1. An acid obtained from seaweeds containing sodium salt and used as a thickening agent for foods; such as, ice cream, and in dentistry where it is mixed with water and used as an elastic impression material.
2. Salts of alginic acids, occurring in the cell walls of some algae.

Commercially important in food processing, swabs, some filters, fire retardants etc. Calcium alginates form gels. Alginic acid is a linear polymer of mannuronic and glucuronic acids.