Prasiolite, also known as green amethyst. Its striking green color results from the heat treatment of naturally colored purple amethyst. While natural prasiolite is very rare, almost all commercially available prasiolite has been heat treated to produce its green coloration.
In nature, prasiolite only forms when amethyst undergoes heating from nearby volcanic activity or other geothermal events. Such naturally occurring green amethyst is so uncommon that it was not recognized as a unique variety of quartz until the 1950s. The vast majority of prasiolite in jewelry and on the gem market today is created artificially through controlled heat treatment processes in laboratories or specialized facilities.
The most coveted and valuable prasiolite is that which retains some of the original purple amethyst color zoning and patterns in addition to areas of green. To produce such dual-color stones, heat treatment must be carefully regulated. Lower heating between 150°C and 400°C for several hours will result in a green color concentrated around inclusions or color zones. Higher temperatures between 500-600°C applied for shorter periods will uniformly transform the entire crystal into green prasiolite.
While heat treatment sounds like an artificial process, it is in fact simulating the natural conditions that originally produced the first prasiolite specimens. Controlling temperature exposure allows the green color to be predictably and efficiently created in amethyst sourced from geologic deposits around the world. Heat treatment is also a stable and permanent alteration – prasiolite will retain its green color indefinitely after the heating process.
In addition to bringing out green hues, heating also causes structural changes in the amethyst. The heat removes certain iron impurities inside the crystal and makes the stone harder and denser than untreated amethyst. Refractive index, specific gravity and luster also increase after heating. All of these effects combine to produce the vivid green prasiolite that is so highly prized in jewelry settings.
So, yes – commercially available prasiolite has essentially all been heat treated. This process artificially simulates the natural conditions that create this rare green variety of quartz. Heating amethyst to produce prasiolite has made this uniquely colored gemstone more available and affordable for jewelry purposes. Next time you admire the crisp green tones of a prasiolite gem, you can be sure its desirable color came from the hands of skilled heat treatment craftsmen. Prasiolite's signature green would not be possible without the transformative power of heat on originally purple amethyst stones.
