Anorthite

ppl coarse-grained laths 10*

xpl w/ CPX and OPX 10*

group                                   feldspar
system                                  triclinic
formula                                 NaAlSi3O8-CaAl2Si2O8
optic                                   biaxial pos / neg
Too-Vee                                 75 - 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, clay minerals, zeolite
habit.1                                 tabular, columnar
occurence                               igneous (mafic, ultramafic), metamorphic (carbonate), sedimentary
TwoV                                    2 3
relief                                  1 4
pleochroism.2                           
birefringence                           1 3 4 5 6 7 
cleavage.2                               {001} perfect, {010} good intersect at 94¡