Rite ive played through this once but that was a while ago doing none of the extra stuff etc. Now im playing through again and need reminding about these.

Where are the 3 huge materia, one you get from doing the train incident on disk 2. What about the other 2?

When materia masters it duplicates itself yes? Does all materia do this, ive read some dont, eg KOTR?

Does "Master" materia (eg master summon) duplicate itself when mastered, im thinking this is a definite no?