Gemstone Buyers Guide

Gem Buying for the Everyday Shopper

This document has been prepared by Ashton Gems as a general introduction to gemstones. Its specific purpose is to help people with little or no background in gemology to get a quick overview of what they need to know about colored gemstones (not diamonds). Our hope is to teach you some basics and help you understand the important points before spending your money on a gem.

Keep in mind that information about gemstones could-and does-fill books. If you are interested in learning more about gemstones, we recommend any of the three listed below:

  • “Secrets of the Gem Trade” – Richard Wise
  • “The Jeweler’s Directory of Gemstones” – Judith Crowe
  • ” Gems of the World” – Cally Oldershaw

Or you can take classes, such as those offered through the Gemological Institute of America (GIA), which is the world’s foremost authority on diamonds, colored stones and pearls.

You can use the vast resources on the Internet. A few sites to include in your research are:

And last, you can always contact us!

Best regards,

Larry & Morgan Mattos, Owners
Ashton Gems
Email: [email protected]

Sections in the Buyers Guide

Types of gemstones

  • Natural Gemstones
  • Enhanced Gemstones
  • Man-Made Gemstones
  • Imitation Gemstones
  • Precious vs. Semi-Precious Gems
  • Birthstones
What to consider when buying a gemstone

  • The Four C’s: Color, Cut, Clarity and Carat
  • Where and When the Gem will be Worn
  • Gemstone Hardness and Type of Wear
Common problems when picking out a gemstone

  • Watch for Visible Natural Flaws
  • Surface Scratches and Blemishes
  • Windows and Fish Eyes
  • Jewelry and Television Don’t Mix
  • Poor Faceting

Types of Gemstones

Everyone is familiar with diamonds. They’re the “king” of gemstones, in a class by themselves, and they typically command the highest prices. Most people have heard of emeralds, rubies, opals and sapphires. But, get beyond those well-known gemstones, and familiarity begins to thin out. There are well over 100 types of gemstones, some with obscure names like sphene and tremolite-hexagonite.

For the novice, one of the most useful things to know about gemstones is probably their general class: whether they’re natural, synthetic or man-made. But there are also other ways of describing the properties of gemstones, such as whether they are enhanced, imitations, precious or semi-precious, etc. The following section provides a general introduction to some of the ways of describing and categorizing gems.

Natural Gemstones

Natural gemstones are those found in nature-that is, they occur naturally and are mined from the earth.

They are sometimes enhanced, which means they were treated in some way (such as heat) to improve their color and/or clarity. Even with enhancements, these gems are still considered natural.

Natural gemstones come in a wide range of colors-from clear diamonds and quartz all the way to black onyx. Over the centuries, gemstones have helped define the very idea of color. Consider, for example, the phrases “ruby red,” “emerald green” or “sapphire blue.”

Natural gemstones also vary widely in rarity and, therefore, in value. Scarcity can occur because the earth produced very little of a certain stone, or it may result because man has extracted large quantities of a stone. An example of the former is painite, which the Guinness Book of World Records lists as the rarest gem mineral, with only 18 known specimens. An example of the latter is morganite. Although there were numerous sources of this gem around the world, it is becoming scarce today because it is prized for its pink color and is in high demand.

Enhanced Gemstones

Gemstone cutters have been using various treatments for centuries to make gems more beautiful and attractive than they are in their natural state. Some of these treatments involve heating the gemstone. Take tanzanite. Its natural color is often a steel gray or brown that isn’t highly exciting. But, subject the stones to heat, and they turn into a beautiful blue or purple that is highly prized and often worth ten times what the same stone would sell for in its natural state.

Other gemstones-quite a long list, actually-may be heat treated, dyed or even radiated to improve the color and clear internal flaws. Examples include everything from the family of quartz crystals to topaz, sapphires, rubies and more. Many emeralds are oiled or treated with high-tech polymers to improve appearance.

