The mineralogical composition of most feldspars can be expressed in terms of the ternary system Orthoclase (KAlSi3O8), Albite (NaAlSi3O8) and Anorthite (CaAl2Si2O8). Chemically, the feldspars are silicates of aluminium, containing sodium, potassium, iron, calcium, or barium or combinations of these elements.
What is the formation of feldspar?
Many feldspars are igneous as they commonly precipitate out in magma as it cools. They may also be formed as metamorphic minerals in veins of other rocks. This process involves both heat and pressure. Finally, over time feldspar can weather to produce sediments.
What is the chemical formula of amphibole?
Chemical composition
Numerous common amphiboles can be represented within the Mg7Si8O22(OH)2 (magnesio-anthophyllite)–Fe7Si8O22(OH)2 (grunerite)–“Ca7Si8O22(OH)2” (hypothetical pure calcium amphibole) compositional field (Figure 1). This diagram is commonly referred to as the amphibole quadrilateral.
Is feldspar felsic or mafic?
Felsic rocks are mostly feldspar (especially K-feldspar), at least 10% quartz, and less than 15% mafic minerals (biotite, hornblende).
What type of rock is muscovite?
Muscovite typically occurs in metamorphic rocks, particularly gneisses and schists, where it forms crystals and plates. It also occurs in granites, in fine-grained sediments, and in some highly siliceous rocks. Large crystals of muscovite are often found in veins and pegmatites.
Is feldspar a silicate or non silicate?
Silicate minerals are by far more common, making up more than 90% of the earth. These include feldspars, as well as quartz and mica. Additionally, non-silicate minerals make up the last ten percent or so. These include carbonates like limestone and marble, sulfates like gypsum, and halides like table salt.
What type of rock is plagioclase feldspar?
Plagioclase feldspar group minerals are the most common rock-forming minerals. They are importantly dominant minerals in most igneous rock. They are major constituents in a wide range of intrusive and extrusive igneous rocks including granite, diorite, gabbro, rhyolite, andesite, and basalt.
Is plagioclase feldspar a silicate?
Plagioclase is a member of the feldspar group (like orthoclase) and is a framework silicate. Plagioclase consists of a solid solution between the albite and anorthite end-members, and together with quartz is the most common of the rock forming minerals.
What is a chemical property of amphibole?
Typically, amphiboles form as long prismatic crystals, radiating sprays and fibrous aggregates. They are generally dark coloured though their colours can range from colourless to white, green, brown, black, blue or lavender. This property is related to composition, particularly iron content.
Is amphibole a sheet silicate?
5 Biotite mica (left) and muscovite mica (right). Both are sheet silicates and split easily into thin layers along planes parallel to the sheets. Biotite is dark like the other iron- and/or magnesium-bearing silicates (e.g., olivine, pyroxene, and amphibole), while muscovite is light coloured.
How is orthoclase feldspar formed?
Most orthoclase forms during the crystallization of a magma into intrusive igneous rocks such as granite, granodiorite, diorite, and syenite. Significant amounts of orthoclase are also found in extrusive igneous rocks such as rhyolite, dacite, and andesite.
