Silicon DOI 10.1007/s12633-016-9432-x ORIGINAL PAPER Chromatic Classification of Ouargla (Algeria) Dunes Sand: Determination of Main Compositions and Color Causes, by Using XRD, FTIR and XRF Naouia Mahdadi 1 · Sma¨ ıl Chihi 1 · Hamza Bouguettaia 1 · Samiha Beddiaf 1 · Mohammed La¨ ıd Mechri 1 Received: 30 August 2015 / Accepted: 28 March 2016 © Springer Science+Business Media Dordrecht 2016 Abstract In the present work, a manually chromatic clas- sification of Ouargla dunes sand has been carried out. According to its visual color, eight chromatic types of sand have been obtained: transparent (yellow, orange and red), and opaque (white, milky, gray, black and red). According to the main chemical compositions of sand, both XRD and FTIR have divided the chromatically sorted sand into three groups: quartzite (transparent samples), calcareous (milky, gray and black opaque samples) and calcareous quartzite (white and red opaque samples), without possibility of dis- tinguishing between the sorted samples. FTIR spectroscopy has shown all functional groups and vibration modes in these samples. XRF spectroscopy has shown that sand grain colors are closely related to the main compositions as well as the impurities. It has also been shown that transparent samples contain more than 92 % of quartz (SiO 2 ). The redness of transparent samples is proportional to iron (Fe) impurities. It has also been shown that milky, gray and black opaque samples contain more than 55 % of calcium oxide (CaO). The milky color is due to magnesium (Mg) and sulfur (S), whereas the blackness is due to iron (Fe) and manganese (Mn). Both white and red opaque samples  Sma¨ ıl Chihi chihism@yahoo.com Naouia Mahdadi mahdadi.naouia@univ-ouargla.dz; mahdadina@gmail.com 1 Facult´ e des Math´ ematiques et des Sciences de la Mati` ere, D´ epartement de Physique, Laboratoire de Rayonnement et Plasmas et Physique des Surfaces (LRPPS), Universit´ e de Ouargla, Ouargla 30000, Algeria contain approximately equal concentrations of quartz and calcite, whilst the redness refers to the high concentration of iron (Fe), whereas the whiteness is due to the presence of magnesium (Mg). Keywords Dunes sand · Chromatic classification · XRD · FTIR · XRF · Quartz · Calcite 1 Introduction Algerian Sahara has huge quantities of sand dunes. These are among the important natural resources which may be exploited in different fields. Sand is known as a raw mate- rial which some industries are based on [1–4]. Sand is used either in its natural form or after various processes, in order to be ready for usage [3, 4]. Sand can be used for water fil- tration [5, 6] and building [7, 8]. Extracted quartz from sand can be used in glass, optics [1, 2, 9] and to extract silicon, that is utilized in semiconductors and nano industries. Sand types vary according to their resources that are based on their interaction with natural factors such as heat, wind and humidity. Sand is a mixture of different size grains ranging from 0.02 to 2 mm [10]. Most sands are composed of quartz (SiO 2 ) and feldspar (AlSi 3 O 8 ), which are the most abundant of earth’s crust [11, 12]. Sand contains consid- erable concentrations of aluminum oxide (Al 2 O 3 ), calcium carbonate (CaCO 3 ) and iron(III) oxide (Fe 2 O 3 ), as well as small amounts of impurities. The most salient visual feature of sand is its grain colors, which indicate that these grains have different composi- tions. For example, pure quartz is colorless, but it may look green when containing nickel traces, and red when having iron impurities [13].