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Recognising the different types of building stone
Published in John A. Hudson†, John W. Cosgrove, Understanding Building Stones and Stone Buildings, 2019
John A. Hudson†, John W. Cosgrove
As can be seen from Figure 3.6, the textures and colours of granites are varied. Their colour is generally controlled by the colour of the feldspar, the main mineral constituent; feldspars are aluminium silicates and their colour is determined by the alkali metals they contain. Orthoclase is a pink feldspar and contains potassium; plagioclase is a white to grey feldspar and contains sodium and calcium. The Peterhead granite in Figure 3.6 is dominated by orthoclase which gives it its characteristic pink colour, and the example illustrated contains a small black inclusion of the rock into which the granite was intruded. Depending on their composition and the time they spent in the magma before it cooled and solidified, these xenoliths (literally foreign rocks) may become completely assimilated by the magma or may remain intact as in the example illustrated here.
Minerals
Published in W.S. MacKenzie, A.E. Adams, K.H. Brodie, Rocks and Minerals in Thin Section, 2017
W.S. MacKenzie, A.E. Adams, K.H. Brodie
Orthoclase is the name given to untwinned or simply twinned potassium-rich feldspar found in many granitic rocks. Since it cannot easily be distinguished from sanidine there is a tendency to restrict usage of the name orthoclase to indicate the potassium end-member of the alkali feldspar series.
Inorganic Polymers
Published in Charles E. Carraher, Carraher's Polymer Chemistry, 2017
Quartz is an important network silicate (Section 12.11). A number of additional tetrahedral silicate-like materials possess some AlO4 tetrahedra substituted for the SiO4 tetrahedra. Such structures offer a little larger “hole” in comparison to the entirely SiO4 structures, allowing the alkali and alkaline-earth cations to be introduced. Feldspar (orthoclase) is such a mineral. The alumino-silicate networks are almost as hard as quartz. For feldspar and other tetrahedral networks, the number of oxygen atoms is twice the summation of silicon and other MO4 cations.
Chemical and mineralogical investigations of lime plasters of medieval structures of Hampi, India
Published in International Journal of Architectural Heritage, 2019
Manager Singh, Selvam Vinodh Kumar, Pandurang Digamber Sabale
The acid insoluble fractions of the samples showed coarse medium-grained sand to fine-sized clay fragments. The aggregate grains were identified as potash feldspar/pink feldspar (orthoclase) to soda feldspar/grayish white plagioclase. The proportions of potash feldspar are comparatively higher to soda feldspar. The orthoclase and plagioclase feldspars show shiny sub-vitreous shape with weak planes (cleavage). The feldspar grains are intermixed with irregular-size-shaped quartz grains. The grey-colored amorphous, highly jointed, fine clay matrix partially cemented the grains. This fraction of the clay minerals also provided plasticity to the plaster. The quartz grains are easily indentified on the basis of its vitreous, transparent luster with conchoidal features. The orthoclase/plagioclase feldspar was recognized from its medium pinkish to whitish-grey-colored tabular-shaped grains. The transparent to dirty white, vitreous, massive quartz grains are in higher proportions to that of feldspar grains. Some of the quartz grains showed uneven, non-homogeneous polycrystalline nature probably due to the presence of impurity by hydro chemical reactions during their genesis. The proportions of clay size minerals are far lesser compared to other constituents. The lime binder is fine grained. The size and texture of the calcite grains formed in the plaster is probably related with the environmental condition during the period of carbonation. The aggregate grains sieved after dilute HCl digestion of the plaster is shown in Figure 3a. The typical lime plaster is shown in Figure 3b.