Page 234 - A Practical Introduction to Optical Mineralogy

Appendix B 2V size and sign of
2V, 2V.
biaxial minerals
0 20 40 60 80 90 80 60 40 20 0
humite group
norbergite -
chondrodite I-t-
Positive (2V~) Negative (2V,) humite -r-
clinohumite
Silicates 0 20 40 60 80 90 80 60 40 20 0
mica group
amphiboles phlogopite -
anthophyllite-gedrite biotite -t--
tremolite-ferroactinolite - 1-- muscovite - r-
lepidolite
the hornblende series
g laucophane paragonite
glaucophane-riebeckite r iebecki te glauconite
richterite - olivine group F< Fa r--
katophorite 1--
oxyhornblende pumpellyite
kaersutite r---
1-- pyroxene group
En Fs
eckermannite enstatite-orthoferrosilite
arfvedsonite diopside-hedenbergite -
Al 2 Si0 5 polymorphs augite
pigeonite
andalusite 1-
.
kyanite aegirine f---
sillimanite - aegirine- augite
jadeite
chlorite - I
spodumene
chloritoid - r- r- I
wollastonite
clay minerals r-- I
kaolin - ~ serpentine r-- antigorite
illite -- silica group
--- --
montmorillonite tridymite
cordierite sphene --
epidote group
zoisite
clinozoisite
epidote r---1--
feldspar group
K feldspar
plagioclase feldspar