Both of the previous answers were for Platinum, not for Pearl. In Diamond/Pearl, there is a house near Pastoria City where there is a person who used to work for the Weather Institute of Hoenn. She is reminded of that by the shards (for some strange reason, even though it is believed that the shards are connected with the plates) and for ten of the same color shards will give you a corressponding weather move, such as ten red shards for a Sunny Day. Or you can just sell the shards.