Aura Quartz and other Aura products often get lumped into the "Dyed" category of treatments, however there is a lot more to the process. Many stones have been given the Aura treatment, such as Fluorite, Howlite, Agate, and others. For the purpose of this, I will be focusing on the treatment of Quartz.
Briefly, Aura Quartz is a treatment applied to the surface of the stone to give it incredibly bright and mostly un-natural colours. It is mostly stable, and is unlikely to wear off the surface, but doesn't penetrate the into the stone. This means if you were to cut it, the colour would not stay.
The process that these stones go under for this treatment is a little secretive, however the basic procedure for quartz is as follows.
The material set to be treated is placed in a vacuum chamber, and then heated to over 800 deg C (1600F). Particles of metal are then jetted into the chamber, where they fuse with the surface of the stone. Many different metals are used in this process to give different colours.
Angel Aura Quartz - Coated with Platinum & Silver
Apple Aura Quartz - Coated with Nickel
Aqua Aura Quartz - Coated with Gold
Lavender Aura Quartz - Coated with Titanium & Indium
Rainbow Aura Quartz - Coated with Titanium
Rose Aura Quartz - Coated with Platinum & Silver/Gold
Ruby Aura Quartz - Coated with Silver & Gold
Sunshine Aura Quartz - Coated with Iron
Tanzine Aura Quartz - Coated with Gold, Indium, & Niobium
As I said at the start, this process is a little secretive, so some of the metals listed may be incorrect, or not the full range used. There are also new colours and mixes being developed, so this isn't the full list. I hope to one day have all of the available colours, however that is probably a way off. The depth of colour can also be changed by the purity and amount of the metal used, which is why some types can range from dark, right through to the lightest colour.