Due to the extent of the empire’s territory, the remains of the Achaemenid stone pillars have been registered in different parts of Iran. The remains of this architectural style can be seen in the monumental set of Pasargadae, Persepolis., Naqsh-e Rostam, Lidoma and Tomb-e Bot in Fars Province, the remains of Shush in Khuzestan Province, and stone works of Ecbatana in Hamedan, Rivi Palace in Northern Khorasan Province, and Achaemenid palaces in Borazjan region in Bushehr province. The rock mining of these monuments was recognized as local. However, in Boushehr Province, two ancient mines of Pouzepalangi Rahdar and Tang-e Gir of Borazjan Region have been named. The maximum extraction and application of the crème color stones from the Puze- Palangi mine were registered from the palaces of the Borazjan Region. However, for the geological structure of the black-gray stone of Acamenian palace in Charkhab of Borazjan, samples of this type of stone were extracted from Charkhab palace. These samples were compared with the gray-black samples of the Bardak-e Siah and Sang-e Siah Palaces of Borazjan. With the petrographic studies of thin sections obtained from the palaces and chemical analysis of XRD and XRF, the structural process of the gray-black samples of the Achaemenid palaces of the Borazjan region entered a new stage. The results of the petrography studies indicate that the gray-black stone samples of Charkhab palace corresponded to the sample of Sang-e Siah Palace and Badak-e Siah, considering the microsprite and sprite background, and the few amount micrite as well as the layered structure. Also, the analysis of the analytical samples of XRD and CRF of these stones indicates that the samples of Charkhab Palance and Sang-e Siah are the same. Given that no trace was found in the mining for the gray-black stones in Boushehr Province so far, it can be then claimed that these stones were extracted from a non-local mine. Keywords: Borazjan, Charkhab Palace, Bardak-e Siah Palace, Sang-e Siah Palace, Petrography, XRD, XRF. Introduction The coasts of the Persian Gulf, especially the ports of Bushehr and Borazjan in the golden age of Elam, i.e., the late 2nd millennium BC, has been one of the important centers of trade and the interface between the sea route of Shush and India. The fertile and tropical areas of Dashtestan were among the areas where the Achaemenid dominated shores and benefited from the proximity to the sea. They provided places for themselves in these areas so that they could spend the winter there. The building of Charkhab Palace in Borazjan is known as the winter palace of Achaemenid Cyrus due to its great similarity with the private palace of Cyrus in Pasargadae. Research Questions and Hypotheses: The main questions of research are as follows: What is the structure of black-gray stones used in the Achaemenid architecture of Borazjan palaces? What is the structural relationship between black-gray stone in the Achaemenid palaces of Borazjan (Charkhab, Bardak-e Siah and Sang-e Siah)? Based on current studies, what opinion can be expressed about the mines of Borazjan Achaemenid palaces? Research Method: Petrography and analytical methods of XRF and XRF were used to the geological structure of the gray-black stones of the stone pillars of Charkhab Palace in Borazjan. In the meantime, using the research method thin-walled structure to observe the minerals and adopting the samples were done with the OLYMPUS BX51 polarizing light transmission microscope, made in Japan, with the capability of filtering light in the XPL mode of the analyzer and emitting polarized light. XRD experiments to identify and detect the crystalline phases forming in the study samples and qualitative and semi-quantitative determination of crystals by powder method (with Cu) target radiation lamp with a maximum potential difference of 40 KV and maximum current intensity of 30 mA, fixed sample and Needle detector) was performed on three samples of historical palace stones in Bim Gostar Taban laboratory in Tehran. The results were analyzed by High Score Plus software. XRF experiments were performed to identify and quantify the constituent elements of study samples of Achaemenid palaces by powder method and with the model device: PW1410 Manufactured by PHILIPS Netherlands in Bim Gostar Taban laboratory in Tehran on the same three samples. Research Background Borazjan city is located 67 km from Bushehr and 226 km from Shiraz. Due to the discovery of a piece of a stone pillar base when digging a water canal in Borazjan in 9171, the General Directorate of Archaeological Research of Iran assigned Dr. Ali Akbar Sarfaraz to explore the site in which this work was discovered. Dr.Ali Akbar Sarafraz was the head of the Iranian Archaeological Board in Bishapour at that time. Therefore, archeological operations began in this ancient area, and at the end of the one season of the excavation, the main form and structure of the columned hall were manifested. In a study entitled “Spatial analysis of the Achaemenid palaces in Borazjan” the appearance, location, and objects obtained from these sites have been discussed. Petrography Results The gray-black stone of all three Achaemenid palaces of Charkhab (CH1, CH2, and CH3), Bardak-e Siah (BS1), and Sang-e Siag of Borazjan (SS1) are calcareous and boiled in contact with 0.1 normal hydrochloric acids. These carbonate rocks have a microsparite texture to sparite, and are micrite to a small amount, and have few quartz grains. XRD Analysis of Gray-Black Stone Samples of Achaemenid Palaces in Borazjan Region The spectrum of gray-black stones of the Achaemenid palaces of the Borazjan region, which includes the samples of Charkhab Borazjan (CH3), Bardak-e-Siah (BS1), and Sang-e-Siah (SS1), the matching of the spectra of the same limestone is observed. However, based on the peak intensity of calcite in the samples of Charkhab Palace (CH3) and Sang-e Siah (SS1), which shows 11000, are placed in one group. Also, the sample (BS1) with a peak intensity of calcite over 14000 is observed separated from the group. XRF Analysis In the analysis of the black-grey stones of the Achaemenid palaces, the sample of grey-black stones of palaces has been compared as only the samples of palaces are available. Also, the possible mine of the black-grey stones has not been reported in Boushher Province so far. Accordingly, the oxide of the main elements, such as SiO2, CaO, P2O5, TiO2, and MgO, represents particular values in the table. These values are approximately close to each other in the sample of the grey-black stones of the Achaemenid palaces. Therefore, they are considered an appropriate indicator of similarity. Graphs of oxide values of SiO2, P2O5, TiO2, CaO, and MgO of the samples are consistent. Also, the accordance of the oxide values of the mentioned elements, the values of the secondary elements (in terms of ppm) of the gray-black stones of Charkhab (CH3), Bardak-e Siah (BS1), and Sang-e Siah (SS1) rocks are observed. Analysis and Discussion Using the laboratory and scientific methods and comparing the results of this paper with the results of the papers on Pasargadae and Persepolis, the relationship between the sources of extraction of gray-black stones of the complex of Achaemenid monuments in Borazjan Region of the Fars province mines, Majdabad mountain mine in particular, around the Perspolis and Sarpaniran and Ahmadbegi Mines in Pasargadae is rejected. The presence of several large pieces carved from this type of stone in the east of the Achaemenid palace of Charkhab Borazjan confirms that Charkhab palace was in the process of construction. However, these stones which have been left on the ground two hundred meters east of the palace, are reasons for the existence of a stone-cutting workshop of Charkhab palace or another building that has not been excavated yet. Conclusion Studies on the gray-black rocks of Achaemenid palaces show that mining traces or mine exposure of this kind of stone have not been seen or reported in the region. Therefore, it seems that these mines were not local, and the stones were supplied from other sources. Also, the hypothesis based on that the grey-black stone mines might have been local depends on the more extensive field studies in the future.