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Abstract
Quartz crystals with some impurity ions can absorb energy from ionizing radiation, e.g. gamma rays. This absorption of energy can influence its optical and electromechanical performance, thermal characterisation, as well as its color. Natural gem-quality dark brown (morion type) smoky quartz specimens from the Aydin region were investigated using the chemical analyses (XRF, ICP-AES), microscopical observations (PM), X-ray diffraction (XRD), spectroscopic evaluationsinfrared vibration (IR), simultaneous differential thermal and thermo gravimetric analysis (DTA/TGA), radioluminescence (RL), and Thermoluminescence (TL), to reveal and discuss their physic-chemical and geochemical formation conditions.
One of the most important gem material of Turkey, smoky quartz crystals, werestudied for color saturation from the mineralogicalgenetic view point. Color formation in the smoky quartzes is due to the color centres which are produced in the result of exposing to mainly gamma irradiation of some substituted impurity elements in SiO4 tetrahedral in the quartz lattice. When the optical absorption graphics (OA) comprising the ultraviolet, visible, and near-infrared regions and the impurity elements (ICP and AES) are evaluated collectively, four main absorption bands are related to producing the color centres Accordingly, in the morion type smoky quartzes, the absorption peaks at 375 nm, 450 and 490 nm, 620 nm and 730 nm is due to Al3plus, Ti4plus, Fe2plus, Mn2plus ions respectively.
Radioluminescence (RL) graphics can be used as an effective method showing the color centres exposed to irradiation in the mineral lattice. The RL graphic of natural smoky quartz crystals displays that the most affected impurity elements after exposing to additional gamma irradiation in the crystalline structure are Fe and Al elements with 3plus valance value substituted for Si4plus in the smoky quartz silica lattice. Accordingly, Fe3plus ion representing the RL band at 600 nm, Al3plus ion representing the RL band at 720 nm, Mn2plus ion representing the RL band at 385 and 410 nm, and Ti4plus ion representing the RL band 495and 510 nm.
The IR transmission stretching curve of smoky quartz samples were recorded on standard axes in the measured range (4.000 and 400 cm minus1). Accordingly, the some collective and crosswise vibration bands of the smoky quartz samples were compared with peaks of the colorless quartz sample.
Thermal behaviors of the smoky quartz samples were investigated using the thermograms of the simultaneous differential thermal and thermogravimetric analyses (DTA/TGA) from room temperature up to 1400 degrees Celcius to observe the changing ratios in their water contents and enthalpy during dehydration.
