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10 Most Common Colored Gemstones

Presidium Instruments - Everything You Need To Know About Diamond Testers

Although a diamond is usually the first thing that comes to mind when we think of cardinal gems or valuable stones, colored gemstones can actually be worth even more. Each of these gemstones has its own unique qualities that lend to its value. 

Here are 10 of the most common colored gemstones and the unique characteristics on which the beauty and value of each are assessed. Plus, we’re giving a lowdown on how to test colored gemstones using industry-trusted gemological instruments that can help to identify them, so read on!


A variety of aluminium oxide or the mineral corundum, rubies have a pink to blood-red or pigeon-blood color, which is attributed to the element chromium. One determinant of a ruby's quality is its color—the redder the stone, the higher its value. 

The Jubilee Ruby is the most expensive gemstone ever sold at auction in the US. It weighs 15.99 carats and sold for $14 million dollars (or $885,000 per carat). The buyer of this stunning piece had their own special request: they wanted it mounted on an 18k gold band and other rare jewels by Verdura.

To ascertain the value of rubies, first we have to identify its properties using a tool such as the Presidium Synthetic Ruby Identifier (SRI). It is a ground-breaking desktop device that instantaneously identifies synthetic (flame fusion) rubies through its characteristic high UV transmittance. It utilizes UV light with auto cut-off and gives quick results with clear indicator lights to measure the UV transmittance ability of ruby gemstones. 


Also a variety of corundum, sapphires contain trace amounts of iron, titanium, chromium, vanadium, or magnesium—the higher the iron, the darker the blue. However, there are other variants, including gray, black, purple, green, and a pinkish-orange called padparadscha. Sapphire and rubies are often found in the same locations

Sotheby’s Hong Kong sold a 27-carat blue sapphire for $6.7 million in 2015, which is the world auction record price per carat and 10x more than any other gemstone on earth! The Jewel of Kashmir is a striking emerald-cut cornflower blue sapphire weighing 27.68 carats set with pear shaped diamonds together weighing approximately 5/6th ounce (27 mg). 


Emeralds come in every color, but they're often identified by their greenish-blue hue. Some people think that only those with traces of chrome should be called "emeralds." Most gemologists and gemological laboratories likewise believe to call a gemstone “green beryl” if the color is “not green enough.” According to GIA, highly transparent emeralds with a consistent green coloring are the most valuable.

The world's most expensive emerald is sitting in a vault controlled by the Los Angeles County Sheriff’s Department. It weighs an impressive 752 pounds and is roughly the same size as a mini fridge. This behemoth of a gemstone has been valued at $400 million dollars. However, the Bahia Emerald has been embroiled in several controversies—including death, family dispute, and hurricanes—that many call it “a cursed stone.” 


Garnets come in almost every hue, but red and orange are the most popular and green (grossular and andradite) is the rarest. Its color is a garnet’s most important quality, and the biggest determinant of its price. Other garnet variants include those that are purple, yellow, and colorless.

The demantoid is the most valuable type of a garnet mineral. Its green color makes it stand apart from other garnets, as well its dispersion, which is comparable to that of diamonds. For years it had only been produced by Russia until new sources were discovered in the 1990s, including Namibia and Madagascar. Demantoids over 1 carat are very rare as these stones break apart easily when mined. Prices for Russian demantoid start at about $1,000 per carat.

For identifying sapphires, emeralds, and garnets, the Presidium Gem Tester II (PGT II), Presidium Gem Indicator (PGI), and Presidium Duo Tester II (PDT II) are among the most credible colored gemstone testers out in the market today.

The Presidium Gem Tester II (PGT II) is the industry's one and only handheld gem indicator and digital tester for application in 16 common colored gemstones. The probe consists of two linked thermometers: one which is heated electronically while the other is cooled by the gemstone being tested. The difference in temperature creates an electrical output, which is then amplified and displayed.

The Presidium Gem Indicator (PGI) is a pioneering handheld tester specifically for colored gemstones. It identifies up to 31 different types of colored gems based on their thermal conductivity and comes with the Presidium patented refined changeable probe tip, which ensures minimal equipment downtime. The PGI features a color input function that allows users to select from a range of 12 common colors. 

The Presidium Duo Tester II (PDT II) comes highly recommended by industry practitioners when it comes to colored gemstones. It is the only comprehensive tool on the market that combines two proven testing methods for gemstones, thermal conductivity and reflective indexes. Coated gemstones can also be generally tested with the PDT II. With the industry’s thinnest probe tip size of 0.6mm, PDT II tests gemstones as small as 0.02ct.


