Buying Loose Gemstones: A Primer on the 5 Things to Know before Committing to a Purchase Get guidance from a certified gemologist and become wellversed in the basics of colored gemstones. Where diamonds have a globally accepted grading system and standardized certificates, colored stones have no such thing. On top of that, color is subjective which makes color stone grading more daunting. Learn these 5 best practices from a certified gemologist so you can confidently buy loose gemstones - without the overwhelm. 1. Get to Know the Names of the Best Quality Gemstones You may be surprised to know that there are other fine quality gemstones besides the well-known emerald, ruby and blue sapphire. But what other green stones can you think of besides the emerald? Did you know there are about 4 to 5 other high quality green gemstones out there?