April Fools' Cobble (1 in 13)

When the pack is active, random cobblestone blocks appear to be blocks of diamond.
['Random' works like lillypad orientation — with a specific x,y,z block always showing the same.]

This variation of the pack has 1 in 13 blocks affected
Two other options exist should a different degree of replacement be wanted:
April Fools' Cobble (1 in 169)
April Fools' Cobble (1 in 1014)

As usual, for versions 1.14 through 1-20.1, activating the pack will produce a warning that it was made for an earlier version…
this can be safely ignored.