Albite

1. xpl anorthitic; unzoned x10

2. xpl anorthitic; unzoned x10

group                                   tectosilicate
system                                  triclinic
formula                                 NaAlSi3O8-Ca Al2Si2O8
optic                                   biaxial pos / neg
Too-Vee                                 45 - 102¡
relief.1                                low pos / neg
min. index                              1.527 / 1.590
color                                   colorless
pleochroism                             no
birefringence.1                         0.007 - 0.013
cleavage                                yes {
elongation                              no
extinction                              inclined
angle                                   ***
alteration                              sericite (fine-grained white mica), clay, or zeolite
habit.1                                 tabular, columnar
occurence                               igneous (granitic, felsic), hydrothermal (pegmatites), metamorphic (low grade)
TwoV                                    1 2 3
relief                                  1 4
pleochroism.2                           
birefringence                           1 3 4 5 6 7
cleavage.2                              {001} perfect, {010} good, {110} poor