For my blog entry I decided to research how and why gemstones are certain colors. Upon doing reading, I discovered that the color in the gems is actually due to impurity ions with other elements. Some elements such as Iron, Chromium, Titanium, Manganese, and many others cause color in minerals. For example, a ruby that contains less than one percent of Chromium will be a red color, but if the ruby has no Chromium will have no color at all.
The intensity of the gem color is also correlated to the amount of the impurity it contains. For example, Beryl that contains Manganese (Mn) is a pink color when it has Mn++ ions in it. However, Beryl with Mn+++ ions in it is red. Therefore with the addition of more positive ions, the color is intensified. However each element ion is not specific to a color, since the same element will turn different gems to different colors. To use Chromium as an example again, in a ruby the Cr+++ will show up as red. However, in beryl Cr+++ will appear emerald green, and in alexandrite its is a purple red color.
Another type of color variation is called a Color Center. This is a color of the gem due to imperfections in the color causing element usually due to damage from radiation. These radioactive waves cause some of the electrons in the atoms to separate due to excess energy and relocate at a new place, which causes an imbalance in the ions there, creating a Color Center. These chemical processes are the cause of visible colors which we see in minerals and gems.
source: http://socrates.berkeley.edu/~eps2/wisc/Lect7.html#Perceive
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