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Semi-precious stones
Published in Francis P. Gudyanga, Minerals in Africa, 2020
Topaz Al2SiO4(F,OH)2 is a silicate mineral containing aluminium and fluorine. It is colourless and transparent but normally tinted by metal impurities to the following colours: blue brown, pale grey, reddish-orange, wine-red or yellow. Other colours it can assume are blue, pale green, white, gold, pink (rare) reddish-yellow or opaque to transparent/translucent. Treatment of brown or pale topazes makes them bright yellow, gold, pink or violet coloured. Heat treatment and irradiation of colourless, grey or pale yellow and blue material produce darker blue. Artificially coating the mystic topaz which is colourless gives it a rainbow effect. However, exposure of some imperial topaz stones to sunlight for extended time may cause them to fade.
The application of nanogenerators and piezoelectricity in osteogenesis
Published in Science and Technology of Advanced Materials, 2019
Fu-Cheng Kao, Ping-Yeh Chiu, Tsung-Ting Tsai, Zong-Hong Lin
Piezoelectricity, also referred to as the piezoelectric effect, is the ability of certain solid materials to generate an electric field in response to mechanical deformation. It is understood that this phenomenon results from the linear electromechanical interaction between the mechanical and electrical state in crystalline materials [1]. In most crystals (such as metals), the basic repeating unit is symmetrical. However, in piezoelectric crystals, it is inversely arranged, but their electrical charges are perfectly balanced and electrically neutral. The origin of the electric field in piezoelectric material is a break in the inversion symmetry, pushing some of the atoms closer together or further apart, upsetting the balance of positive and negative forces, and causing net electrical charges to appear. This effect carries through the whole structure, so net positive and negative charges appear on the opposite, outer faces of the crystal [2](Figure 1). To better describe and discuss the piezoelectric effects of different materials, we have categorized the materials into three groups according to their nature as natural, biological, and synthetic materials. Quartz, berlinite, sucrose and topaz are examples of naturally occurring materials. Collagen of bone, silk, tooth dentin and enamel belong to biological ones. Examples of synthetic materials include barium titanate and lead zirconate titanate [3].
Cretaceous tungsten-tin mineralisation in the Tin Range, Stewart Island, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2022
Hamish C. Lilley, James M. Scott, Josh J. Schwartz, Rose E. Turnbull, Andy J. Tulloch
The upward movement of magmatically exsolved fluids occurs dominantly though fracture networks produced by the upward pneumatic/hydraulic pressure of the fluid (e.g. Sharma and Srivastava 2014). In the Tin Range, the Pegasus Group raft appears to have acted as the trap for mineralisation (Figure 7). Greisenisation is inferred to have started by the alteration of all feldspars and most of the biotite in the Tin Range Granodiorite to give the sericite-quartz matrix. Possible reactions that occurred are: Greisens enriched in W-Sn are known to have a ∼6% volume reduction as a result of the breakdown of feldspars, thereby increasing permeability (Launay et al. 2017 and generating a positive feedback loop whereby greater fluid flow enables increased greisenisation, which in turn ensues further fluid flow. The veins of Tin Range granodiorite that intruded into the Pegasus Group are the stratigraphically highest component of the Tin Range granodiorite (in the southern Tin Range) and therefore, due to increasing permeability during greisenisation, fluids trapped by the Pegasus Group raft would naturally accumulate within these veins. As a result the Tin Range granodiorite is inferred to have first been modified to a sericite-quartz mineralogy, with areas affected by greater degrees of fluid interaction evolving to quartz-topaz greisen mineralogy. Topaz in the quartz-topaz greisen has formed in the same locations as sericite in the sericite-quartz greisen; that is, surrounding quartz and as inclusions within quartz, and therefore the change in greisen type may have occurred with the alteration of the sericite directly to topaz and quartz via:
Physico-chemical Characterization of sewage sludge for thermochemical conversion processes
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020
Bijesh Raveendravarrier, Arun Palatel, Muraleedharan Chandrasekharan
The qualitative and quantitative estimation of mineral oxides in the DS and SS ash was done with the help of XRD analyzer (Make:Bruker Model D8 Advance). The DS sample was finely ground and sieved to less than 1 mm diameter powder form. This powder was heated to 1000 °C for 4 hours to obtain the SS ash. The samples for the XRD analysis were smeared over an amorphous silica holder and placed on the goniometer. The instrument was set for the 2-theta range of 80 degrees and with current and voltage set to 40 mV and 40 mA, respectively. The quantification of the mineral oxides was obtained by Rietveld method using the software Topaz 5.0.