| The central potassic zone is characterized by the presence of potassium-bearing minerals such as orthoclase and biotite. |
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| Leucosomes generally plot on the high orthoclase side of the leucogranites and Grampian Granites plot on the low side. |
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| Feldspars are added as orthoclase in order to reduce the devitrification of the glass. |
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| Some larger grains also occur, and most grains are slightly perthitic showing variable degrees of transformation from orthoclase to microcline. |
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| He mentions that the amazonite occurred in association with orthoclase, smoky quartz, specular hematite, and rare anhydrite. |
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| In the vein's central vug, ferroaxinite overlies a selvage of quartz, orthoclase, and microcline feldspar and is followed by fine-grained calcite. |
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| Moonstone is the most well known potassium feldspar of the orthoclase species. |
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| A combination of orthoclase and albite arranged in layers cause the lovely sheen. |
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| A slightly bluish-gray feldspar, probably either microcline or orthoclase, without polysynthetic twinning lines occurs as crystals to 2 cm across. |
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| Calcic amphiboles, including hornblende and actinolite are abundant, and probably are alteration products, which also include albite, orthoclase and rare pyrite. |
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| Technically, moonstone belongs to the orthoclase branch of the feldspar family and rainbow moonstone is in the labradorite branch. |
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| The microgranite has a felsitic groundmass containing microphenocrysts of albite and orthoclase along with phenocrysts of corroded quartz and sporadic dihedral garnet. |
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| Spherulites frequently have a radiating structure that results from an intergrowth of quartz and orthoclase. |
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| Associated minerals are white orthoclase, milky quartz, and muscovite. |
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| Quartz, microcline or orthoclase and plagioclase are ubiquitous in the Everest granites, which also contain varying amounts of tourmaline, muscovite, biotite and garnet. |
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| Of these, alkali feldspar, particularly orthoclase, is the most common. |
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| Two-feldspar thermometry fails to retrieve peak temperatures from these rocks owing to late stage unmixing reducing the albite content of orthoclase. |
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| Most of the intrusion comprises a coarse-grained, pink gneissic granite containing numerous augen of recrystallized perthitic orthoclase up to 1.25 cm across. |
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| He further stated that the lithophysae are lined with orthoclase and quartz, and the cavities are partially filled with calcite, quartz, and chlorite. |
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| Examples of silicates include quartz, orthoclase, and olivine. |
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| The main minerals in the sample are quartz, perthitic orthoclase, plagioclase with sericite, epidote and chlorite. |
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| They are found in alkalic rocks such as nepheline syenites and phonolites, wherein they are associated with orthoclase, feldspathoids, augite, and sodium-rich amphiboles. |
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| The following major and minor minerals were identified in the samples examined: quartz, orthoclase, albite, anorthite, biotite, muscovite, garnet, secondary chlorite, kaolinite, magnetite, ilmenite, hematite, and apatite. |
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| Because the intermediate members, called orthoclase microperthites, cannot blend homogeneously, they take the form of intergrowths of microscopic but distinct crystals of the sodium and potassium end-members. |
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| In the Earth's crust the alkali feldspars display a range of ordering from the fully random distribution of sanidine and orthoclase to the fully ordered distribution of microcline. |
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| Andesite or diorite minerals, such as andesine with either pyroxene or amphibole, crystallize next and are followed by orthoclase and quartz, which are the essential constituents of rhyolite or granite. |
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| For example, orthoclase is typically feldspar from granite, while its modifications occur in lavas of similar composition. |
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| The feldspar fraction is dominantly altered orthoclase feldspar and perthitic ortho-clase feldspar with traces of microcline and plagioclase. |
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| These are two types of feldspars of which plagioclase feldspars are more abundant than K-feldspars like orthoclase and microcline. |
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| Orthoclase is a polymorph of other minerals that share the same chemistry, but have different crystal structures. |
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| Orthoclase occurred as remnant phenocrysts in a groundmass of chloritic material resulting from alteration of iron-rich felsite cobbles. |
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