A rare and precious gemstone, alexandrite changes colors depending on its environment. Originally discovered in Russia’s Ural Mountains around 1835 by French mineralogist Pierre, alexandrite is often described by collectors as "emerald by day and ruby night."  Today it can be found all over the world with some excellent examples coming from Sri Lanka or East Africa.

The Whitney Alexandrite is  popularly known as the most prized of its kind. The gemstone, which weighs 65.08 carats, can now be found at The Smithsonian Institute. Its current market value is around $4 million dollars.

The Presidium Refractive Index Meter II (PRIM II) is a desktop digital tester that is used for the accurate measurement of broad-range R.I. values, from 1.000 to ~3.000, making it the ideal tester to use on alexandrites. The PRIM II can instantly identify colored gemstones without the inconvenience of using messy RI liquids. It comes with a complementary proprietary software to help users verify the type of stone based on various gemstone properties.


Amethyst is a violet variety of quartz that has been found in deposits all over the world. In olden days, it was considered one of the "cardinal" gems but with today's technology we can find amethysts anywhere. Nowadays, amethysts are considered a semi-precious stone, but they're still rather pricey-about $1-$5 per carat depending on quality. 


Tourmaline refers to a gemstone family that comes in almost every color, with some having more than one color in the same stone. Jewelers and gemologists use trade names for different colors of tourmaline such as rubellite (red), indicolite (blue), chrome tourmaline (green), schorl (black), and canary tourmaline (yellow). 


A gemstone popularly known for its yellow, orange, and brown color, the topaz actually comes in other colors and colorless variants, as well. The most valuable of types are the pink and red stones, followed by orange and yellow. The blue topaz used to be rare but its value has declined with the surge in supply. 



"The Black Prince's Ruby," which is part of the UK's Crown Jewels, and "Catherine the Great's Ruby," made for Empress Catherine II of Russia, are in fact, not rubies but both spinels. Sharing the same rich red coloring as rubies, a spinel has a characteristic octahedron crystal shape like that of back-to-back pyramids. However, this gemstone also comes in blue, purple, yellow, orange, and pink variants.


Citrine is a variety of transparent quartz that ranges from lemon yellow to dark rich honey gold in color. The largest faceted gemstone by volume comes from the Smithsonian's 19,548 carat smoky citrine stone. Most of the citrine available in today’s market come from Brazil and Bolivia, but some are also sourced from Namibia, Tanzania, and Zambia.

For testing amethyst, tourmaline, topaz, spinels, citrine, and other common gemstones, those in the jewelry business have come to trust the Presidium Gem Tester II (PGT II), Presidium Duo Tester II (PDT II), and Presidium Gem Indicator (PGI).  

The Presidium Gem Tester II (PGT II) determines and measures precisely the thermal properties of common colored gemstones. However, it does not differentiate between natural and synthetic colored gemstones, or diamonds against moissanites. 

The Presidium Duo Tester II (PDT II) is now equipped with Presidium's Assisted Thermal Calibration (ATC) for accurate and consistent tests, the PDT II is the only comprehensive tool in the market that combines thermal conductivity and reflectivity indexes. 

The Presidium Gem Indicator (PGI) is an enhanced and more convenient handheld version of the revolutionary Presidium Gem Tester/Colored Stone Estimator. It indicates up to 31 different types of colored gems and features a color input function, allowing users to select from a range of 12 common colors, thereby achieving more accurate results. 


If you are serious about gemstones, you would want to be sure of the true value of the gems that pass through your hands. As an added layer of protection for your investment, you need the most updated instruments and technology, from a trusted brand.

Industry pioneers would have the most experience and expertise, and one such forerunner is Presidium Instruments Pte Ltd (est. 1979). Presidium is the world’s first company to launch groundbreaking gemological instruments catering specially to the jewelry industry. 

Available in more than 40 countries, Presidium products include gemstone testers that determine refractive index, UV transmittance, thermal conductivity, and/or reflectivity. Complementary products to Presidium's gemstone testers are as follows: 

The Presidium Gem Computer Gauge (PGCG) is an advanced digital computer gauge that measures gemstone dimensions, estimates gemstone weight, and identifies up to 9 different cuts. The PGCG comes with a software that lists the S.G. value, R.I. value, and hardness measurements of 133 common gemstones in the market for handy reference.

The new and improved Presidium Carat Scale – 100n (PCS-100n) measures gemstones up to 100.00 carats without the need to be calibrated each time the scale is shut off. The PCS-100n comes with a corresponding weight reference of 100.00ct/20g for calibration. This compact and portable scale can also be powered by a USB adaptor.