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Luster/Transparency : pearly, vitreous/translucent. good cleavage on {010}. Pure orthoclase is rare some sodium is usually present in the structure. Polymorphism Orthoclase crystals and twins provide information on the formation of minerals and environmental factors. Because of this the alkali feldspars exist in a range of chemical compositions between pure albite (NaAlSi3O8) and pure orthoclase (KAlSi3O8). As light penetrates a moonstone cabochon, some of that light scatters at the boundaries between the two interlayered feldspar materials. From Guanajuato, Mexico. The scattered light illuminates the stone and produces a phenomenal glow that appears to move beneath the cabochon’s surface. The glow is usually white in color and is the source of the “moonstone” name. All feldspar minerals are usually translucent to transparent, display two directions of cleavage that intersect at approximately 90 degrees, have a vitreous to pearly luster on cleavage faces, and have a specific gravity between about 2.5 and 2.6. cleavage angle. In California, from the Pala and Mesa Grande districts, San Diego Occurrence. Associated Minerals include (??). Pennsylvania. History. It can be difficult to Widespread. Specific Gravity : 2.55-2.63 Enhancements ... Orthoclase is from Greek words meaning break straight because the cleavages are at 90°. Pink Granite: A specimen of coarse-grained granite with pink crystals of orthoclase. Excellent crystals associated with Aegirine come from Mount Malosa, Malawi. Betroka, Madagascar. Orthoclase has several commercial uses. Gem crystals from Ampandrandava, Fianarantsoa, and Itrongay, near These gems commonly range from colorless to a bright yellow color. It will develop abrasions if used in most types of jewelry, and it can easily cleave upon impact. Specific gravity is the density of a material, in this case a mineral, compared to an equivalent volume of water. Mineral Group: Feldspar (alkali) group; (Al,Si) commonly only partially ordered. At Tanokamiyama, Shiga Prefecture, The common feldspar of granites, granite pegmatites, and syenites. CLASSIFICATION: Dana System # 76.1.1.1. It is one of the most abundant rock-forming minerals of the continental crust. If the specimen is a well-formed crystal, it will likely have a much higher value if sold as a mineral specimen than as a cutting rough. During physical weathering, grains of orthoclase are incorporated into sediments and sedimentary rocks such as sandstone, conglomerate, and siltstone. Trentino-Alto Adige, and at San Piero in Campo, Elba, Italy. The glow appears to move as the light source is moved, or as the stone is moved, or as the observer chances his angle of observation. Specific gravity: 2.56 Index of refraction: 1.52 Birefringence: weak maximum birefringence of 0.005 Pleochroism: colorless in section ... Orthoclase (KAlSi 3 O 8) is the medium temperature pure potassium end member of the alkali feldspar group. 2KAISi3O8 + 2H+ + 9H2O → H4Al2Si2O9 + 4H4SiO4 + 2K+(orthoclase + water → kaolinite + silicic acid + potassium). series with celsian. In actuality, the density of a mineral varies widely, even within a single crystal, due to the presence of impu­ rities, cracks, and bubbles. Orthoclase is a feldspar mineral with a chemical composition of KAlSi3O8. Orthoclase has a Mohs hardness of 6.0, good right-angle cleavage in two directions, and a specific gravity of 2.5-2.6. In these conditions there is the presence of a large stability field of leucite. If you hold two objects of equal volume (size), the one with more density will feel heavier. Common as Carlsbad, Baveno and From Baveno, Piedmont, in the P¯tschtal, Specific Gravity is approximately 2.59 g/cm Streak is (??). Density, or specific gravity, is a bulk property of a mate­ rial that is independent of direction and is uniform within a mass of material under ideal circumstances. Co.; in Colorado, on Mt. This is known as perthitic texture. Other worldwide sources of large Microcline crystals are the Erongo Mountains, Namibia; Papachacra, Catamarca, Argentina; the Shigar Valley, Skardu, Pakistan. There is also a labradorite moonstone, which is found only in Madagascar. Amazonite specific gravity: 2.56-2.57 Index of refraction: 1.53 Birefringence: weak maximum birefringence of 0.008 seen on {001 ... (amazonite, microcline or orthoclase) separate forming lattice type exsolution intergrowths, usually as thin layers of albite roughly parallel to {100} in a host crystal of potassium feldspar. Large crystals of orthoclase are found in igneous rocks known as pegmatite. Feldspar Mineral Classification: This ternary diagram shows how feldspar minerals are classified on the basis of their chemical composition. It is also cut as a gemstone. Orthoclase. Orthoclase is a member of the alkali feldspar series. As a mineral with a Mohs hardness of 6 and two directions of perfect cleavage, orthoclase is not an especially durable gemstone. The common feldspar of granites, granite pegmatites, and syenites. Clark Co., Nevada. yellow, white, pink. Albite, muscovite, biotite, hornblende,” schorl, beryl. A crystal like this would have a much higher price if sold as a mineral specimen than as a piece of facet rough. Moonstone is the most famous orthoclase gem. It is a major component of granite its pink crystals give granite its typical color. Orthoclase appears as well-formed, short, prismatic crystals, which are frequently twinned. Because of these similarities, the feldspar minerals can be