One of the mysteries of the English language finally explained.
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 glass-making.
- ‘The microgranite has a felsitic groundmass containing microphenocrysts of albite and orthoclase along with phenocrysts of corroded quartz and sporadic dihedral garnet.’
- ‘Most of the intrusion comprises a coarse-grained, pink gneissic granite containing numerous augen of recrystallized perthitic orthoclase up to 1.25 cm across.’
- ‘Some larger grains also occur, and most grains are slightly perthitic showing variable degrees of transformation from orthoclase to microcline.’
- ‘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.’
- ‘Leucosomes generally plot on the high orthoclase side of the leucogranites and Grampian Granites plot on the low side.’
- ‘Of these, alkali feldspar, particularly orthoclase, is the most common.’
- ‘The mineral occurs with smoky quartz, aegirine, and orthoclase.’
- ‘He further stated that the lithophysae are lined with orthoclase and quartz, and the cavities are partially filled with calcite, quartz, and chlorite.’
- ‘Calcic amphiboles, including hornblende and actinolite are abundant, and probably are alteration products, which also include albite, orthoclase and rare pyrite.’
- ‘The central potassic zone is characterized by the presence of potassium-bearing minerals such as orthoclase (a potassium feldspar) and biotite.’
- ‘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.’
- ‘A slightly bluish-gray feldspar, probably either microcline or orthoclase, without polysynthetic twinning lines occurs as crystals to 2 cm across.’
- ‘Associated minerals are white orthoclase, milky quartz, and muscovite.’
- ‘Quartz, microcline or orthoclase and plagioclase are ubiquitous in the Everest granites, which also contain varying amounts of tourmaline, muscovite, biotite and garnet.’
- ‘Examples of silicates include quartz, orthoclase, and olivine.’
- ‘He mentions that the amazonite occurred in association with orthoclase (almost certainly microcline), smoky quartz, specular hematite, and rare anhydrite.’
- ‘Two-feldspar thermometry fails to retrieve peak temperatures from these rocks owing to late stage unmixing reducing the albite content of orthoclase.’
- ‘Orthoclase is a polymorph of other minerals that share the same chemistry, but have different crystal structures.’
- ‘Feldspars are added as orthoclase in order to reduce the devitrification of the glass.’
- ‘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.’
Mid 19th century: from ortho- ‘straight’ + Greek klasis ‘breaking’ (because of the characteristic two cleavages at right angles).
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