Periodico di Mineralogia

Crystal-chemical effects of heat treatment on Cr- and V-bearing Ca-dominant green tourmalines (fluor-uvite, magnesio-lucchesiite)

Peter Bačík — 2024-09-13

We present a detailed study of thermally driven changes in Ca-dominant tourmaline using Electron Probe Microanalysis (EPMA), powder X-ray diffraction (PXRD), Raman and optical absorption spectroscopy (OAS). The KEN samples from Kenya (5 crystal fragments) can be classified as fluor-uvite, while TAN from Tanzania (5 fragments) is dominantly magnesio-lucchesiite. Tourmaline samples were thermally treated in air at 700, 800, 900, and 1000 °C. Both sets were green with different hues, TAN with a bluer hue than KEN. After heating, no significant visual changes were observed in TAN samples until breakdown at 1000 °C. In KEN, after heating at 700 °C, the yellowish tint disappeared. Raman spectroscopy showed no significant changes after heating. Raman luminescence spectra revealed the sharp intensive band located at 680-684 nm, accompanied by a broad band between 690 and 900 nm in all samples heated up to 900 °C. OAS spectra look similar, with two major bands in blue and yellow to red regions. In TAN, the bands shift with the increasing Cr/V from 608 to 604 nm. In KEN with low Cr/V, the band is located between 613-617 nm. After heating at 1000 °C, both samples broke down with different associations: cordierite/indialite and glass from magnesio-lucchesiite, and cordierite/indialite, mullite-like phase, spinel and glass from fluor-uvite. There was a difference in volume between the samples; both samples expanded in volume, but the KEN sample expanded more with larger pores likely resulting from a higher proportion of volatile phase in this sample.

Origin of graphic texture by magma mixing-induced undercooling in the Borjuri diorite pluton, Mikir Massif, Northeast India

Tribujjal Prakash — 2024-11-20

Graphic intergrowths from the Borjuri diorite pluton in the Mikir Massif of Northeast India were investigated to reflect on the role of magma mixing in their formation. The work presented discusses how magma mixing triggers an abrupt change in liquidus temperature (undercooling), driving the formation of graphic intergrowths. Previously, fractal dimensions were utilised in experimental work to understand the involvement of undercooling in graphic texture formation. The present study follows the earlier documented experimental work and puts forward a new approach, as it employs fractal and lacunarity calculations in natural systems (i.e., natural diorite from the Mikir Massif). The fractal and lacunarity calculations presented in this work demonstrate the complexity of graphic intergrowths, in order to qualitatively assess the relative degree of undercooling. Undercooling, resulting from the rise in liquidus temperature, was achieved due to loss of volatiles or devolatilization during magma mixing. Observed disequilibrium textures such as rapakivi, anti-rapakivi, skeletal amphiboles, acicular apatite, biotite clots, dendritic and zoned plagioclase, provides a reliable explanation for an origin linked to magma mixing, further providing a different perspective for the growth of such graphic intergrowths. Signatures of magma mixing have been reported from numerous Pan-African felsic plutons in the Assam-Meghalaya Gneissic Complex. Considering the regional viewpoint and the textural signatures observed in the diorites, magma mixing could be the only plausible explanation for the formation of the diorites.

Mineralogical and Technological Characteristics of Volcanic Rocks around Nevşehir Province of Türkiye

Mustafa Albayrak — 2024-11-15

In this study, rock samples were taken from study area, Tuzköy, Gülşehir, Avanos and Ürgüp Units, Nevşehir Province (Türkiye) and their mineralogical and petrographical properties were investigated. In addition, preliminary technological tests of some samples have been made. Physical and chemical analysis, thin section, XRD, SEM-EDX and firing tests were performed on the test samples. Original color and condition of these samples and their water dispersion, plasticity, reaction with dilute acid, firing color and condition were investigated to determine their potential to use as ceramic raw material. The rocks were found to be calc-alkaline, rich in silica and high potassium peralumina, with rhyolitic and dacitic character. Zeolite minerals were identified, including erionite, which poses a health risk. While erionite-free samples exhibited colors and properties suitable for the ceramic industry, their presence necessitates caution in industrial use due to health concerns. As a result, some samples (Nev 25, Nev 31, Nev 43, Nev 47, and Nev 48) are suitable for use at temperatures below 1150 °C while some others (Nev 44, Nev 54, and Nev 61) at temperatures below 1300 °C. In the investigated areas, the distribution of erionite minerals should be identified and mapped, and further detailed investigation of non-erionite-bearing areas in line with the study’s objectives is considered important from an economic geology perspective.

A comprehensive assessment of huntite ore formation

Adil Ozdemir — 2024-10-03

The Çameli basin (Southwestern Turkey), economically important exploitable huntite ore deposits are located a basin. The huntite deposits in the basin are the largest known deposits in worldwide. In this study, new huntite outcrops were identified in northeastern of the basin and the samples from the outcrops were analyzed. The results of X-ray diffraction (XRD) and X-ray fluorescence (XRF) analyses were combined and comprehensive interpreted with literature studies. In the samples, average 70.4% huntite, 15.2% dolomite, and 14.4% larnite minerals were detected. Major element analysis showed an average of 28.62% MgO, 18.78% CaO, and 44.09% loss on ignition. Loss on ignition (LOI) values are 38.85-47.53%. CO2 values are 44.77% and 45.14%. In literature, huntite mineral is theoretically predicted to contain 34.15% MgO and 15.88% CaO. In the samples, the MgO values are 26.00-31.77% and CaO values are 18.50-19.66%. SrO values are 0.11-0.30%. Sr concentration in huntite indicates that Ca-rich karst waters play a role in huntite ore formation. The low SrO contents sign that the formation of huntite in Çameli basin is a result of the mixture of Mg-rich saline waters and small amounts of Ca-rich karstic waters from the basement. The results of the analyses, when compared with previous studies on huntite minerals, it is understood that all values are quite close to each other. Therefore, Mg- and Ca-rich solutions that precipitated during huntite ore formation played a role in releasing Sr on aragonite, which then precipitated together with Ca and Mg. This suggests that huntite is a product of the late meteoric phase and the primary mineral is aragonite. The results of this study indicate that huntite are an ore by carbonization of the altered serpentine according to SiO2-CaO-MgO contents.