group feldspar
system monoclinic
formula (K,Na)AlSi3O8
optic biaxial neg
Too-Vee 40 - 70¡
relief.1 low neg
min. index 1.514 / 1.533
color colorless (cloudy)
pleochroism no
birefringence.1 0.005 -0.008
cleavage yes
elongation no
extinction inclined, parallel
angle 0 - 13¡
alteration clay minerals, sericite
habit.1 equant, tabular
occurence igneous (felsic), metamorphic (contact, regional)
TwoV
relief
pleochroism.2
birefringence
cleavage.2 {001} perfect, {010} good intersect at 90¡