Garnet is not one mineral but a group — several silicates that share the same crystal structure but differ in what fills it. The common red-orange stone is almandine, and the deep wine colour comes from iron and aluminium in the structure.
Small beads are used more often than large ones for garnet, partly because the material is often found in smaller crystals and partly because a 4 mm strand with many beads reads denser on the wrist than a 10 mm strand. This is one of the harder gem materials, so it wears well.