A common rock-forming mineral occurring typically as white or pink crystals. It is a potassium-rich alkali feldspar and is used in ceramics and glassmaking.
‘Feldspars are added as orthoclase in order to reduce the devitrification of the glass.’
‘Of these, alkali feldspar, particularly orthoclase, is the most common.’
‘Associated minerals are white orthoclase, milky quartz, and muscovite.’
‘Leucosomes generally plot on the high orthoclase side of the leucogranites and Grampian Granites plot on the low side.’
‘The mineral occurs with smoky quartz, aegirine, and orthoclase.’
‘Examples of silicates include quartz, orthoclase, and olivine.’
‘Some larger grains also occur, and most grains are slightly perthitic showing variable degrees of transformation from orthoclase to microcline.’
‘He further stated that the lithophysae are lined with orthoclase and quartz, and the cavities are partially filled with calcite, quartz, and chlorite.’
‘Two-feldspar thermometry fails to retrieve peak temperatures from these rocks owing to late stage unmixing reducing the albite content of orthoclase.’
‘Another example is Moonstone - a variety of orthoclase mineral that, when polished, has chatoyant optical property that allows light to show as a crescent in the stone.’
‘The central potassic zone is characterized by the presence of potassium-bearing minerals such as orthoclase (a potassium feldspar) and biotite.’
‘Calcic amphiboles, including hornblende and actinolite are abundant, and probably are alteration products, which also include albite, orthoclase and rare pyrite.’
‘Quartz, microcline or orthoclase and plagioclase are ubiquitous in the Everest granites, which also contain varying amounts of tourmaline, muscovite, biotite and garnet.’
‘He mentions that the amazonite occurred in association with orthoclase (almost certainly microcline), smoky quartz, specular hematite, and rare anhydrite.’
‘In the vein's central vug, ferroaxinite overlies a selvage (fault gouge) of quartz, orthoclase, and microcline feldspar and is followed by fine-grained calcite.’
‘A slightly bluish-gray feldspar, probably either microcline or orthoclase, without polysynthetic twinning lines occurs as crystals to 2 cm across.’
‘The microgranite has a felsitic groundmass containing microphenocrysts of albite and orthoclase along with phenocrysts of corroded quartz and sporadic dihedral garnet.’
‘Amazonite crystals sometimes have white to buff-colored overgrowths of intermediate microcline, sanidine, and/or orthoclase preferentially coating the basal pinacoid and/or various prism faces.’
‘Most of the intrusion comprises a coarse-grained, pink gneissic granite containing numerous augen of recrystallized perthitic orthoclase up to 1.25 cm across.’
‘Orthoclase is a polymorph of other minerals that share the same chemistry, but have different crystal structures.’
Origin
Mid 19th century from ortho-‘straight’ + Greek klasis ‘breaking’ (because of the characteristic two cleavages at right angles).
Are You Learning English? Here Are Our Top English Tips