Now that's a Stone of a Different Color!

Have you ever wondered what gives a colored crystal it's color?  Well I have.  And I have the answer for you, or rather answers, as there are several factors that cause a crystal to change it's color.  Crystals get their colors from energy band gaps, physical phenomena, the structure of the mineral, the shifting of electrons, charge transfer action caused by a transition metal impurity (charge transfer occurs when electrons uses light energy to shift from one type of atom to another) and irradiation or other energy sources have disrupted it's atomic structure creating a "color center".

For this weeks blog we will focus on "Color Center" Crystals.

Color Center minerals have one of two defects.  In one case, they are missing electrons or have electrons out of position.  Both leave an empty spot in the orbital arrangement of the atoms.  In the other, electrons of mineral impurities have replaced some electrons of a normal element in the mineral's chemical composition.






Chem Class Reminder:  Electrons are a form of energy and any additional energy might get them to shift their position, especially if they are out of place to begin with.

In some flourite (calcium flourine cesium), a rare earth element gets into the same structure, resulting in a charge-transfer situation that produces the colors blue and pink.  the problem with color center minerals is that it is unstable.  It's color is easily lost upon exposure to heat, strong light or radiation.

Amethyst is a perfect example of this.  The luscious violet amethyst has an unusual electron configuration:  Iron ions, valence 3, get into the structure of the quartz, coloring it a lovely yellow.  however if yellow or colorless quartz are subjected to enough outside radiation, some of those valence 3 iron atoms will pick up errant silicon or oxygen electrons that have been ripped from their normal position.  Voila!  Just like that we have ourselves a beautiful violet colored crystal.

Not all color center minerals are unstable, some of them keep their color as their impurities are not energy sensitive.  Allowing them to retain their colors despite outside heat or radiation.

It is endlessly fascinating to me how, what appears to be a shiny colored rock goes through all these natural processes to get where it turns into a "stone of a different color".