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Minerals and rocks
Published in A.C. McLean, C. D. Gribble, Geology for Civil Engineers, 2017
Pyroxene (X2Y206), where X may be calcium, iron or magnesium, and Y is silicon or aluminium, exists in many varieties, but the most important one in igneous rocks is the mineral augite, the properties of which are listed in Table 2.6. The atomic structure of augite consists of single chains of tetrahedra [Si03]n linked laterally by calcium (Ca), magnesium (Mg) and iron (Fe) cations. The bonds between individual chains are relatively weak and the cleavage directions are parallel to the chains. Augite has two cleavages parallel to the length of the mineral, which are seen to intersect at about 90° on the basal face of its crystal (Figs 2.3, 4 & 5). Augite is common in igneous rocks which have a relatively low percentage of silica, and frequently occurs with olivine. No hydroxyl group (OH) is present in either augite or olivine and both can be described as ‘dry’ minerals. These minerals are rarely found in sediments since they alter easily when exposed to water and air (Section 2.1.5). They may be present in some metamorphic rocks.
Minerals
Published in F.G.H. Blyth, M. H. de Freitas, A Geology for Engineers, 2017
F.G.H. Blyth, M. H. de Freitas
Augite occurs chiefly in basic and ultrabasic rocks; e.g. in gabbro, where it appears as dark areas intermingled with the paler feldspar. In fine-grained basic rocks it is not distinguishable in the hand specimen unless it is porphyritic. Augite is also a constituent of some andesites and diorites, and occasionally of granites.
Characterization of scoria rock from Arabian lava fields as natural pozzolan for use in concrete
Published in European Journal of Environmental and Civil Engineering, 2022
Galal Fares, Abdulrahman Alhozaimy, Abdulaziz Al-Negheimish, Omer Abdalla Alawad
Mineralogical analysis of SR samples is shown in Figure 10. The results of XRD analysis reveal a significant amount of an amorphous glass phase presents in all SR samples. The presence of different mineralogical compositions was inferred from XRD analysis as well. The glassy phase seems to be higher in the samples collected from R3 region due to the higher halo of pozzolanicity, as demonstrated in Figures 10 and 11. Interpreted XRD patterns of the typical main peaks of two SR samples (R2S1 and R3S4) are illustrated in Figure 11. The analysis shows that SR samples contain pyroxene (augite, diopside and enstatite), olivine (frosterite) and feldspars plagioclase (albite and anorthite) minerals. Accordingly, anorthite (Ca-Al silicate), albite (Na-Al silicate), enstatite (Mg silicate), augite (Ca-Fe-Mg silicate), diopside (Ca-Mg-Fe silicates), frosterite (Mg-Fe silicates) and quartz are the main minerals whose primary peaks vary notably in SR samples from regions R1 and R2. Therefore, it is expected that the nature of these minerals might affect the pozzolanic activity of SR samples. On the other hand, augite and diopside (CA-Fe-Mg and Ca-Mg-Fe silicates, respectively) are mostly found in region R3 samples.
The role of SiO2 and silica-rich amorphous materials in understanding the origin of uncommon archeological finds
Published in Materials and Manufacturing Processes, 2020
Purification slag (Fig. 6e) forms in the reheating pit in an oxidizing atmosphere at the 1100–900°C range, during compressive hammering when slag-depleted iron bars are produced. The microstructure resembles that of furnace slag, because it actually originates from the smelting process, but often has more significant wüstite with fayalite.[16] Forge slags result from the last step of the ironworking process, with a wide variety of microstructure. This kind of slag (Fig. 6f) often contains crystalline phases with a high volume of calcium and silica. During forging sand was often used as a flux. A layered structure can often be observed, when examining purification and forge slags (Fig. 6e,f). Silicates of Fe, Ca, and Mg with Al indicate the temperature ranges of cooling and solidification of slags. Diopside and augite may form solid-solutions. Leucite is most frequently observed, while Ca-Mg silicate materials are variable. Monticellite may also indicate a temperature of ~1000°C. These temperatures fit with the metallurgical temperatures of bloomery (1200-1350°C) and the usual few hundred degrees lower forging temperatures.
Ironworking slags from Late Iron Age sites in Hungary - composition, microstructure and function
Published in Materials and Manufacturing Processes, 2020
Silicates of Fe, Ca and Mg with Al are also usually components of slags, and indicate the temperatures ranges of cooling and solidification. Diopside and augite may form solid-solutions, and lead to the interpretation of Al-containing diopside in the evaluation of XRD results. Leucite is most frequently observed, while Ca-Mg silicate materials are variable. Crystalline fayalite containing Mg could indicate that the materials formed at the highest temperature (~1200°C), while augite and diopside indicate temperatures around ~900°C. Monticellite may also indicate ~1000°C temperature. These temperatures fit with the metallurgical temperatures of bloomery (1200–1350°C) and the conventional few hundred degrees lower forging temperatures, (750–1100°C)[24] and (750–900°C).[25] Fayalite (2FeO·SiO2) is the most typical crystalline phase of bloomery slag,[26,27] and its major part is in X-ray-amorphous phase, i.e. simple iron-silicate.