techian.com

ok
here we go:
> create a background document with your choice of color and size
> then create a cube (i hope you know how to create this)
> the cube will show its three faces towards you, each of them will be in different layers (say face1, face2, face3)
> now on each face apply bevel and emboss with chisel hard technique and full depth and size.
> now apply the color overlay of your choice (the color must be the color of the diamond you want), apply some gradient to make it some more attractive
> for the face which is at the top of the cube (say layer face3), don’t apply bevel and emboss and apply gradient of angle style
> now select all three face layers together, copy them and paste your copy into a new layer, this will put all the three faces in one layer (say singleface), disable the previous three different face layers (face1, face2, face3)
> now duplicate the single layer you just created, rename it as diamond
> copy the figure from layer singleface and paste it into a new layer, press ctrl+T (for free transform), rotate the pasted figure as you want, decrease the opacity of the new layer so that the diamond layer in the back can be seen also
> repeat the previous step as long as the figure in the layer diamond looks quite like a diamond
> now merge the newly created layers into diamond layer
> apply some inner glow and outer glow to diamond layer
> disable the singleface layer
> now you are done