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Ever wondered why sapphires can be so many different colors? Or why there are different hues of diamonds? It’s often assumed that diamonds and gemstones are mostly composed of the same minerals. This is not true though! The differences in diamond and gemstone mineral compositions are why they all have unique colors.
Here’s a look into what gemstones are, and how they get the exceptional colors that we find so fascinating.
Many gemstones are rare minerals of the purest quality. These gemstones are created from a variety of minerals that are buried deep in the earth’s layers. The intense heat and pressure force the minerals together and compress them over time, forming crystals. When other elements are present during the crystal formation that affect the color of the gemstone crystal, they can be called “impurities.”
The wavelength of the light refracted off an object is what makes color. White light contains all colors, like daylight. When white light touches an object, some wavelengths of light are absorbed by the object and some are refracted, or separated into its spectral colors. This refraction is what appears to the eye as color. This works the same way for gemstones. Different minerals absorb light in a different way, so gemstones made of different minerals will appear to us as different colors based on what light they absorb and refract.
Impurities in the gemstone can also affect how the mineral absorbs light, and therefore the color of the gemstone. For example, when it has no impurities, the gemstone beryl is colorless. But when chromium appears in the composition of the stone, beryl looks green, and with manganese it will look pink.
Rubies are a form of an aluminum oxide-based mineral called corundum. When this mineral is primarily red in color, it’s called “ruby,” but when any other color is noted it’s called “sapphire.” The color ranges in rubies from pink to dark red. These pinker shades are on occasion called pink sapphires if the red isn’t intense enough. There is opposition to this though, as some people refer to all pink and red stones as rubies. Rubies get their red color when the element chromium (chrome) is present. Although on its own chromium is silver-grey, when compounded, it can be exceedingly red.
Rubies are rated a 9 on the Mohs scale of mineral hardness, and are the second hardest mineral to diamonds. Artificial rubies are used in technology for lasers and timepieces, and are somewhat easily manufactured.
Sapphires (also a form of corundum) host a variety of colors including, yellow, purple, green, orange, and even multicolored or colorless. Most sapphires are blue, and this color is so often associated with the gemstone it’s often referred to as “sapphire blue.” A variety of minerals like iron, titanium, chromium, copper, and magnesium are the reason for the gemstone’s variety of colors. Sapphires are just as hard as rubies as a 9 on the Mohs scale. While mostly popularly used for jewelry, sapphires can also be of use in technology and timepieces.
Emeralds are a variation of the mineral beryl, unlike rubies or sapphires. Its signature green color can come from either chromium or vanadium. Emeralds are much less hard than the previous gemstones, and they only place a 7.5 to 8 on the Mohs scale.
With a 10 on the Mohs scale, diamonds are the hardest mineral that occurs naturally. Without impurities, the carbon crystal is transparent and colorless. With the inclusion of various impurities, diamonds can appear in several hues.
While these elements can cause a variety of colors, structural abnormalities can create color in diamonds as well. If the crystals aren’t in perfect order, some light is refracted which can cause pink, red or brown coloration.
The San Diego Gemological Laboratory is here for all of your gemstone, jewelry, and watch appraisal needs. Contact us today to get your valuables independently appraised by our accredited jewelry appraiser, Elliot Grunwald!