Beryls are a gorgeous group of gemstones owing to their clean crisp tints. Think aquamarine, morganite, heliodor, even that teensy rosy bixbite.
To the cognoscenti, the line is drawn between emerald and green beryl on matters of saturation and light--or richer greens. The deeper more intense greens toss the stone in the emerald group. Ideally an emerald is recognized by a strong deep green, and often with a very slight bluish back color. However, some Brazilian emeralds reveal an ever so slightly yellow secondary hue.
Green beryls are their own enviable gem however, and not considered a second fiddle to emerald. Take, for instance the alluring green beryl ring designed by Christian Dior, part of their 'Incroyables et Merveilleuses' collection. A ring like this sold at Christies Hong Kong last year for $42,135US against a pre-auction estimate of $10-$15K. Goes to show you what Asian bidders --who are savvy color stone collectors thought about this 'incredible and marvelous' ring.
The large and ever so clean green beryl crystal from the Smithsonian Institute gives one a closer view of what these lighter stones look like in the rough. Emerald that size would be much darker, maybe even semi-transparent, and true to its nature, often loaded with telltale percussive fracture inclusions.
Both of these verdant gems are treasured by collectors, and it's a personal preference as to which one is more appealing. Fortunately for green beryl fans, the price is more appealing than emerald.