Flagstone and Slate are great for patios, walkways & decks.
If laying a flagstone pathway in an existing grass area, lay the flagstone directly on the grass in the desired locations. Check back in a few days, they areas under the flagstone should be tamped and easier to see where to cut out for the pieces.
Approximate flagstone coverage:
1" Flagstone = 14 LBS per sq.ft
2" Flagstone = 25 LBS per sq.ft