In minecraft they were origianally going to add rubeys not emeralds if i heard the story correctly.I think it would be a great addition to the game since I personally think there isn't enogh ores in minecraft considering how many ores MANY mods add I think Mojang could manage to atleast add rubys. It could work just like normal ores (gold,diamond,iron) for axample

x=ruby l=stick

x x x

x l = Ruby Axe

l

also since iron makes compass and gold makes clock...

ruby makes ore detector v=redstone

x

x v x

x

lights up within 10 blocks of ores

coal=black

iron=white

redstone=red

gold=yellow

diamond=blue

lapis=dark blue

emerald=green

basicly what you would expect

Rubys would be as rare as diamond in extreame hills biome.

So the tools would be as good as diamond and last 2 times as long!