy metals, the Enrichment Factor (EF), Geo-accumulation Index (I\({}_{\text{geo}}\)), Contamination Factor (CF) and Pollution Load Index (PLI) were assessed [17,18].