Moss agate is form of chalcedony. It does not actually contain organic matter, the green color comes from green minerals. It is not considered a true agate as it lacks agate's defining feature of concentric banding.
There are many types of obsidian found through the world. This type, called fire obsidian, without a doubt is some of the most colorful and most rare of them all. It can rival the very finest of precious opal.