A gemmy crystal is a mineral crystal that looks like a gemstone - it's transparent or translucent, bright, and often has vivid color and well-formed faces. It’s not necessarily cut or polished like a gem, but it has the natural clarity and quality that make it look like one. Collectors often use "gemmy" as an informal compliment to describe particularly high-quality, eye-catching crystals.
For example, a perfectly clear, richly colored tourmaline crystal might be described as "gemmy" even if it's still in its natural form.
Natural crystals with gemmy characteristics are often rare, as their transparent, gem-like appearance makes them desirable for cutting into gemstones - meaning they often never make it to the fine mineral market.