How To Identify Gemstones

Do You appreciate A Beautifully Colored Gem? Identify Gemstones Accurately With This Methodologic Guide

If you are a lover of colored stones, you may have built up a vast collection of natural stones of all kinds. Identifying gemstones is no easy feat without the necessary knowledge you need to investigate gem material and draw an accurate conclusion.

Our gemstone identification guide will enable you to train your eyes on what to look for in gem materials. Vague descriptions of colored stones commonly communicated to the public have led to many misconceptions as polished stones frequently have many varying characteristics that could cause people to misclassify them.

This article will not only present you with a thorough guide on gemstone identification but will also investigate the properties and characteristics of some of the most popular beautiful gemstones.

If you find that your gem identification skills could use some extra training even after reading this guide, we recommend completing the gemstone identification laboratory course provided by the Gemological Institute of America.

With adequate practice and information, you will be able to identify gemstones by mere sight. However, you may need some basic gemological equipment for the trickier stones.

Before we get started, lay out all the gem materials you would like to identify. Then, clean your stones thoroughly using a proper gem cloth. Rub each stone firmly with your clean gem cloth to remove any residual dirt or fingerprints. This will ensure the stone’s true color is apparent, and it will reflect light adequately.

For the duration of the guide, hold your stone with a pair of tweezers to avoid getting it into the oil content of your skin, which will interfere with its color integrity.

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Step 1: Observing The Basic Color, Gravity, And Transparency

What You Need:
  1. A pair of tweezers
  2. A good light source
  3. A 10x loupe

Strong magnification using a microscope is not necessary at this stage. Preferably, all observations should be made with your naked eye or, in some cases, with a 10x loupe.

You need a bright light equivalent to the intensity of the sun.

Place the stone face-up on a white or grey gem cloth, and view it from the top and the side under your fluorescent light or other daylight-equivalent. 

Investigating The Hue, Saturation, And Tone

The color of a stone is the first thing to look at when separating stones. Saturation, tone, and hue all form part of a stone’s color.

Do not shine your light directly through the stone to investigate its color. Only do this when the stone appears dark blue or green, and you need to establish whether it is black or not.

Tone

Distinguish whether your stone appears light, dark, or medium-toned, as the tone measures how dark or light a gemstone is.

Once you have identified whether your stone is dark, light, or medium, you can be more specific in its measure of tone.

Hue

Make a vague assumption about the overall hue of the stone. Which color describes it best upon first viewing.

Is it green, blue, or slightly greenish-blue? Is it a sort of reddish-orange? For an accurate reference source, keep the GIA’s color wheel open next to you and investigate which of the 31 hues in the wheel best describes your stone.

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Saturation

Make a judgment on the intensity of the color of your stone. Decide on a grade of intensity ranging from dull to extremely vivid.

To accurately judge your stone’s saturation, first, identify whether the color falls into the warm or cool color family.

Warm-colored stones will display a measure of brownness, whereas cool colors will include a few gray undertones. The more brownness the stone displays, the lower its saturation, and the less grayness present in the stone, the more vivid the saturation.

If you do not observe any brown or gray colors, your gemstone likely has a vivid saturation, but this is very rare in the most abundant minerals.

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Specific Gravity And Transparency

Assess if your stone is best described as opaque, translucent, or transparent. Further, assess the dispersion of colors that your stone exhibits: is the dispersion prominent, moderate, or relatively weak?

Translucent stones allow you to see through them to some extent while still displaying a color haze.

To investigate the gravity of the stone, you can draw an inexact but close conclusion by simply bouncing your stone in your palm to assess its heft.

Does it feel like very heavy material, or does it seem unusually light? The gravity of a gem varies widely with its crystal structure and the chemical composition of the gem material.

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Step 2: Use Light And A Loupe To Investigate Its Optical Properties

What You Need:
  1. A pen light
  2. Your 10x loupe
  3. A pair of tweezers
Optical Phenomena

Use a penlight or a concentrated equivalent to shine a bean across the stone’s surface. Look for any unique optical characteristics such as asterism, color change, sparkle, or a cat’s-eye.

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Luster

Turn your stone so the stone’s surface can reflect light and assess the extent of luster. You can assess your stone with your naked eye or using a 10x loupe. Is it waxy, dull, shiny, metallic, silky, or greasy?

