Why are there so many colors of minerals?
We share a whole lot of mineral images on this page, many of which would qualify as gemstone if the stones are pristine enough. One great question for anyone who deals with minerals or gems is…where does the color come from?
Many minerals, when they are pure, are either completely colorless like quartz, or a single strong color, like hematite which will be dark black when found as a chunk. But on the other hand, there are minerals like corundum (aluminum oxide) which can be colorless, bright red as a ruby, blue as in a sapphire, or even pink and orange as in the rare Padparadschah.
The scientific definition of a mineral is that it is a solid substance found in nature with an atomic structure that is consistent and repetitive over a distance. In other words, it is a crystal made up of atoms put together in a constant sequence.
The key to the color for many minerals, as explained in this chart, is found in that setup. A single crystal is made up of a huge number of atoms. Sometimes, when a crystal grows, it can substitute the wrong atom into a spot; iron going into quartz for the silicon atom or chromium going into corundum in place of aluminum.
These impurities can fit into spots in crystals some, but often not perfectly. They may vibrate around or they may bond incorrectly with the surrounding oxygen atoms, changing how the electrons in the structure join together.
Electrons are the keys to color. When electrons are able to move within the structure of minerals, they are able to absorb light and create colors that we are able to see.
This chart outlines how color forms in many common minerals and gemstones. Almost all of them follow a certain format; the wrong element goes into a crystal in a small amount, creating unpaired or mobile electrons that interact with light passing through the crystal structure.
-JBB
Image credit: Compound Chemistry (creative commons license): http://www.compoundchem.com/2014/06/29/what-causes-the-colour-of-gemstones/