Home PageAbout MindatThe Mindat ManualHistory of MindatCopyright StatusWho We AreContact UsAdvertise on Mindat
Donate to MindatCorporate SponsorshipSponsor a PageSponsored PagesMindat AdvertisersAdvertise on Mindat
Learning CenterWhat is a mineral?The most common minerals on earthInformation for EducatorsMindat ArticlesThe ElementsThe Rock H. Currier Digital LibraryGeologic Time
Minerals by PropertiesMinerals by ChemistryAdvanced Locality SearchRandom MineralRandom LocalitySearch by minIDLocalities Near MeSearch ArticlesSearch GlossaryMore Search Options
The Mindat ManualAdd a New PhotoRate PhotosLocality Edit ReportCoordinate Completion ReportAdd Glossary Item
Mining CompaniesStatisticsUsersMineral MuseumsClubs & OrganizationsMineral Shows & EventsThe Mindat DirectoryDevice SettingsThe Mineral QuizTime Machine
Photo SearchPhoto GalleriesSearch by ColorNew Photos TodayNew Photos YesterdayMembers' Photo GalleriesPast Photo of the Day GalleryPhotography
Polymorph of:
Feldspar Group.K Feldspar subgroup.Celsian-Orthoclase Series.
An intermediate, partially ordered member of theK-feldspar structural series, between disordered, monoclinicsanidine and completely orderedmicrocline. Because of its intermediate nature, it’s species status could be questioned, but it has grandfather status.
Although petrologists have long used microscopic twinning and other optical properties as a method of distinguishing orthoclase from microcline and sanidine, Wright and Stewart (1958) used the position of certain d values inXRD patterns to calculate the degree of disorder of a K-feldspar (plus it’s Na content) and thus have a more quantitative method to identify its structural state.
Sanidine forms in rapidly cooled volcanic rocks (eg.Rhyolite) and some high level intrusive dykes, whilst microcline forms in more slowly cooled rocks like granite pegmatites. Orthoclase is the most common member of the series, being the dominant K-feldspar in mostgranite, granitic rocks and other plutonic rocks, with an intermediate cooling regime. Despite the enormous number of reports of orthoclase ingranite pegmatites, orthoclase is rare in pegmatitic pockets. It has, however, been known to be stabilised by structural defects in some pegmatites (eg. Liu et al., 2018). Partially ordered, monoclinic orthoclase may persist metastably at lower temperatures (Prince et al., 1973). It constitutes some hydrothermal “adularia” (some is microcline).
Visit gemdat.org forgemological information about Orthoclase.
An intermediate, partially ordered member of theK-feldspar structural series, between disordered, monoclinicsanidine and completely orderedmicrocline. Because of its intermediate nature, it’s species status could be questioned, but it has grandfather status.
Although petrologists have long used microscopic twinning and other optical properties as a method of distinguishing orthoclase from microcline and sanidine, Wright and Stewart (1958) used the position of certain d values inXRD patterns to calculate the degree of disorder of a K-feldspar (plus it’s Na content) and thus have a more quantitative method to identify its structural state.
Sanidine forms in rapidly cooled volcanic rocks (eg.Rhyolite) and some high level intrusive dykes, whilst microcline forms in more slowly cooled rocks like granite pegmatites. Orthoclase is the most common member of the series, being the dominant K-feldspar in mostgranite, granitic rocks and other plutonic rocks, with an intermediate cooling regime. Despite the enormous number of reports of orthoclase ingranite pegmatites, orthoclase is rare in pegmatitic pockets. It has, however, been known to be stabilised by structural defects in some pegmatites (eg. Liu et al., 2018). Partially ordered, monoclinic orthoclase may persist metastably at lower temperatures (Prince et al., 1973). It constitutes some hydrothermal “adularia” (some is microcline).
Visit gemdat.org forgemological information about Orthoclase.
