“Feldspar” is the name of a large group of rock-forming silicate minerals that make up over 50% of Earth’s crust. Feldspars have no color of their own because they lack chromofore chemical elements in their structure. Quartz is another framework silicate, consisting only of oxygen and silicon, but feldspar has various other metals partly replacing the silicon. What is common to all the feldspars is the same arrangement of atoms, a framework arrangement, and one basic chemical recipe, a silicate (silicon plus oxygen) recipe. Feldspar minerals have very similar structures, chemical compositions, and physical properties. Pegmatites are coarse, crystalline, igneous rocks that are formed during water-wet stages of magma cooling. High temperatures of formation correspond to more disordered and more symmetric feldspars. Structure and composition of feldspars. Gem quality clear feldspars, moonstone and labradorite are used in jewelry. It is generally mined from large bodies of granite, pegmatites, and sands. Feldspars belong to the tectosilicates, sometimes referred also as network silicates. In the building up of this framework, four-membered rings of tetrahedrons play an important role. The structure of the double crankshaft, and consequently mineral symmetry, is controlled by the distribution of aluminum and silicon among the tetrahedra. The structures of individual feldspar varieties are all based on this model, … Feldspars are a group of aluminosilicate minerals in which the silicon and aluminum tetrahedra share all four apical oxygen ions with neighboring tetrahedra in such a way that the structure is a three-dimensional framework (see Vol. Labradorite rich rocks or amazonite granites are also used as decorative building stones. All feldspars have low symmetry, being only monoclinic, 2/m, to triclinic, bar 1. Internal reflections from exsolution lamellae, inclusions, cleavage surfaces, etc. Feldspars are mostly used in ceramics industry. The structure of feldspars is a three-dimensional framework of oxygen tetrahedrons in which a Si or Al ion is situated. The crankshafts are joined together in an open structure with large volds to hold the alkalis or calcium (see attached draw-ing). shafts” parallel to the a-axis of the monoclinic or triclinic structure. They tend to twin easily and one crystal can even be multiply twinned on the same plane, producing parallel layers of twinned crystals. But they are almost never transparent either. [1] They are found in igneous, metamorphic, and sedimentary rocks in all parts of the world. Lower temperatures of formation cause the Al-Si distribution to be more ordered and reduce symmetry. Every oxygen is again linked to two of these Si or Al ions. The structure of feldspar is such that it can facilitate the presence of many other elements. Feldspar Formulas and Structure . make the pure feldspar white in color. The feldspars are a group of minerals that have similar characteristics due to a similar structure.