Sanidine In Thin Section

At 10x magnification the sanidine is too large for a complete view of the crystal but the fine matrix surrounding it allows clear distinction of its boundaries and shape.

Sanidine in thin section. Sanidine is an alkali feldspar intermediate in composition between albite and orthoclase. Crystals commonly tabular on f010g with a square cross section to 50 cm. Click on image to view the slight zoning visible on the underside of the crystal.

Quartz has similiar appearance but is uniaxial and has positive relief. In thin section sanidine lacks polysynthetic twinning compared to mirocline and plagioclase. Can distinguish low and high sanidine and orthoclase by the 2v value.

In thin section alkali feldspar grains often look like they re sprinkled with dirt ppl or tiny confetti xpl. Sanidine k na al si 4o8 c 20 1m i nera ld t pub sh g v o. Thin section of twinned sanidine crystal in crossed polarized light.

Sanidine crystals are commonly euhedral in phenocrysts either essentially square in section or elongated parallel to a axis. Only carlsbad twinning is common in sanidine bisecting phenocrysts or microlites parallel to either length. Carlsbad twins are common baveno and manebach twins rarer.