I'm interested to check whether this is right. I've heard, if we break an object, or something, into pieces, or cut it, devide it into two pieces,etc. and the new items still have the same quality, or can be recognised as the original material, then it's an uncountable noun! For example, if you cut some bread into pieces, the new items are still "bread". So, "bread" is uncountable. While, if you break a pen, the new items are not pen any more...
This is what once I heard would be great when teaching countable/uncountable nouns.
(Other examples would be: milk, sugar, chalk, etc. for which this rule works.)
Hope somebody will corrcet me, please!