Man-Made Gemstones

As technology has progressed, man has gained the ability to create gemstones in a laboratory. Man-made gems are popular today for various reasons. Producing them is far cheaper than mining, and they can be made under ideal, controlled conditions. This, in turn, means that man can produce gemstones that are virtually flawless compared to their natural counterparts. If beauty alone were the only criteria to judge a gemstone, then there would be little interest in many natural gemstones. But people still prize naturally produced stones because it’s how nature made them.

Synthetic Gemstones

The best-known synthetic gemstone material is cubic zirconia, widely known for its use in imitating diamonds. However, CZ is also used to simulate sapphires, aquamarines, topaz, peridots and others. Other materials are also used to simulate a wide variety of colored gemstones. These include corundum, a crystalline form of aluminum oxide, and man-made spinel, the magnesium aluminum member of the larger spinel group of minerals.

Imitation Gemstones

The term “imitation gemstones” refers to any stone that imitates the look or color of a natural gemstone. They can be made out of anything. As mentioned earlier, most people are familiar with cubic zirconia. Other imitation gems are made from glass or other man-made materials, and may look like an emerald, opal, ruby, sapphire, spinel, amethyst, etc. But remember, the intent with synthetic, man-made and imitation stones is always to mimic the “real thing.”

Precious vs. Semi-Precious Gems

This is a way to categorize gemstones that appears to be headed toward disuse today. The distinction of “precious” gemstones dates back the ancient Greeks, with similar distinctions also made in other cultures. Traditionally, precious gems were diamonds, sapphires, rubies and emeralds – all rare and translucent with fine color in their natural, purest state.

But the traditional distinction doesn’t necessarily reflect how we think of gemstones today, and it certainly isn’t useful in a commercial context. Many “semi-precious” stones sell for much more than what were originally considered “precious” gems. It all depends on an individual stone’s rarity, quality and the famous “four C’s” (see later section).


Birthstones are simply a way of associating the date of birth with a particular gemstone. The practice of symbolizing the birth month with a gemstone is regarded differently in different cultures. For example, the most commonly used system in English-speaking societies is based on the Gregorian calendar. But there also are birthstone systems based on the zodiac, ayurvedic traditions and other mystical origins (e.g. Tibetan).

In an effort to standardize birthstones, the Jewelers of America officially adopted in 1912 what we now know as the “modern” list. See the list on our website on the Birthstones page

Wikipedia has an interesting and comprehensive collection of birthstone lists. For more information, follow this link:

What to Consider when Buying a Gemstone

Let us begin this section by telling you what we won’t cover: how to establish the value of a gemstone. Appraising a gem is best left to an expert, and it takes years of experience, training and study to become competent in this area. If you want to know how much a gem is worth, seek out a professional appraiser with the proper credentials.

That said, we will cover the basics of what goes into determining the value of a gemstone so you understand what’s involved. Also, keep in mind that value is not merely based on price. What’s valuable to you may be based on what you think is beautiful, and beauty is subjective.

The Four C’s: Color, Cut, Clarity and Carat

Most people have at least heard of the four C’s. This system of determining the relative value of a gemstone is best known as it applies to diamonds. But these four qualities apply equally to the colored gemstones. In short, they are as follows:

1. Color – Color is typically the most important factor when establishing a gemstone’s value. It is also the most appealing visual feature of most gems. Some gems come in a variety of different colors, while others occur in narrower ranges. There is a range of preferred color for each gemstone, and the closer the stone is to this range, the more valuable it is likely to be.

There are three dimensions to color: hue, tone and saturation. Hue refers to the actual color (e.g. red, blue or green), while tone describes the lightness or darkness of the stone. Saturation pertains to the purity of the color-how much color is present-which translates into the visual intensity of the stone.

