Gemology and industrial minerals

Abstract The Manshad skarn is exposed 40 km south of Yazd and on the western margin of the Central Iranian subcontinent in the granodiorite stock intercalation with Cretaceous carbonate units. In this skarn system, the mineral assemblage of wollastonite, clinopyroxene, spinel, clintonite, phlogopite, garnet, tremolite-actinolite, vesuvianite, epidote, calcite and quartz is seen. Spinel is one of the gem minerals of this skarn system, which is green, automorphic and isotropic and, based on the results of electron micrograph analysis, has a hercynite composition. Mineralogical studies and paragenetic relationships of minerals confirm the formation of the Manshad skarn through several stages of metamorphism. In the early stages of metamorphism, clinopyroxene was formed as a result of the intrusion of silica-rich solutions into the carbonate host rock, and then spinel formed independently or from acidic and cationic leaching of pyroxene, providing a source of aluminum for the formation of clintonite, phlogopite, garnet, and vesuvianite. The source of a skarn is a skarn of polygenetic origin.

Abstract    Kerman province is located southeast of Iran and have Sanadaj – Sirjan, Uromieh – Dokhtar, central iran and Makran geology zone. Sanandaj – Sirjan have gemstone in metamorphic rocks, include types garnet, kordierite and andalosite in hornfels, shist and skarn. Uromieh – Dokhtar zone there is mineralization precious and semi-precious stone in metamorphic and igneous rock. Semiprecious mineralization in igneous rocks with silicification, andesite and granite origin, skarn metamorphic rocks whithin garnet. Semi-precious mineralization in central Iran zone, around of volcanic and intrusive igneous rocks and related hydrothermal activated. The northern part of Makran zone has ophiolite melanges rich in ultramafic rocks with precious and semi-precious minerals such as spinel, titanium, serpentine, olivine. Most of the gem stones of Kerman province are from the silica family (quartz, agate, jasper, etc.) in the vicinity and with the origin of andesites.

Abstract The art of gemology and gem cutting is highly appreciated and appreciated today and has become a lucrative career for geology graduates and other people of all levels of education. Taft County, located 20 kilometers west of Yazd, is rich in gemstones due to the intrusion of Shirkuh, Ali Abad, Khezr Abad and Adar Bolandan granite masses into the sedimentary rocks of the region, especially the Cretaceous limestone formations of the Taft Formation, along with volcanic formations. It is one of the areas with potential for precious and semi-precious gemstones in Yazd Province.

Abstract The Kushak lead and zinc deposit is located within the Esfordi Formation, which consists of a series of volcanic-sedimentary sequences of Infracambrian age. Variscite is observed as cross-veins within the pyrite ore of the Kushak deposit, in both open-pit and underground mines. Based on XRD and electron microscopy studies, it was determined that the formula of this mineral is AlPO4.2H2O. This mineral is formed by the action of phosphate-containing oxidant waters on aluminum-bearing rocks, especially shales.

Abstract Moissanite (SiC) or natural silicon carbide is a rare mineral. This paper is focused on the first & preliminary research on this mineral in south of Iran which is find in Hormoz formation. The preparation of thin sections is for petrology are done with instruments without synthetic SiC. It is proved that natural moissanites occurred in geological samples. The host rock is a metasomatic (silicified) rock. The tiny terrigenous particles (micrometer size) show carbon blur color with high relief in plane polgrized light. By use of FESEM analysis (EDS) it is revealed the chemical composition of SiC.

Abstract Gem-quality transparent to semi-transparent crystals of demantoid from Bagh Borj, were examined by different conventional and advanced gemological methods. (XRD, EDXRF, XRF, Raman).
   This study focuses on garnets sourced from Bagh Borj (Kerman), using standard and advanced gemological methods as well as chemical analyses, XRD, energy dispersive X-ray fluorescence (EDXRF) and Raman spectroscopy.
   The results of XRF showed that the content of Cr and V in most samples is high, with some samples containing a Cr₂O₃ content up to 0.032%. This suggests that Cr is the primary chromogenic element of Bagh Borj area demantoid, but the role of vanadium cannot be ignored.
   Raman spectroscopy revealed absorption peaks near 868 cm^-1, 816 cm^-1 and 517 cm^-1, associated with (Si–O)_Str vibrations (Si–O stretching vibration), and absorption peaks are displayed near 358 cm^-1, related to the rotation of SiO₄–R(SiO₄)^4-, and the peaks near 517 cm^-1 are related to (Si–O)bend vibrations (Si–O bending vibration). Additionally, related absorption peaks near 164 cm^-1 are attributed to the translation of SiO₄–T(SiO₄)^4-, and absorption peaks near 226 cm^-1 are associated with the translation of X²⁺–T(X²⁺) (X²⁺ represents divalent ions).
   The high pressure mineral assemblage (amphibolite, garnet-amphibolite, kyanite-garnet-amphibolite, hornblendite and epidote-amphibolite), indicated that the studied garnet from serpentinite was formed through high pressure metamorphism, during the subduction zone serpentinization.