Feldspar
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Feldspar is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the
Specimen of rare plumbian (lead-rich) feldspar
Crystallized white feldspar, with an upright 4 cm aquamarine crystal perched on it
Feldspar and moonstone, from Sonora, Mexico
A cluster of euhedral feldspar crystals with a schorl crystal
Granite
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Granite is a coarse-grained intrusive igneous rock composed mostly of quartz, alkali feldspar, mica and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slow
Feldspar
…of contrasting alkali feldspar compositions during cooling of an intermediate composition. The perthitic textures in the alkali feldspars of many granites can be seen with the naked eye. Microperthitic textures in crystals are visible using a light microscope, whereas cryptoperthitic textures can be seen…
Granite containing plagioclase feldspar, potassium feldspar, quartz, biotite, and/or amphibole
Granite with a moderate amount of plagioclase, alkali feldspar, and quartz
Granite with a composition of alkali feldspar and quartz
Granite in thin section, under cross-polarized light