i prefer sapphires myself
however this week i find myself making a diamond fold card for a card swap
and found that this tutorial was great but it was not suited to my sized card stock
so i made one up for you using a4 card and not a ruler in sight!
although you may want a bone folder to get those folds nice and crispy
get an a4 sheet of card and cut down the middle
fold in half gently-you just want the middle bits as a guide really for the next bit of folding.
fold 1 side down...like half a paper aeroplane wing
then do the other side-haha! a paper aeroplane!
unfold all your hard work thus far
turn it over and fold it the same way again
tada-another paper aeroplane!
unfold all your hard work AGAIN!
fold down the ends
-use the previous folds as your guide
squish them together making a valleys and mountains fold
see what i mean? do both ends
flick it onto its front and it should look like this
and the back bit should look like this
now all you gotta do is make it all purdy and noice and lovely
stay tuned to see what i did with mine