Well, you ask questions that are general in nature. Birthstones are very commonly semi-precious stones. There are lists common to the internet. Values can be ascribed generally but as you no doubt know Diamond is very valuable and so is emerald, sapphire and ruby, while topaz, aquamarine and amethyst and others are not so expensive. Quality can be determined by size, weight, clarity, color and rarity. Impossible to determine as vaguely as your questions have been phrased. More info available on the internet.