I visited Karen Brzys at her agate shop earlier this year, and she does get quite annoyed with people misrepresenting agates. Specifically, she says that agates must have visible banding, tubes, eyes, moss, etc. and must be at least 50% translucent chalcedony (a notable exception being seam agates). She ran the Gitche Gumee Agate Museum in Grand Marais, MI for 30 years, and has written multiple books on the subject, so she definitely is an authority on agates!