Y.A.G. :

Yttrium Alluminium Garnet ; artificial garnet

Y₃Al₅O₁₂

Physical and optical properties :

Colours : colourless, yellow, green ( coloured by chrome ), blue, violet, red

Transparency : transparent

Hardness : 8 to 8.5

Density : 4.55 to 4.60

R.I. : 1.833

Dispersion : 0.015

System cubic

YANOLITE :

Variety of violet axinite 

YARRA YARRA :

Australian name for a cat’s eye opal 

YELLOW ASHOVER SPAR :

English Name given to a yellow fluorite 

YELLOW GROUND :

English name given to " blue ground " altered through oxidation of the iron content

YGaG :

Yttrium Gallium Garnet ;

artificial garnet of pink colour

YIG :

Yttrium Iron Garnet ;

artificial opaque garnet

Y₃Fe₂(FeO₄)₃

YOUSTONE :

Old English Term designating jade ; See YU or YU-CHI

YTTROGRANAT :

Artificial Aluminate of yttrium ; German synonym for YAG 

YU or YU-CHI :

Chinese name for jade ; Yu = ‘ beautiful stone ’