is it for science...
1)Table Salt : Once of the most widely used salts, table salt goes through a refining process that removes traces of other naturally occurring minerals. Chemical additives such as sodium silicon-aluminate, calcium phosphate, or magnesium carbonate are sometimes blended in to prevent clumping. Table salt and iodized salt are preferred in baking for their fine-grained texture and accuracy of measure.
2)Rock Salt : Sold in large crystals, rock salt has a grayish hue because it is unrefined. Rock salt makes a great bed for serving oysters and clams. Or combine it with ice to make ice cream in hand-cranked ice cream makers.
3)Kosher Salt : This inexpensive coarse salt is evaporated from a brine, usually under specific conditions approved by the Orthodox Jewish faith. It contains no additives or added iodine. Kosher salt is popular among chefs because its coarse texture makes it easy to pinch up between you fingers and sprinkle onto foods. Measure for measure, 1 teaspoon of kosher salt contains less salt than the same amount of table or iodized salt.
4)Iodized Salt : A form of table salt, iodized salt is fortified with iodine that was lost during processing. Iodized salt was the first "functional food", fortified in the early 1920s in response to a Midwest-focused epidemic of gioter (hyperthyroidism) that was caused by iodine deficiencies.
http://www.asianonlinerecipes.com/food_articles/different-types-salt.php