Uses of QuartzFeldspar GroupOrthoclase (Or)PlagioclaseUse Used in ceramics but less than Kspar.ZeolitesTectosilicatesThree-quarters of the rock crust of the earth is made up of tectosilicates. Remember that all the oxygens (and anions) are shared with neighboring tetrahedra.SiO2 GroupQuartz low and highTridymiteCristobaliteOpalFeldspar GroupAlkali Feldspars: Microcline, Orthoclase, and Sanidine: KAlSi3O8 (rememberthat these show order-disorder polymorphism)Orthoclase Microcline Sanidine phenocrystsAlbite NaAlSi3O8 is also an alkali feldsparPlagioclase Feldspars: Albite NaAlSi3O8 through Anorthite CaAl2Si2O8Feldspathoid GroupFeldspar-like minerals that are deficient in silica content. These are relatively rare and are important in the classification of igneous rocks. Minerals include leucite, nepheline, sodalite, and lazurite.Zeolite GroupThis group includes many different minerals that are hydrous and rich in Ca, Na, Si, and O.These minerals are particularly common in the volcanic rocks of the North Shore of Lake Superior.SiO2 GroupThese include low and high quartz (alpha and beta), cristobalite (high and low), tridymite (high and low), stishovite and coesite.Low Quartz (inverts from high quartz on lowering temperature, which may produce twinning)Hardness is 7; g = 2.65, fracture=conchoidal, luster- vitreous, lots of different colors.Occurrence:Everywhere. It is ubiquitous. It is a major constituent of granitic rocks, metamorphic rocks and of sedimentary rocks. It is not easily chemically altered. It is stable in the surface environment.Varieties include:Amethyst is purple color due to Fe+3Rose quartz Ti+4 Smokey Quartz (free Si) CitrineTiger’s-eye: yellow, fibrous quartz pseudomorphs after fibrous amphiboleMicrocrystallineFibrous: chalcedony, examples are agate and onyxGranular-flint, chert, jasperOpal: hydrous SiO2 mineral that is slightly amorphous and much less dense than quartz. It has iridescence and is used as a semi-precious gemstone.Uses of QuartzQuartz is used as a gemstone and as ornaments. It is part of sand that is used in mortar, concrete,and it is used as a flux, as an abrasive, and in the manufacture of glass/silica bricks. It is also used in lenses/prisms. Because it is piezoelectric, it is used in radio oscillators to permit both transmission and reception. It is used in pressure switches such as those in watches. (Piezoelectric: if pressure is exerted at the ends of a polar axis, a flow of electrons toward one end produces a negative electron charge on one end and a positive on the other.)Feldspar GroupKAlSi3O8------NAlSi3O8-------CaAl2Si2O8 Or Ab AnAlkali PlagioclaseIn the feldspars the distribution of Al in the tetrahedral sites can be ordered on particular sites, or can be randomly distributed within the tetrahedral sites in the feldspar structure. This is a functionof temperature and is known as the structural state. In feldspars that form at high temperature and are quenched (Kspar in lavas for example), you may have disordered Kspar (sanidine) or if you have slow cooling of the feldspars or they form at moderate to low temperatures, you will have ordering of Al on the tetrahedral sites.The alkali feldspars show complete solid solution at high temperatures. However is the feldspar isallowed to cool slowly, the Ab and Kspar components of the mineral will exsolve out from one another. When this results in lamellae of Ab in Kspar, it is called perthite. When it results in Kspar lamellae in Ab, it is called antiperthite. There is complete solid solution between albite and anorthite. There is very limited solid solution between orthoclase and anorthite.Orthoclase (Or)Or is monoclinic, commonly occurs in crystals or in coarsely cleavable (3 cleavages) to granular masses. It is most abundant in rocks as anhedral grains. Its color (pinkish-salmon), hardness (6), right-angled cleavage and its lack of striations recognize it. It is a common mineral in granite, granodiorite and syenite. It is commonly twinned; the most common of which is the Carlsbad Twin.Use Along with the Kspar minerals, it is used to make porcelain with clay and quartz.PlagioclasePlagioclase is triclinic and is nearly always twinned, with the Albite twin law. It is commonly found in crystals or in coarsely cleavable to granular masses. It has 3 cleavages at nearly right angles. Its color can vary from white (in albite) to green to gray to pink. Its luster is vitreous to pearly. It is distinguished by its striations that are caused by albite twinning.It has two compositions where it shows iridescence: from An 2-15 (peristerite-rare) and from An 47-58 (labradorite).LabradoriteAs a rock-forming mineral, plagioclase is more widely distributed than Kspar. It is found in mafic igneous rocks such as gabbro, diorite and also in felsic rocks such as granite and granodiorite. It is also common in metamorphic rocks. The classification of igneous rocks is based on the feldspar present, as well as its type and its relative amount.Plagioclase Solid SolutionAnorthite is the high temperature end member, albite the low. Albite: An 0-10, also known as alkali feldspar along with Kspar. Found in granite, syenite, rhyolite,tachyte and in pegmatites. Oligoclase: An 10-30, found in granodiorite and in monzoniteAndesine: An 30-50, found in diorite and andesite Labradorite: An 50-70, found in gabbro, basalt. A rock composed of >90% plagioclase (An 50-70) is called an anorthosite.Bytownite: An 70-90. Rarely found.Anorthite: An 90-100. Rare, found in rocks rich in mafic minerals.Use Used in ceramics but less than Kspar.ZeolitesThese are hydrous Ca and Na tectosilicates, which have Al present in both tetrahedral and octahedral sites. There are a large number of voids in their structures, up to 8 Å. The hardnesses vary from 3.5 to 5.5 and the specific gravity from 2 to 2.4. The name is derived from the fact thatwhen you fuse ground up mineral, it swells. Zeo means boil and lite means stone (from the Greek).These minerals (there are numerous species) are found in cavities and veins in mafic igneous rocks. They commonly occur as fillings of amygdules in the North Shore Volcanic Group. In the western U.S., they occur as alterations of volcanic tuff and volcanic glass. They form at low pressure and temperature. These minerals have structures that are very open with large interconnecting spaces or channels. They have habits that vary from fibrous to platy to equant.