2. Cut – As gem cutters, this one is of particular interest to us because it’s where the artistry comes in. Cut refers to the workmanship, how it is faceted. It determines the shape and design of the gemstone, and has everything to do with how much light is refracted back through the stone. In turn, this makes all the difference between a plain, boring stone with little value–or a dazzling gem with luster, brilliance and enduring beauty.

For more about cut, see the following pages on this website: Cutting and Frequently Asked Questions about Gemstone Cutting

3. Clarity – Simply put, clarity refers to the absence of flaws, such as inclusions (internal flaws) or blemishes on the surface of the stone. Clarity standards vary depending on the type of gemstone, and the Gemological Institute of America has developed a clarity grading system in which all gemstones are assigned to one of three types.

But, what you don’t see in the GIA grading system is “IF” (Internally Flawless. This information/opinion was written in article by the late Jeff Gram, “Common Sense Grading System”, and is posted on his website at If you cut a gemstone that is internally flawless using 10x magnification it is grouped in the gemstones that have very minor flaws. We agree with Jeff’s opinion that this shouldn’t be done and that these gems should have their own class.

Each type of gem should be judged according to the clarity standards that apply to its class. Tanzanite, for example, should be inclusion free, while other gemstones (e.g. emeralds, sunstones) usually contain some kinds of inclusions.

Bottom line: inclusions don’t necessarily reduce the value of a stone, but there is a general relationship between clearer gems and higher value. The fewer flaws you can see with the naked eye, the higher a gemstone’s clarity and price is likely to be.

4. Carat – Carat refers to weight, which is how the size of gemstones is quantified. Not to be confused with “karat,” a measure of gold purity, the carat is a standard unit of metric weight adopted universally around the world. A carat is equal to 0.2 (1/5) grams.

As a reference point, most diamonds used in jewelry today weigh one carat or less. Colored gemstones generally run quite a bit larger than diamonds. The more valuable gemstones, such as rubies and sapphires, are generally smaller (maybe 0.5 – 3.0 carats), while gems such as tourmaline, amethyst and others can be substantially larger.

Where and When the Gem will be Worn

Now that we’ve gotten the four C’s out of the way, let’s look at what else is important when buying gemstones. Since gems are an accessory to clothing, you will want to consider what you’re going to wear WITH that gemstone and, of course, the setting in which it is mounted.

An obvious consideration is color. If you’re buying a gemstone to wear for a particular occasion, think about the color of the clothing you intend to wear with it. Will they complement or conflict with each other?

Another thought… how will that stone work with your eye, hair or even makeup color? Wearing a certain color gemstone in a bracelet may be fine, but the same color stone mounted in earrings or a necklace may not work. Give it some thought.

Lighting is a key consideration. Because gemstones refract light back through the stone, the type of lighting matters. If you plan to wear a stone outdoors in daytime, you should probably examine it outdoors in daylight to see what it really looks like under the same conditions you intend for its use. The same stone examined under artificial light (which affects gemstones differently than natural light) may look very different. No matter how and under what circumstances the gemstone will be worn, every stone should be examined in both artificial and natural light before purchasing it.

Gemstone Hardness and Type of Wear

Not all gemstones are the same when it comes to hardness. (Read about gemstone hardness on our site.) For example, amber’s hardness is around 2 on the Mohs scale of mineral hardness, while diamonds rate a full 10. The scale, named after geologist and mineralogist Friedrich Mohs, is based on the ability of one natural sample of matter to scratch another.

For this reason, you should keep in mind the type of jewelry you intend to wear when selecting the gemstone for that particular mounting. The reason is simple. Jewelry that is worn on a bracelet, watch or ring gets subjected to more impact than jewelry worn around the neck or hung from the ears. Harder gemstones will withstand the bumping and scratching, and will not show evidence of this wear as easily as softer gems.

Common Problems when Selecting a Gemstone

This is the section where we warn you how to tell, with very little further education in gemstones, what to watch out for when buying a gem. As noted earlier, there is a lot to learn, and our best advice is to get your gemstones from a qualified, professional and well-established source. This will ensure that you are not defrauded and get the most for your money.

