Staurolite

xpl 20*

ppl 20*

group                                   orthosilicate
system                                  monoclinic
formula                                 Fe2Al9O6(SiO4)4(OH)2
optic                                   biaxial pos
Too-Vee                                 80 - 90¡
relief.1                                high pos
min. index                              1.736 / 1.762
color                                   yellow, brown
pleochroism                             yes
birefringence.1                         0.009 - 0.015
cleavage                                no
elongation                              yes
extinction                              parallel, symmetrical
angle                                   0¡
alteration                              sericite, andalusite, kyanite, garnet, and cordierite
habit.1                                 prismatic, tabular, columnar
occurence                               metamorphic (medium grade, pelite), sedimentary (clastic)
TwoV                                    2
relief                                  3
pleochroism.2                           yellow, brown, red
birefringence                           1 4 5 6 7
cleavage.2                              {010} not seen in thin section