So since there are two spells that allow us to make permanent special sand lets see how many fun ways we can think of use them. It is also available "naturally" in waste land locations if you can't use the spells to make your own and Black Sand at least can be used to create more of itself as each creature killed by it crumbles into more of it. I assume its the equivalent weight in sand but could be 1/2 or 1/3 of that depending on if the DM rules that water in the body dries away leaving only the physical material to convert. The description of the transformation isn't very explicit.
Black Sand (Sand, pg 111)
Cleric 3, Sand 2 [Necromancy, Evil]
This spell creates an area of sand that does 1d4 points of negative energy damage per round, not a lot but there is no save after the initial casting. The fun part is any creatures that are killed by this energy crumble into black sand themselves. The common thought is that the sand made from the body is permanent and would remain after the spell's effect ends.
Slip Sand (Sand, pg 121)
Druid 4, Ranger 4, Sand Shaper 3
This spell converts a 10ft cube/level of sand into Slip Sand, a region of frictionless sand that serves as a magical trap. The duration of the spell is permanent and not dismiss-able. Under that assumption any sand gathered from the trap would retain the same properties.
What kind of fun could you have with the sand in question?
Black Sand is perfect for undead or Tomb Tainted characters to use as a source of Fast Healing at 1d4 per round.
With adhesive you could roll the ends of your arrows, bolts, or other ammunition in Black Sand to add an additional 1d4 points of negative energy damage/round to your attacks.
Use Black Sand to poison an assassination target, sprinkle some on their poppy seed muffin or in their pepper shaker. When injested it should slowly kill the target for 1d4 damage per round until they die and crumble into Black Sand themselves.
Slip Sand could be used as a less obvious means of greasing a floor.
Use sovereign glue to make a sandpaper layer of it on the bottom of your sled to make it pull more easily across the ground.
Do the same to coat the outer layer of your armor for a bonus on escape artist and grapple checks.