Watch for Visible Natural Flaws

The first thing you should do is examine a potential purchase with a jeweler’s loupe or magnifying glass. As we pointed out under the Clarity section above, gems may have inclusions (sometimes called feathers). Inclusions are tiny bits of foreign debris or structural irregularities within the gemstone. Inclusions may run from the surface through the stone, or they may appear as a bubble deep inside.

Although some inclusions may not be an issue and can even enhance a stone’s beauty, 95% of them are unwanted and detract from the stone’s value. If you can see an inclusion, my advice is not to buy that stone until you learn more about it. If you really like the stone, get a second opinion. Or, if you’ve already bought it, take it to an appraiser, cutter or other gemological expert who can tell you if that inclusion adds to or detracts from the stone’s value.

Surface Scratches and Blemishes

Other problems to watch for include scratches or blemishes on the surface of the gemstone. These are rarely, if ever, desirable, and probably mean the stone has been mishandled by the cutter or was not stored or shipped properly. Don’t buy it, or if possible, return it.

Keep in mind, once a stone is scratched, it generally can’t be repaired without significantly changing the shape, size or cut. The reason is that, to get rid of a surface blemish, the stone must be re-cut and polished again, which inevitably some of ALL surfaces must be removed in order to make the facets (cut surfaces) uniform. If a gem dealer tries to convince you that it is nothing or that he can simply polish it out, it’s probably not true.

Windows and “Fish Eyes”

Windows are noticeable areas on the crown (top surface) of a gemstone where light does not reflect back to your eye. In other words, you can essentially “see through” the gem. You can test this for yourself by moving the stone over a piece of paper with writing on it. If you can see the letters through the stone, it has a window. This means the stone was not properly cut, and light is going through the gem and not reflecting back at you (a loss in brilliance).

“Fish eyes” are another word for windows. In a mounted stone when you can’t do the paper test described above, the “fish eye” will appear as a dark, perhaps black spot in the stone as you look at the pavilion. Avoid purchasing this stone or, if possible, send it back and get a refund.

Jewelry and Television Don’t Mix

Have you ever watched any of the TV jewelry channels? One night, we watched a jewelry sales show. It was amazing how they were able to sell such beautiful gems and jewelry at such low prices! The “deals” were unbelievable. One item was a “rare, real, man-made” gemstone for $29.99 mounted in a ring setting.

Gemstones are either man-made or real, but not both. Many people we know have purchased rings, earrings and necklaces from various jewelry channels over the years and were, more often than not, disappointed at the quality.

Some of the problems they encountered were:

  • The gemstone was a lot smaller than it appeared on TV.
  • The color was either lighter or darker than they had hoped.
  • The gemstone was badly cut or scratched.
  • The gemstone fell out of the setting due to loose mounting.

If it sounds too good to be true, it probably is.

Poor Faceting

As we explained earlier, the cut (one of the four C’s) generally makes the difference between an ordinary stone and a stunning work of art. While you may or may not notice the difference yourself, many of the stones cut overseas are faceted factory-style in mass quantities, perhaps by cutters with poor equipment and little or no real training. They are paid based on quantity-not quality, and their work reflects this.

This can result in issues such as uneven facets, irregularly shaped stones and a lackluster finished product. The best advice we can give you is to do business with a source you know and trust so your gmstone not only looks better, but holds its value and maybe even appreciates over time.

Our Offer to You

If you have a gemstone you’d like us to cut or re-cut, we will examine it at no charge and provide a free estimate. Or, if you would like us to find and cut a particular gemstone, we will provide a free estimate for that service as well. All our work is backed by a complete satisfaction guarantee and 15-day return policy.

We provide consumers, jewelers and jewelry designers with outstanding customer service and superior-quality gem cutting.

Please Contact Us for more information.

Larry and Morgan Mattos
Ashton Gems
[email protected]