Which set of minerals is commonly associated with sanidine in igneous rocks?

Which set of minerals is commonly associated with sanidine in igneous rocks?

• A. Quartz, Muscovite, Biotite, Plagioclase Feldspars
• B. Calcite, Gypsum, Dolomite, Halite
• C. Olivine, Pyroxene, Amphibole, Feldspar
• D. K-Feldspar, Quartz, Magnetite, Apatite

Answer: (A)

Sanidine is the high-temperature form of potassium feldspar that crystallizes in felsic, silica-rich magmas, such as rhyolites and granites. In these rocks you commonly find a quartz-rich, mica-bearing assemblage with feldspars, where quartz signals silica saturation and plagioclase coexists with alkali feldspar. Muscovite and biotite are common dark micas in such felsic systems, accompanying the K-feldspar as the rock crystallizes. This combination—quartz together with both micas and plagioclase along with sanidine—best reflects the typical igneous-rock paragenesis where sanidine occurs. The other mineral groupings lean away from this felsic, silica-rich context: carbonates and evaporites are not igneous minerals; mafic minerals like olivine, pyroxene, and amphibole with feldspar indicate a different, lower-silica rock type; while magnetite and apatite can occur in felsic rocks but do not define the same common association with sanidine as quartz, muscovite, biotite, and plagioclase do.

Sanidine is the high-temperature form of potassium feldspar that crystallizes in felsic, silica-rich magmas, such as rhyolites and granites. In these rocks you commonly find a quartz-rich, mica-bearing assemblage with feldspars, where quartz signals silica saturation and plagioclase coexists with alkali feldspar. Muscovite and biotite are common dark micas in such felsic systems, accompanying the K-feldspar as the rock crystallizes. This combination—quartz together with both micas and plagioclase along with sanidine—best reflects the typical igneous-rock paragenesis where sanidine occurs.

The other mineral groupings lean away from this felsic, silica-rich context: carbonates and evaporites are not igneous minerals; mafic minerals like olivine, pyroxene, and amphibole with feldspar indicate a different, lower-silica rock type; while magnetite and apatite can occur in felsic rocks but do not define the same common association with sanidine as quartz, muscovite, biotite, and plagioclase do.