Diamonds come in a variety of colors and their colors are caused by various factors.  Trace elements, inclusions, radiation, electron changes and  post-growth plastic deformation while travelling to the surface.  

Yellow: Nitrogen

Red: Electron Changes (I am personally not familiar with this research and will look into it)

Orange: Nitrogen again!

Green: Radiation from nearby rocks that alters the electrons

Blue: Boron

Purple:  “..post-growth plastic deformation while traveling from the earth’s mantle to its surface via magma.”

Pink: Plastic deformation

Grey: Boron and other trace elements

Brown: Nitrogen and structural defects which cause distorted light refraction

Black: Inclusions of metals and graphite. 

THIS LIST DOES NOT INCLUDE ALTERATIONS BY MAN BUT ONLY WHAT IS FOUND IN NATURE.

History:

Lapis Lazuli has a long long history dating back to ancient Mesopotamia, Egypt, Greece, etc. where it was traded and prized.  It was one of the most valuable and regarded gems across the world for thousands of years, used in art, practical items, jewelry and ceremonial objects.  To give an example as to it’s long history, for over 6,000 years it has been mined in what is now modern day Afghanistan.  

Important information:

Because of it’s long history, Lapis is considered a “gem” but is actually a rock composed of “lazurite, calcite and pyrite. Lazurite, a complex mineral containing sulfur, is the essential ingredient of lapis that gives it its vivid blue color. Calcite is calcium carbonate, a white mineral responsible for the white streaks in many specimens of lapis. Pyrite is iron sulfide, which is white-gold in color and lends lapis its distinctive glitter.”

Fun Facts:

Cleopatra is said to have used it as eye shadow and crushed lapis was used as a blue pigment called ultramarine from Medieval to Renaissance times.  

Science: 

Refractive Index: 1.500, sometimes 1.670

Color : Greenish blue to violetish blue

Mohs Scale: 5-6

One of the newest gemstones on the scene, tanzanite was only discovered in 1967 and only exists in the hills of Merelani in northern Tanzania.  It’s gem quality Zoisite and was initially popularized and distributed by  Tiffany & Company.  Heating can turn other colors of the stone like brown or green into the brilliant blue color thats most popular making it commercially viable and available.  

Tanzanite displays “ pleochroism, which is the ability of a gemstone to show different colors when viewed in different crystal directions.”  This influences how it’s cut because of the balance between the size and color of the stone since vivid blue is the most valuable. 

“ The blue color of tanzanite is caused by small amounts of vanadium within the zoisite mineral structure. When vanadium-bearing zoisite is heated to a temperature of 600 degrees Celsius for about 30 minutes, the oxidation state of the vanadium is changed and that change causes or improves the blue color. “

Chemical composition of Ca2Al3(SiO4)3(OH), a refractive index of 1.691 to 1.700 and a Mohs Hardness of 6-7.  It’s the birthstone for December.  

Smooth and Rough amber shown above. 

Amber is a gem but not a gemstone since it’s organic.   It’s chemical formula is C10H16O and a comes in at a low 2.0 to 2.5 on the Mohs scale.  

Amber has been carved and made into jewelry and ceremonial objects as far back as 11,000 years ago.  In fact, “ The decorative use of amber culminated in 1712 with the completion of an entire banquet room made of amber panels constructed for King Frederick I of Prussia.”  To this day it’s regarded as having healing powers by those who practice forms of Wicca and crystal healing.  

Originally part of a trees defense system, the resin (AKA sap) fossilized over millions of years to produce the rough gem we know today. Whenever a tree is damaged, it leaked out the resin to protect itself and under rare conditions, the sap fossilizes and is preserves.  

Inclusions in the amber are varied but also include organisms and organic material from many extinct species (first photo). The movie Jurassic Park popularized amber even more because it postulated that DNA would be preserved inside the amber and species could be cloned from it.  Unfortunately, DNA is an inherently unstable molecule and degrades even while sealed in amber.  

Fake amber flakes while real amber turns to powder when rubbed on a knife.

Peridot is the August birthstone and so deserves a post in the beginning of August.  The word peridot comes from the Arabic “faridat,” which means “gem.” Most peridot was formed deep inside the earth around subduction zones  and was delivered to the surface by volcanoes.  Pakistan and Myanmar are said to be where the best gem quality peridot comes from.  

Other than being a birthstone, peridot (aka chrysolite)  is gem quality olivine  that has been made into jewelry since ancient Egyptian times.  The Romans, and for a brief time Medieval Europe, valued the stone and thought it’s beauty worthy of being a treasure.  

“ Some historians believe that Cleopatra’s famous emerald collection might actually have been peridot. People in medieval times continued to confuse peridot with emerald. For centuries, people believed the fabulous 200-ct. gems adorning the shrine of the Three Holy Kings in Germany’s Cologne Cathedral were emeralds. They are, in fact, peridots “

 The green color comes from the amount of iron present in the stone and only comes in green compared to most other gemstones that display more variety.

Fun Fact: Peridot is also found in meteors that fall to earth and they’re sometimes large enough to be cut into gems.  

Chemical formula:  (MgFe)2SiO4

Moh’s hardness:    6.5 to 7

Some gemstones are exposed to radiation in a reactor to change/enhance their color.  This makes the gemstones slightly radioactive (except in the case of gamma rays) and therefore fall under control of the United States Nuclear Regulatory Commission (NRC).  Irradiation, “..can take place in a nuclear reactor (neutron bombardment), an accelerator (electron bombardment), or by exposure to gamma rays in an irradiator.”  The stones are then set aside for a couple months to allow for enough radioactive decay to make the stones safe. Pictured above is a common example of orange topaz turning blue as a result of being exposed to radiation.

the “ The most striking aspect of a colored stone's beauty is its color. It is this feature which the cut is intended to enhance. However, a faceted colored stone does not just display a single uniform color when viewed from above. Instead...it displays three varying shades of the hue. These three color variations result from three different phenomena: brilliance, windows and extinction.”

Extinction:

“ Basically, a gem quality stone is 100% color and has no extinction. As extinction increases, value goes down more rapidly at first and then more slowly as black becomes a large part of the color. Extinction is a nonlinear effect, almost as strongly so as modifier (saturation).”  - Patterson (1982)

“ Extinction is areas of darkness visible when the stone is judged for brilliance. It is caused by blackness in the stone and the proportion angles. “ -  The colored stone grading course workbook of the Gemological Institute of America (GIA, 1983)

Brilliance:

“Brilliance refers to a return of light to the eye when a gem is viewed from above. The amount of brilliance that a gem displays if free of inclusions is mainly a function of two things: the angle of the pavilion facets and the stone's critical angle (which is inversely proportional to the refractive index of the stone). Because it is primarily the size and angles of the pavilion facets that are responsible for influencing these phenomena, only the pavilion is shown in the following illustrations. “

Window:

Results from the light passing through the stone and not being reflected back at the eye.  Resulting in a clear window where the stone’s color turns dull and unappealing.