Phlogopite

1. ppl phlogopite E-W x5

2. ppl phlogopite N-S x5

3. xpl maximum birefringence x5

4. xpl extinction position x5

5. ppl phlogopite E-W x5

6. ppl phlogopite N-S x5

7. xpl maximum birefringence x5

8. xpl phlogopite extinction x5

group                                   mica
system                                  monoclinic
formula                                 K(Mg,Fe)3(AlSI3O10)(OH,F)2
optic                                   biaxial neg
Too-Vee                                 0 - 15¡
relief.1                                mod pos
min. index                              1.530 / 1.640
color                                   colorless
pleochroism                             yes
birefringence.1                         0.030 - 0.050
cleavage                                yes
elongation                              yes
extinction                              parallel, inclined
angle                                   0 - 9¡
alteration                              chlorite, clay minerals, sericite, Fe-Ti oxides
habit.1                                 tabular
occurence                               igneous (granitic, alkalic, felsic), metamorphic (contact, carbonate)
TwoV                                    1
relief                                  2
pleochroism.2                           brown
birefringence                           9 11 12 13 
cleavage.2                              {001} perfect