Gemology and industrial minerals

Abstract    An innovative method was developed to evaluate the feasibility of combining artificial intelligence (AI) and advanced methods to standardize high-quality turquoise from the Neyshabur mine. Initially, conventional methods in gem identification and artificial intelligence were used to identify turquoise, then advanced gemological methods were used for standardization.
   The gemological characteristics of turquoise were determined with the help of digital image analysis and artificial intelligence (AI). This method relies on image processing by artificial intelligence (AI). 1600 digital image series of 18 samples from different areas of the Neyshabur turquoise mine were prepared and transferred to the database. The accuracy of turquoise gemstone identification using this method was 94%. With the help of XRD analyses, mineral identification, crystal structure determination, phase determination, and crystal particle size determination were possible. The average particle size of lower quality turquoise was 201.2 °A and gem quality turquoise was 137.9 °A calculated by Debye-Scherer formula. The identified Raman peaks are in the ranges of 200 cm^1-, 400 cm^1- and 1000 cm^1-. The peaks at 1031 cm^1-and 1036 cm^1-are related to phosphate vibrations, but the peaks in the range of 1-200 cm^1- are probably related to water or hydroxyl vibrations in the structure. Turquoise samples examined by SEM showed that low quality turquoises contain Si and Ca elements in addition to their main elements.
   Comparison of RAMAN, XRF, XRD and SEM analyses of turquoise from Neyshabur mine with turquoise from other regions of the world showed that turquoise from Neyshabur mine has its own unique XRD pattern that is significantly different from that of turquoise from other regions of the world. These differences are also clearly visible in RAMAN, XRF and SEM data analyses. This research showed that the turquoise gemstone from the Neyshabur mine (of gem quality) should be introduced as the world's standard turquoise reference.

Abstract Shirmaghz bentonite deposit is located close to Shirmaghz village, 51 km north east of Ghaen city and 35 km south of Geysur village, Eastern Iran, in central Iran geological zone and north part of Lut block subzone. According to the field evidences, microscopic studies and based on ICP-MS chemical analysis of trace and rare earth elements (REEs), the parent rocks of Shirmaghz bentonite deposit are mainly acidic to intermediate volcanic rocks such as dacite and andesite belongs to Calc-Alkaline magmatic series along with pyroclastic tuffs. minor amounts of Basalt are also present. ASTER Satellite Images processing determined distribution of clay minerals in the investigated area.
Mineralogical analysis on Shirmaghz bentonite samples done by optical microscopy and XRD. Chemical analyses were performed by XRF and ICP-MS. The XRD results confirmed that smectite group minerals mainly of beidellite and Na-montmorillonite are the major clay minerals of the investigated area. Furthermore, The Chemical analyses of major oxides by XRF, indicates the mean values of Na₂O is 2.21% and CaO is 0.77%. The chemical analysis results also shows that the high percentage of SiO₂, (65-70 %) and moderate amonts of Al2O3, (11-13.5%). These chemical analysis indicates that Shirmaghz bentonite deposit is Na type. The higher amounts of SiO₂ suggests the hydrothermal origin of this deposite which were resulted from alteration of volcanic and pyroclastic rock units that are directly in associate with fault zones.
Based on physical, chemical and industrial properties of Shirmaghz bentonite deposit, the most important industrial applications of this bentonite is in casting and iron pelletizing industries.