challenging to identify with absolute confidence in the field or the introductory classroom. Orthoclase got its name because it has two directions of cleavage, which are at right angles to one another. The birefringence is .008 – .010 and the specific gravity is 2.70. The gemological name used for this phenomenon is “adularescence,” which is derived from “adularia,” an old European name for moonstone. Orthoclase is in the position of extreme potassium content. Another property that is sometimes used to distinguish between alkali and plagioclase feldspars is their different specific gravity values. In Russia, from the Mursinka-Alabashka area, near Yekaterinburg Crystalline orthoclase can also be white, colorless, cream, pale yellow, or brownish red. Adularia is also a locality-derived name from Adular-Bergstock, Switzerland, where the variety occurs. At Epprechtstein, the specific gravity of feldspar (otherwise known as Orthoclase) is 2.55-2.76. Colored Moonstone: Moonstone cabochons in a variety of colors. 2.55 – 2.63 g/cm3 (Measured)    2.563 g/cm3 (Calculated). Conclusion Testing for specific gravity with this method is fast, easy, and accurate. Cite this article as: Geology Science. This specimen is approximately two inches across. Widely distributed as a prominent rock constituent, occurring in all types of rocks; igneous, in granites, syenites, porphyries, etc. As an alkali feldspar and common rock-forming mineral, orthoclase is an essential component of all granitic rocks and many volcanic and metamorphic rocks. At the time of crystallization, these ions can substitute freely for one another in the mineral’s crystal structure. If a piece of galena has a specific gravity of 7.58, that means that it is 7.58 times heavier than a volume of water identical to the volume of that particular piece of galena. Orthoclase is most widely known as the pink feldspar found in many granites and as the mineral assigned a hardness of "6" in the Mohs hardness scale. Twin crystals are not uncommon. Pure albite has a specific gravity of about 2.62. Adularia and orthoclase are similar, but adularia is pseudo-orthorhombic. In cavities in basalts; in high-grade metamorphic rocks and as a result of potassic hydrothermal alteration; also authigenic and detrital. These feldspar minerals form a solid solution series between NaAlSi3O8 and KAlSi3O8. Occurrence, Localities and Origins: Orthoclase is one of the most common of minerals. It has also been detected in the igneous rocks of Mars during analyses done by NASA’s rovers. It has an RI of 1.550 – 1.553, which is lower than other labradorites, but higher than orthoclase moonstones. It is a raw material used in the production of glass, ceramic tile, porcelain, dinnerware, bathroom fixtures, and other ceramics. Orthoclase is found in silica-rich igneous rocks such as granite, and in high grade metamorphic rocks. The sense of Haüy's name was that the mineral was a feldspar, but he did not specify a type-locality, nor did Haüy give a chemical analysis. They are normally no more than a few inches in length, but the largest reported orthoclase crystal was over 30 feet in length and weighed about 100 tons. Crystal System: Monoclinic. Orthoclase feldspars Orthoclase (KAlSi 3 O 8) is named based on the Greek for "straight fracture," because its two cleavages are at right angles to each other. Specific Gravity (Density) : 2.55 – 2.63 (g/cm3) Refractive Index : 1.518 – 1.525 Biaxial ( – ) Orthoclase is a member of the Potassium Feldspars of the Feldspar Group of minerals that also includes Albite, Amazonite, Andesine, Anorthite, Bytownite, Hyalophane, Labradorite, Moonstone, Oligoclase, Orthoclase, Sanidine and Sunstone. Specific Gravity2.56. Streak : white. Chemical weathering alters orthoclase into clay minerals such as kaolinite in reactions similar to the one shown below. The orthoclase in these metamorphic rocks is inherited from their igneous protoliths. Well shaped crystals and twins are highly sought after by mineral collectors, and the Moonstone variety is used as a gemstone. It has a hardness of 6, a specific gravity of 2.56-2.58, and a vitreous to pearly lustre. It is used as an abrasive in scouring powders and polishing compounds. Orthoclase mineral is important for industrial uses. Japan. It is measured as the ratio of the density of the gemstone to the density of water. Optical Properties : In thin section, orthoclase has low birefringence, moderate relief, and resemblance to quartz. Member of: Feldspar Group. It can be colored white, gray, yellow or red; rarely green. For additional information, see the gemstone section on Orthoclase and Moonstone. Origin: Named in 1823 from the Greek orthos, right, and kalo, I cleave, in allusion to the mineral’s perpendicular cleavages. Specific density (also called specific gravity) Density is the mass of an object divided by its volume. Orthoclase, also known as alkali feldspar or K-feldspar, is one end-member of a solid solution between orthoclase and albite. specific gravity, Absolute or true specific gravity, Table of specific gravity of soil constituent \[G = \frac{\gamma_{s}}{\gamma_{w}}\] The Indian Standard specifies 27°C as the standard temperature for reporting the specific gravity. The alkali feldspars include albite (NaAlSi3O8), anorthoclase ((Na,K)AlSi3O8), sanidine ((K,Na)AlSi3O8), orthoclase (KAlSi3O8), and microcline (KAlSi3O8). It can be difficult to see cleavage in thin section due to orthoclase s low relief. 5. 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