# Compositional Analysis of Chalcopyrite Using Calibration-Free Laser-Induced Breakdown Spectroscopy
## 1 Introduction  
Chalcopyrite belongs to an economically important class of minerals and looks like gold, it is also known as Fool's Gold. It is considered as one of the primary and major sources of copper (Cu)production globally [1]. It is a brass-yellow colored sulfide mineral with chemical formula (CuFeS\({}_{2}\)), and it crystalizes into a tetragonal structure, having metallic luster and high specific gravity [2]. It mainly occurs in metalliferous veins and metamorphic and igneous rocks. Chalcopyrite is among I-III-VI2 type semiconductors and owing to its structure, face-centered tetragonal lattice, it is considered one of the most stable minerals [3]. The superior conduction properties of copper makes it an essential material for the fabrication of wide range of electric equipments such as wiring and motors, as well as craft tools and weapons. Copper concentrate and slag produced during the process of copper extraction from chalcopyrite contain precious elements such as silver (Ag) and gold (Au), which further elevates the economic value of this mineral [4]. Copper is also playing a key role in the development of renewable non-conventional sources of energy such as solar energy. Materials from the chalcopyrite family have found very important applications in the development of high efficiency solar cells because of their high internal quantum efficiencies and adsorption coefficients [5]. Chalcopyrite-based solar cells have achieved a great landmark of the highest power conversion efficiency of about 22.3% [6]. The determination of the elemental composition of a mineral is of prime importance for the identification, classification and extraction of minerals. For this purpose, various elemental analysis techniques, destructive or micro destructive, such as energy dispersive X-ray spectroscopy (EDX), atomic absorption spectroscopy (AAS), X-ray fluorescence (XRF), inductively coupled plasma mass spectrometry (ICP-MS), electron probe micro analyzer with wavelength dispersive spectrometers (EMPA-WDS), and Raman spectroscopy are deployed. With theoretical and experimental advances, the laser-induced breakdown spectroscopy (LIBS) technique has been developed into a powerful alternative and widely applied analytical technique. A few advantages of LIBS over the conventional analytical techniques can be listed, such as simultaneous identification of elements, requirement of nominal or no prior sample preparation, in-situ analysis, capability of analyzing liquid, gas and solid samples, fast response, identification of lighter elements, element identification in real time and low detection limit down to ppm or even better [7; 8]. One of the fascinating features of LIBS is its use in the laboratories, industry, and in the field for close-in analysis or at standoff distances for both qualitative as well as quantitative elemental analysis [9]. The cost of a LIBS system depends on the choice of its components such as lasers, spectrometers and the optics but its overall cost is lower than aforementioned analytical techniques [9]. Gaining these benefits makes LIBS a preferable detection method for the field samples. LIBS involves generation of a transient plasma plume on surface of the target sample by a focused laser radiation of sufficient fluence. The excited atoms in the plasma de-excite to their ground levels by emitting characteristic optical radiation. The spectral line of optical emission from the plasma is unique for each compositional element of the sample and the measurement of this emission spectrum reveals the identity of the corresponding element [10; 11]. Geo-materials in large numbers including carbonates, rocks and metals from mixed mineral groups, such as feldspars, beryls, and pyroxenes, were comprehensively studied by employing the LIBS technique [12; 13; 14; 15]. For the purpose of quantitative analysis, calibration and calibration-free LIBS methods were employed as the standard tools for reliable identification of field samples.