The smallest marble size is the Itty Bitty at approx 0.45" or 10mm. This is the diminutive marble, cute and elegant. The Itty Bitty marbles are solid color translucents in 8 vibrant colors: red, yellow, green, royal blue, turquoise blue, iridescent royal blue, iridescent clear, and one opaque orangy/red. Buy some Itty Bitty semi-precious gemstones or "gem marbles" to add even more variety to your options! Sold separately.