Talc

xpl 20*

ppl 20*

xpl 20*

ppl 10*

xpl 10*

ppl 20*

group                                   phyllosilicate
system                                  triclinic
formula                                 Mg3Si4O10(OH)2
optic                                   biaxial neg
Too-Vee                                 0 - 30¡
relief.1                                low to mod pos
min. index                              1.538 / 1.602
color                                   colorless
pleochroism                             no
birefringence.1                         0.030 - 0.050
cleavage                                yes
elongation                              yes
extinction                              parallel
angle                                   0¡
alteration                              chlorite
habit.1                                 fibrous, tabular, acicular
occurence                               metamorphic (carbonate), hydrothermal
TwoV                                    1 
relief                                  1 2
pleochroism.2                           
birefringence                           9 11 12 13
cleavage.2                              {001} perfect