Abstract So far, no documented geological evidence of diamond potential has been observed in the Iranian crust. However, geological formations and assemblages in Iran exist that allow for the possibility of diamonds. This study examines geological formations and assemblages with diamond potential for future geological explorations.
Among the geological formations and assemblages with potential diamond content, kimberlites and lamproites containing diamonds have not been reported in Iran. Nevertheless, geological assemblages in Iran with potential diamond potential include eclogites and ophiolites suites with diamond-bearing potential, ultra-high-pressure (UHP) metamorphic rocks, and meteorite impact sites.
Diamond-potential eclogites are characterized by high concentrations of magnesium-rich garnets (pyrope or magnetite-rich almandine) and amphibole, with the presence of coesite, orthopyroxene, clinopyroxene, Phlogopite, and sometimes spinel. Important locations for eclogite formation in Iran, such as the Shanderman eclogite (northwestern Iran) and the Sistan region eclogite (eastern Iran), with their mineralogical, petrological, and geochemical characteristics, can be further explored.
The diamond-bearing peridotites of Iran, with the presence of lower-crust and upper-mantle minerals and the unique chemical composition of the rocks in these areas, such as high concentrations of platinum group elements (PGEs), are valuable sets for exploring diamond-bearing peridotites. Among them, garnet-bearing (with chromium-rich spinels) deep-mantle peridotites containing high-magnesium olivine suites, orthopyroxenes along with clinopyroxenes containing high Mg (especially with the presence of metasomatic minerals such as Phlogopite, apatite, and amphibole), can be excellent evidence of diamond formation potential. The peridotite suites of Iran with specific geochemical characteristics, containing lower Al and Ca harzburgites but high Mg forsterite olivines, along with chromium-rich spinels and lower REE and Os concentrations than primary mantle, are also valuable sets to mention.

Abstract Three different Varieties of corundum (sapphire) occurrences in Iran is investigated. They are out cropped in three different geologic environments including: A) syenitic pegmatites of Alvand batholite (Hamadan area). B) Metamorphic rocks (Metabauxite) of Central Iran and C): Advanced argillic alteration related to epithermal systems. They are characterized mainly by following mineral assemblages:
A: Corundum + k- feldspar + quartz, tourmaline + muscovite + spinel
B: Corundum + diaspore + chlorite + ilmenite
 
C: Quartz + sericite

In pegmatites of Alvand batholite the metasomatic process have been engaged in sapphire in association with spinel formatiom. There are likely desilification processes for spinel- corundum generation. Mineralization which is formed as phenoblasts in association with spinel.
Corundum veinlets which are developed in metabauxide show most gem quality.
In Alvand argillic alteration the desilicification prosses are provided the suitable conditions for corundum depositions.

 Pegmatite and metabauxite occurrences are characterized by gem quality corundum. Some UV-VIS spectroscopic data of those sapphires are also presented in the paper.

Abstract The mineral corundum (a type of blue sapphire) is found in the central section of composite aplite-pegmatite dikes (pegmatites with a combination of syenite), associated with the Elund plutonic suite in the Hamadan region. All aplite and pegmatite samples are highly aluminum-rich and are of type S granite. Chemical earth studies indicate an increase in Al2O3 and K2O with a decrease in SiO2 in corundum-bearing pegmatites. The increase in the Al2O3/TiO2 ratio indicates that element Al in the high-temperature fluid containing alkaline elements was extracted and enriched in the final metasomatic fluids by forming polymers such as Na-Al-Si-O from the melt. The chemical composition matching of corundum in the Hamadan region on the diagram separating types of primary corundum (FeO - Cr2O3 - MgO - V2O3) versus FeO + TiO2 + Ga2O3) confirms its metasomatic origin and direct crystallization from alkaline melt for the formation of this deposit.

Abstract Petrographic and ore mineralogy have been done on chondrite samples which is found by meteorite hunters from Central Iran Deserts (Kavirs). The thin and polish samples studied by polarizing microscope (Gemology and Meteorite lab Geology Dept. University of Isfahan). The following mineral assemblage mainly have been detected:
Olivine + orthopyroxene + opaque minerals (troilite + Fe oxyhydroxide + Fe- Ni metal)
Chondrites are in milimeter size and are characterized by variety of microstructures (texture) including: porphyritic, microgranular, radial and barred
By using FESEM the mineral chemistry of components are determined studing the textures of chondrules could help to interpret the petrologic processes engaged in their formation

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.