Colored Gemstones: How Do Gemstones Get Their Colors

Visible color change in a gem

If there is anything that most people like about gems, it is their gorgeous color. I know that there is a lot to it, such as their brilliance, the materials from which they form naturally, the billions of years they take to form, the kind of extreme temperatures that aid their formation, the energies these little treasures possess, and many more, but colors in gems are like ' love at first sight. It makes you fall for it before even touching it.

 

Mother nature can be very bizarre; imagine producing tiny shapeless colorful objects that are so valuable to make humans dedicate their lives to finding them, digging kilometers deep into the crust, and blasting all the hard rocks to find them.

From colorless to violet, nature has got it all, and that is why we'll never fully understand nature no matter how hard we try because there is always a new brand package nature has got ready for us.

In this article, we'll look at how gemstones get their colors, why, and what causes the different colors.

Why do gems differ in colors?

The color change among gemstones is caused by the light they reflect and absorb. In a more detailed way (How Do Gemstones Get Their Colors?n.d.), when light is flashed on a crystal, some light is absorbed, and some are reflected. The reflected one is what our eyes can see, and that reflected light causes the color change we see. 

For example, a diamond is white or somewhat greyish, but when white light flashes, such as natural daylight, which contains all the rainbow colors, the reflected colors are all we see. 

Diamond color change effect

A green stone is not usually green — it is because it has reflected off light that our eyes can see green. That explains why gems like emeralds can appear green, but when ground or smashed to powder form, the result is different as the green disappears.

Science states that the naked human eye can only perceive wavelengths from about 380 to approximately 750 nm. This means that if the different wavelengths of light go through a crystal, it will immediately look colorless. Notably, the gem will appear black if it absorbs all the light. However, if a rock absorbs all wavelengths in the spectrum, leaving the red part, it will look red.

 

What causes gems to differ in colors?

Gems form differently, and different impurities and inclusions affect a gem's way of reflecting light during that formation. Also, various crystals contain other chemical and atomic structures, so colors have to differ. This in gemology is described as "a stone being idiochromatic" or self-colored. A remarkable example of stones with this effect is the peridot which generally contains iron. 

Corundum such as rubies and sapphires are made of aluminum chloride; diamonds are typically made of carbon. This factor is a major one in the absorption of various wavelengths.

Such gems are allochromatic gems, which means that they absorb light due to the number of impurities and or the availability of elements in their crystal structure. An example of this effect is pure corundum. It is colorless, but it turns red when chromium portions are available, and it also turns blue when titanium portions are traced in the crystal.

Another thing worth discussing is the difference in colors among gems of the same type, such as topaz, spinel, etc. It happens due to impurities like chromium, vanadium, and many more. For example, in some gems like emerald, green is caused by amounts of chromium.

 

While this might be a factor in why green gems are green, it is not the same for corundum such as ruby. Chromium in rubies causes the color red. That's how the topic of 'colours in gems' is complex. Also, iron in sapphire causes a blue color.

Usually, most stones have a trace of elements like chromium (emerald, jade, ruby, topaz, and chrome tourmaline), beryllium (emerald), iron (aquamarine, yellow sapphire, chrysoberyl, green tourmaline, jade, and citrine), copper (malachite, paraiba tourmaline and turquoise), lithium (pink and green tourmaline), sulfur (lapis lazuli), manganese (spessartite garnet, morganite kunzite, and pink tourmaline, vanadium (color change sapphire, emerald, and alexandrite) and finally titanium (sapphire).

As I said earlier, the "colors in gems" topic is complex since you can tell by looking at the trace elements written above. The relationship between chemical impurity and gemstone color is also confusing because a single similar color can happen in different other trace elements. 

An example of this effect is the green of an emerald; it can be of chromium or vanadium or sometimes both.

Another confusing factor is that sometimes, one trace of elements can result in colors in different gem varieties. An example of this incident is chromium, it will result in red color in corundum but green in emerald, as the article (How Do Gemstones Get Their Colors? n.d.) says. 

External Aiding Factor

Some gems show their colors simply because of the surrounding environment, like a natural, incandescent light. For instance, green in alexandrite results from the natural light having much green light. It changes to other colors, such as red under incandescent light.

Electron Transfer of Ions Effect

A brownish color change effect

When a crystal absorbs specific wavelengths, a transfer of electrons amongst ions within a stone occurs; this significantly affects the stone's color, specifically sapphires.

Human Enhancements

An artificially enhanced crystal

One thing is sure humans, at some point, cause color changes in a stone. Some methods such as bleaching, heating, and many more can change a whole stone's color to deepen or lighten up.

Heat treatment changes the chemical state of impurity to either deepen or lighten the color or even decrease a specific hue. For example, the green tone in aquamarine can be improved by heat for clarity.

 

Pleochroic Effect

Pleochroism is the ability of a stone to show different colors when viewed from different angles; this affects the color change in a rock, for instance, tanzanite. Tanzanite can show a blue at a certain angle and violet when tilted to another angle.

References:

How Do Gemstones Get Their Colors? (n.d.). Leo Hamel Fine Jewelers Blog. https://www.leohamel.com/blog/index.php/2017/01/gemstones-colors-buy-sell-jewelry-san-diego/#:~:text=It