Alum salts (Aluminum sulphate) are used for protection, luck and to stop gossip.
Alum is used for protection from gossip, for money luck and for legal work.
Some ideas for magical uses:
Add a small chunk of Alum, three cloves and a sprinkle of sugar to a red flannel bag to create a Gossip Stop mojo.
Break into small pieces and sprinkle around a Gossip Stop candle.
Set a chunk of Alum on an altar to protect from jealousy.
If someone is going to testify against you in court, write their name on a piece of paper wrap it around a chunk of Alum and put it in the freezer to keep their mouth shut.
(Alum is an emetic. Avoid ingesting.)
For in-depth information on how to use this and other herbs and roots magically, I recommend Hoodoo Herb and Root Magic and Cunningham's Encyclopedia of Magical Herbs, both of which can be found in our Books section.