Fayalite

1. ppl fayalite x10

2. xpl fayalite x10

group                                   olivine
system                                  orthorhombic
formula                                 (Fa,Fe2SiO4)
optic                                   biaxial neg
Too-Vee                                 46 - 98¡
relief.1                                high pos
min. index                              1.636 / 1.879
color                                   colorless, yellow
pleochroism                             yes
birefringence.1                         0.033 - 0.052
cleavage                                no (
elongation                              no
extinction                              parallel
angle                                   ***
alteration                              iddingsite, chlorophaeite
habit.1                                 equant,  granular
occurence                               igneous (mafic), metamorphic (carbonate)
TwoV                                    2 3
relief                                  3
pleochroism.2                           yellow, orange, brown
birefringence                           9 12 13
cleavage.2                              ( {010}, {110} not seen in thin section )