Biaxial - 3 Refractive Indices - Trichroic...........

[Gem 14]

I am a bit confused about something..........

CUBIC System is ISOTROPIC with 1 Refractive index

TRIGONAL
TETRAGONAL
HEXAGONAL are all ANISOTROPIC with 2 Refractive indices

ORTHOHOMBIC
MONOCLINIC
TRICLINIC are all ANISOTROPIC with 3 Refractive indices

On the refractometer:

Cubic & amorphous gems show 1 shadow edge
Trigonal, Tetragonal & Hexagonal gems show 2 shadow edges

In the case of Ortohombic, Monoclinic & Triclinic gems are we able to see all 3 refractive indices?

Can we see them only if the stone is turned?
Can we see three shadow edges at all?

[Barbra Voltaire, FGG]

I moved your post to a more appropriate place.
Perhaps reading through this Gemology Project article might be useful.
http://www.gemologyproject.com/wiki/ind ... ractometer