Discovered in Greenland in 1896, Hackmanite is a vibrant pink variety of sodalite,
This unusual stone faded to colorless when brought to light. it returns to it’s original color when left in the dark for an extended period of time, or when exposed to short wave ultraviolet light. This ability is called tenebrescence or reverse photochromism. (This is what happens to eyeglasses that darken or lighten when exposed to different lighting.)

This variety of sodalite was named Hackmanite after Axel Hackman, a Finnish geologist with the University of Helsinki.

What I find fascinating about Hackmanite is that the color change in hackmanite found in Quebec and Greenland changes from pink or violet to white, yet the Hackmanite found in Afghanistan and Myanmar changes from creamy white to pink, red or violet in sunlight! It reverses….why is that??  When heated though, you kill the color change altogether.

Natural colors in the dark

Researching Hackmanite I got a little side tracked, wondering what causes the color change in some minerals but not in others. Apparently something called F-Centers are the cause.

An F-Center is a defect in an ionic lattice (a structure of millions of atomic formations of an ionic substance, structured like building blocks into a three dimensional formation.(Wiki answers) This defect occurs when an anion leaves as a neutral species,leaving a cavity and a negative charge behind. (An anion is an atom that has gained electrons. Since they now have more electrons than protons, anions have a negative charge.They are termed so because they get attracted towards the anode or positive electrode (Thanks wikipedia) The negative charge left behind is shared by neighboring positive charges in the lattice.
In Hackmanite it is believed that some of the negatively charged chlorine atoms are missing,allowing free electrons to become trapped in the vacancies. This the basis of the F-Center. In Hackmanite this center asorbs green, yellow and orange light as well as some amounts of blue. There we have the cause of the various shades of Hackmanite and the fading results.

Got carried away with the chemistry lessons, sorry about that. The more you study natural things the more wonderful and fascinating the world becomes.

Hackmanite is the higher vibration of sodalite so all healing and spiritual qualities are considered to be much stronger, especially in the throat and third eye chakra, accelerating intuition and clairvoyant abilities.

Resources: Wipedia, Wiki answers, gemology online, Mindat.org