Nepheline

1. ppl nepheline x5

2. xpl nepheline x5

3. xpl nepheline x5

4. ppl plutonic nepheline x5

5. xpl plutonic nepheline 5

group                                   feldspathoid
system                                  hexagonal
formula                                 Na3K(Al4Si4O16)
optic                                   uniaxial neg
Too-Vee                                 0¡
relief.1                                low neg / pos
min. index                              1.529 / 1.544
color                                   colorless
pleochroism                             no
birefringence.1                         0.003 - 0.005
cleavage                                no
elongation                              no
extinction                              parallel
angle                                   0¡
alteration                              clay minerals, analcime, sodalite, calcite, cancrinite
habit.1                                 equant, columnar, prismatic
occurence                               igneous (alkalic), metamorphic (metasoma- tism)
TwoV                                    
relief                                  1 4
pleochroism.2                           
birefringence                           1 2
cleavage.2                              {1010), {0001}, not usually seen