get on the tilemaster 2 day training course, brilliant course and teaches you all you need to know about stone and tile id, you'll learn loads more as well but ID is the most important. It will also help you decide if its for you or not,
Stone floor is fast becoming my number one money generator,
As you get more knowledge about stone you'll be able to sell it easier. my confidence is getting bigger everyday and its starting to show when i quote, got 4 out of 6 this month and we aint cheap.