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Related to Orthoclase: biotite, albite, microcline


KAlSi3O8 A colorless, white, cream-yellow, flesh-reddish, or gray potassium feldspar that usually contains some sodium feldspar, either as albite or analbite or in some intermediate state; it is or appears to be monoclinic. Also known as common feldspar; orthose; pegmatolite.



a rock-forming mineral of the feldspar group with the chemical composition K[AlSi3O8]. Orthoclase contains admixtures of Na (up to 8 percent Na2O); less frequently, it contains Ba and small amounts of Fe, Ca, Rb, and Cs. It crystallizes in the monoclinic system to form prismatic crystals. Twin crystals are characteristic. Orthoclase, unlike microcline, exhibits perfect cleavage at a 90° angle (hence the name “orthoclase”). It is light pink, brownish yellow, or red. The mineral has a vitreous luster, a hardness on Mohs’ scale of 6–6.5, and a density of 2,550–2,580 kg/m3.

Orthoclase is one of the principal rock-forming minerals in magmatic rocks. Clusters of large orthoclase crystals occur in pegmatite veins. The mineral is often formed during regional and contact metamorphism. Orthoclase is used in the manufacture of glassware and ceramics.

References in periodicals archive ?
The XRD results show that the albite content is higher (Figure 6(i)) (2.1%-35%) than the orthoclase content (0-4%).
XRD analysis revealed that Sevier Shale is composed of quartz, orthoclase, microcline, calcite, gypsum, chlorite, illite, and mixed layers of kaolinitemontmorillonite (Fig.
An old hoard of lawsonite specimens was released to the market in 2004, and appeared at that year's Tucson Show (see my Tucson report in May--June 2004)--but whereas the "old" Marin County lawsonite is blue-white to medium blue, the "new" Mendocino County lawsonite is brownish pink with hints of lilac, occurring as sharp, blocky crystals to 1.5 cm, resembling orthoclase or microcline.
sediments, which are low in K-bearing minerals such as mica and orthoclase, which produces illite following weathering.
Mohs Hardness Scale (the greater the number, the greater the hardness) Mohs Mineral Actual Hardness 2 Gypsum 3 3 Calcite 9 4 Fluorite 21 5 Apatite 48 6 Orthoclase Feldspar 72 7 Quartz 100 8 Topaz 200 9 Corundum 400 10 Diamond 1,600
Values in parentheses are the standard errors in the last significant figures derived from the Rietveld analysis Quartz Kaolinite Smectite Orthoclase Albite Anatase Dome saprolite at 0.25m 35 (1) 30 (2) 34 (2) <1 <1 <1 3 (1) 57 (2) 39 (2) -- -- 1 (1) Basal saprolite at 0.40m 39 (1) 25 (1) 33 (2) <1 <1 <1 4 (1) 49 (I) 47 (2) 1 (1) Sandstone 0.20m from clay root at 1.30 m 41 (2) 22 (2) 31 (2) 4 (l) 2 (1) <1 2 (1) 45 (3) 53 (3) -- -- l (1) Sandstone 0.30m from clay root at 1.30m 49 (2) 15 (2) 29 (2) 5 (1) 2 (l) <1 2 (1) 42 (3) 56 (3) -- -- l (1) Table 3.
Whereas the occurrence of larger feldspar, orthoclase and plagioclase phenocrysts are common in West Pacific volcanic glass sources (Smith 1974), none of those samples containing microphenocrysts are from the Kutao/Bao source of West New Britain.
It is a medium-grained, light grey, salt-and-pepper granodiorite, and is composed essentially of quartz, orthoclase and plagioclase feldspar, minor biotite and hornblende, and accessory magnetite.
47 What completes this list: talc, gypsum, calcite, flurorite, apatite, orthoclase feldspar, quartz, topaz, corundum...?
The feldspar fraction is dominantly altered orthoclase feldspar and perthitic ortho-clase feldspar with traces of microcline and plagioclase.