If you notice any chips on your stone’s surface, describe what the surface of the area looks like. For example, did the chip form in steps, splinters, or rings? Moreover, describe the luster of the chipped area as well. The unique physical properties of a gemstone say a lot about its identity.

Step 3: Assess The Refractive Index And Your Stone’s Birefringence

What You Need:
  1. Refractive index fluid
  2. Refractometer
  3. Refractive index testing

A stone’s refractive index is one of the most clarifying aspects of identifying a gem.

The only way to do this is by using a refractometer, which takes some practice to master. Be sure to clean your stone once more before commencing this step. If your refractometer does not have a built-in light, you’ll need to shine a concentrated light down into the light port.

Whenever possible, try to close the cover of the refractometer to prevent surrounding ambient light from interfering with your results.

Following the instruction of your individual refractometer, investigate the readings through your reading lens and round the value to three decimal places.

Birefringence Testing

Birefringence testing provides valuable information that further aids gemstone identification. When determining a stone’s birefringence, you will execute a series of around six 10-degree turns until the stone is turned 180 degrees or upside down.

Envision your stone as a vertical line on a standard clock. The stone will be reaching from the 12 o’clock line down to 6 o’clock. Turning your stone clockwise, position the top edge of the stone at the 1 o’clock mark, and take another refractive index reading. Continuously move the clock to the 2 o’clock mark, then 3, 4, 5, and 6, taking a refractive index reading after each turn.

To calculate the stone’s birefringence, subtract the smallest value from the highest value and round your result to three decimal places.

If, at any point, the reading appears scattered or broken, wipe both the stone and the metal surface of the cylinder and add a new drop of RI fluid.

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Over The Limits

The refractive index fluid will always have a reading of 1.80, meaning that any gemstone with a reading above 1.80 won’t show a reading because it is over the limit. Such stones include diamonds, zircons, sphalerites, and cerussites.

Chances are, you won’t get a reading lower than 1.35. Opal’s reading of 1.37 is likely to be the lowest result you’ll find.

Step 4: Determining Whether Your Gem Has Double Or Single Refraction

What You Need:
  1. Polariscope

A polariscope will help you determine if your stone exhibits single or double refraction or if its an aggregate. Opaque and relatively opaque stones won’t provide any readings with a polariscope, so only translucent and transparent stones are suitable for this instrument.

Turn the light of the polariscope on and place your stone on the polarizer facing up on the lower glass lens.

Look at your stone through the analyzer and turn the analyzer until the area surrounding the stone appears the darkest. Looking at your stone, turn the analyzer 360 degrees until the surrounding area becomes light.

If your stone appeared dark and seemed to remain dark, it is likely single refractive. If you want to validate your results, check the stone from three different views, and if the results are constant, it is definitely a single refractive gemstone.

If your stone appears light and remains light, it is likely an aggregate. Several factors could lead to a double refractive stone appearing as an aggregate. If your stone blinks from light to dark and back again, it could be either single or double refractive with an anomalous double refractive reading.

If this is the case, you will need to repeat the process until you can establish a definitive reading. Examples of ADR stones include diamonds, opals, ambers, and synthetic spinel and garnets. If your stone appears light but exhibits a crosshatch, it is an ADR.

Tips:

If a stone has a high RI reading, you need to position it on its sides instead of face down to diminish the light that is bouncing off of its facets to gain the most accurate results.

Smaller gemstones may be more challenging to read, and you can use the magnifying lens of your refractometer found on the top of the analyzer to get a better reading.

If your gem is heavily included, try observing the most transparent parts of the stone.

If your stone has a RI of 1.73 or more and exhibits a red color, skip the step that includes the polariscope and simply use a dichroscope for this step.

If your stone is red and you found a refractive index of 1.73 or greater, abandon the polariscope and just use the dichroscope for this step.

Identify Your Gem

Now that you gathered enough information to identify your gemstone accurately, you can utilize a competent reference to look for the stone that matches your gem’s color and refractive index.

Just those two characteristics can correctly identify 95% of all gems. A good reference to use is Walter Schumann’s Gemstones of the World.

If this book leaves you with several possible results, investigate your results on the birefringence and single or double refraction to narrow it down.

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Popular Gemstones And Their Characteristics

Chrysoprase

As a specific variety of chalcedony, chrysoprase displays a yellowish-green hue. The trace amounts of nickel result in this stone’s green color.

