Skin Color

A person's skin color is determined by the amount of melanin in the skin, which is the skin's pigment. The greater the amount of melanin, the darker a person's skin will be, ranging from nearly pure white to almost black. Some people, known as albinos do not have any melanin in their skin, causing it to be actually white, with only a pinkish tint due to the blood in the skin.
Melanin is present in human skin because it helps protect against an excess of harmful UV rays. As a person's skin is exposed to the sun, more melanin is produced, causing a darker overall pigment, and therefore the appearance of a "tan". If a person is wearing clothing such as a t-shirt, the melanin will not produce more in that area since it is already being protected from the UV rays by an external source, thereby resulting in what we commonly know as a "farmer's tan".
Variations in skin color date back to early evolution times, when humans hadn't yet evolved from chimpanzees in Africa. When the standard light-skinned dark-haired chimps started to evolve and lose their hair, over time and evolution their skin became darker to help protect against the very UV intense region of Africa. However when humans eventually began to migrate further north where the sun exposure was less intense their skin evolved back to being more pale, which would allow them to absorb the needed amounts of vitamin D. This biological and evolutionary process is what skin color is grounded upon.



sources:
http://en.wikipedia.org/wiki/Human_skin_color

Color in Gemstone Minerals

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