INS 553 (iii) is talc, numbered E553b in Europe. INS 553 covers the magnesium silicates: (i) is synthetic magnesium silicate, (ii) magnesium trisilicate and (iii) talc, the one taken from a natural mineral. Talc is a hydrated magnesium silicate and the softest common mineral; for food use it is mined, purified and finely ground, and food-grade talc must meet its own purity specification. Codex lists it as an anticaking agent, glazing agent and thickener, with dusting, coating and surface finishing among its purposes.
Its slippery, plate-like particles stop powders and pressed pieces from sticking to each other or to machinery. That makes it useful in pressed tablets and as a light dusting or polishing agent on some sweets.
The Royal Chitralada Milk Tablet lists talc and silicon dioxide together as anticaking agents, a common pairing in pressed tablets that keeps them from sticking and caking.