Second only to gem silica, which is a blue chalcedony, chrysoprase is one of the most valuable chalcedony varieties. However, this gem is not broadly marketed in jewelry because of its rarity.

621px Larimar

Fancy Jasper

The Fancy Jasper gemstone exhibits splashes of white, yellow, and red colors. This dark green jasper varies widely in patterns and colors that make each gem exquisitely unique.

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Mahogany Obsidian

As a rare and valuable variety of the natural volcanic glass obsidian, the Mahony Obsidian gets its name from the brown color it holds. Some varieties are best described as black obsidian that has brown markings, whereas others have solid brown gem material. This gemstone accepts bright polish, which makes it a very popular option.

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Rutilated Quartz

A Rutilated quartz is found as clear or smoky quartz with rutile needle-like inclusions. The rutile needle inclusion varies from being only a few isolated needles to being a dense network of fibers. The needles align with the axis of the axes of this transparent quartz and are often golden in color. This smoky quartz is prized for the magnificent diversity in needle patterns.

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Morganite

Morganite is defined by its soft orange-pink color. A beautiful variety of the mineral beryl, this translucent quartz is often made to form tumbled stones and beads. In addition, Morganite is frequently set in rose gold jewelry as a faceted stone.

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Turritella

Turritella is brown, translucent quartz found in Wyoming’s Green River Formation. Its name is a bit misleading as this gem actually belongs to the genus Elimia tenera, but the christener believed it to be of the Turritella genus, and the name stuck.

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Pink Opal

The beautiful pink color of the gem material in this stone is what makes it so aesthetically pleasing to behold. The pink opal isn’t often found as tumbled stones, and they lack the play-of-color seen in the precious opal.

Pink Opal

Prasiolite

When amethyst is heated naturally or via irradiation, it forms this beautiful green quartz called Prasiolite. If the green color of the gem material is a result of human intervention, it must be disclosed before being sold. Although this gem is often referred to as the green amethyst, this name is considered misleading.

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Blue Chalcedony

Finding a gemstone with naturally blue color is very rare. That is why the Blue Chalcedony is so valuable. These exquisite blue gemstones are often found in Africa, Namibia, to be specific.

640px Blue Chalcedony (fontenelle Reservoir, Northeast Of Kemmerer, Wyoming, Usa) (32437936397)

Blue Topaz

Blue is currently the most popular color used in fashion jewelry. Because Blue Topaz is extremely rare in nature, most of the pieces we see in jewelry today is a result of heat-treated gems. Nevertheless, this stone makes for beautiful gemstone jewelry.

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Bloodstone

This gem is a dark green variety of chalcedony with a unique characteristic of having bright flashes of red. This gem has been cherished for many centuries and has served as the birthstone of March since the early 1900s.

Bloodston

Olive Opal

Olive opal is a variety of common opal. The color variations vary from greenish-yellow to yellowish-green. This opal is found as opaque as well as translucent stones, where their translucent form resembles the resinous look of a greenish amber.

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Rose Quartz

Rose quartz is found as transparent and translucent quartz with delicate pink color. This semiprecious stone accepts a very high polish and has become extremely popular for its enduring feminine air in recent years.

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Clear Quartz

Although quartz is undoubtedly one of the most abundant minerals found in the earth’s crust, finding clear quartz with little to no inclusions is very rare. This rare mineral is alternatively known as “rock crystal.” Clear quartz appears stunningly bright and captures light brilliantly.

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Blue Lace Agate

Blue Lace Agate describes the chalcedony stones that contain bands of white agate on a subtle blue agate. These bands result in a lacy effect that resembles blue lace.

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Pyrite

Pyrite, also known as fool’s gold, is the most common mineral found in the earth’s crust. It is prevalent in almost every type of rock, and its yellow color causes many people to mistake it for valuable gold. Despite not being a very rare mineral, pyrite remains unique and beautiful in its own way.

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Banded Carnelian

This reddish-brown agate often displays alternating bands of white chalcedony. These stones often have an orange to pink hue, giving them a light and cheerful appearance.

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Green Moss Agate

Moss agate is seen as a transparent to translucent chalcedony with visible inclusions. Moss agate is found in dendritic or mossy shapes and can vary in containing light to dark green inclusions.

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