While the term trapiche is usually used in reference to a trapiche emerald, the term by itself can refer to a few other things. The term trapiche by itself refers to a type of mill used to grind sugar.
Emeralds are not the only gems to show this particular growth form, though they were the first ones to be documented with this fascinating structure. There are also certain requirements that potential trapiche gems must meet. The crystal structure of a potential trapiche gem needs to be extremely symmetrical, otherwise the crystal just grows all-over the place.
Other gems that can potentially show a trapiche include sapphires, rubies, tourmaline, garnet, spinel, aquamarine (another type of beryl like emeralds), and quartz. An important note for quartz is that the potential trapiche feature extends to its other varieties, meaning you can have a purple trapiche from amethyst.
The quality of trapiche gems other than emeralds is up for debate, since comparing different crystals like emeralds and amethysts is not a fair comparison for either. These gems are made from different elements, with quartz being SiO2 and emeralds being Be3Al2Si6O18. The way these elements are arranged in a crystal structure is completely different too. Furthermore, are they being compared purely to other trapiches or any possible type of gem? It’s a gemological comparison of apples to oranges.
The quality of these other types of trapiches varies, since their appeal lies in the unique crystal formation instead of in their clarity. However, they are still comprehensively judged by color, clarity, and size for collector purposes. Purely in terms of crystal formation, emerald trapiches are the most distinct when the crystal formation is good. Poor crystal formations mean lumpy, and frankly unrecognizable specimens.
This makes little difference to individuals like gem cutters so long as the crystal itself is pure and clear. For gems like rubies that often form shallow and difficult to cut crystals, this can actually be beneficial to a cutter. Laboratory gemologists can find these more common samples useful too in terms of a database to compare other gems to.
Just browsing through the photos that come up for trapiche gems, a number of fake trapiches show up. Many look like they had arms drawn on with a magic marker, while others look like pieces of glass arranged in cement. They are extremely cheap in terms of trapiche specimens but severely overpriced for what they actually are, which makes them fraudulent.
Aside from the unrealistic growth characteristics obvious to any geologist and mineral enthusiast, a trapiche gem that big and perfectly clear will also come with a report from a credible lab you can verify with.