first, i don't think there will be two of the same type in one game (crystal & stone)
crystal's weapon is a bouncing projectile (rebound striker, gemini laser)
individual robot masters have individual weaknesses, so ice man will not be weak to fire
weapons have a type that coincides with said individual weaknesses, determining what robot master they are effective against
i gotta get my take on this in :/
Fire: Fire, Heat, Pharaoh, Flame, (Magma, Solar)
Nature: Wood, Snake, Toad, Plant, (Search, Hornet, Sheep)
Aquatic: Bubble, Dive, Wave, (Aqua, Splash, Pump)
Cutter: Cut, Metal, Shadow, Tomahawk, Slash, (Sword, Blade), Punk
Bomb: Bomb, Crash, Magnet, Drill, Napalm, Burst, (Grenade, Commando), Ballade
Spacetime: Time, Flash, Bright, Gravity, Centaur, (Astro, Galaxy)
Reflection: Gemini, Crystal, Knight, Spring, (Strike), Enker
Poison: Oil, Dust, Junk
Electric: Elec, Spark, (Clown, Plug)
Air: Air, Gyro, Wind, Cloud, (Tengu, Tornado)
Speed: Quick, Top, Charge, Turbo, (Nitro)
Needle: Needle, Yamato, Quint
Ice: Ice, Blizzard, Freeze, (Frost, Chill)
Earth-mover: Guts, Hard, Stone, (Concrete)
Normal: Ring, Skull, Star, Shade, (Jewel)
just because a robot master is one type doesn't mean their weapon is the same type
EDIT: Welp, someone posted after me :/