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A Customer's Guide to Gemstones - TerrAdore Art Jewelry

A Customer's Guide to Gemstones


(The photos used in this article are of my own gemstones and jewelry).

Some people ask me about precious and semi-precious gems. I don't use those terms because I believe those words to be judgments, not definitions. The International Gem Society's working definition of gemstone is "Minerals that have been chosen for their beauty and durability, then cut and polished for use as human adornment...By definition, a mineral must be created inside the Earth." So lets talk rocks.


The Mohs index is a system from 1-10 that indicates the hardness of the particular type of stone, the hardest being 10 (Diamonds). The hardness of the stone is important to know for the gem cutter and gem setter. Harder stones take longer to cut and polish but give a brighter shine. Soft stones, such as Turquoise, have to be handles with more care when transforming it from rough rock to a cabochon. Soft stones, such as Opals and Turrquoise, can be damaged much more easily and are not advised for rings and bracelets for that reason. 

Transparent, Translucent, Opaque

Stones can be transparent, translucent (partly transparent) or opaque, depending on their structure. Good quality transparent stones are usually faceted *see below) to create a sparkling effect.


Faceted – faceted stones are cut on many sides to reflect and refract light which gives it a sparkle: like a diamond. Faceting takes a lot of experience, time and talent so is usually used only for transparent valuable gemstones such as the corundums (sapphires, emeralds, rubies, diamonds) but some less expensive good quality stones such as quartz (amethyst and citrine) can also be faceted. Gemstones, particularly faceted stones, have traditionally been cut by experts into standard patterned shapes: round; rectangle; square; oval; emerald; princess; trillium; rose-cut; pear, oblong, heart and marquise. Specialized intricately cut faceted stones are called "fancy" cuts.However, recently, gem cutters have been cutting facets into rough or semi-polished cabochons. This style appeals to those who prefer a more natural looking gemstone, The photos are of a customized Snowflake-cut Peridot, random faceted Garnet beads and regular oval faceted Smokey Quartz.  


Cabochon: smooth cut stone, domed (rounded) on top and flat on the back. Most stones can be made into cabochons, but particularly the opaque stones because they are not often suitable for faceting.  

Calibratedstandard sizes in standard shapes for both faceted gemstones and cabochons. Because the size is standardized, it is possible to purchase pre-formed settings for more common shapes and sizes of calibrated stones.

Freeform: stones that are either faceted or cabochons, in non-calibrated sizes and shapes. Freeform stones, require custom-made settings. Most of the cabochons I cut are freeform because I determine the shape I want to create according to the pattern, colour and quality of a particular section of the stone.

Tumbled: stones that are smoothed by a rock tumbler, but retain their basic shape. These are much more inexpensive because there is far less lapidary work involved to produce them. They are often used to make beads.

Determining the value of Gemstones

Gemstones of any value are appraised according to the 4 Cs: clarity, colour, carat, and cut.

Colour: the more saturated the colour of the gemstone, the more valuable.  For example, the most saturated coloured Amethyst in the world comes from Brazil and it is a very deep royal purple. The Amethyst from Thunder Bay here in Ontario has a variety of saturation among the crystals, from white quartz, to lavender to the dark purple. Many gemstones are treated to enhance or even change their colour. As long as the treatment does not alter the chemical composition of the stone it is considered accepted practice in the gem industry. For example, some Citrine is Amethyst that has been heat treated. Heat treatment is the most common and is considered a continuation of the  natural heating process that produced the stone. Treated gemstones are not to be confused with Lab Gemstones or Simulated Gemstones. Photos are of Brazilian Amethyst earrings, Citrine faceted pears and Prasiolite faceted trilliums.

 Carat: the size of the stone is given in carat weight and dimensions, usually metric. The larger the carat size, usually the more valuable it is. Some stones are naturally very small so the expectations for carat size are less than for other stones which are usually cut to be consistent throughout in terms of quality, colour, clarity and inclusions.

Clarity: determined by how clean and transparent the stone is. Usually, the less inclusions the better the clarity and value. There are exceptions for some gemstones, such as Emeralds, where inclusions are almost always present and indicate the authenticity of the stone. The clarity, or transparency, of Rubies for example, can be enhanced through heat treatment. 

Cut: refers to the quality of the cut and the type of cut. There are many different types of cuts and often the type of cut will also indicate the shape. For example, the emerald cut looks at first like a rectangle but is in fact an octagon because the corners have small diagonal cuts to prevent the sharp edges of a rectangle cutting the wearer or being easily damaged. Some of the best cutters in the world are in Thailand, India and Israel.

Rarity: The rarity of a stone is a strong determinant of value

 Where to find local gemstones:

Without getting too geological, rocks and minerals belong in categories according to their properties of hardness, structure etc. For example, amethyst and citrine are just different colours of quartz, like rose and clear quartz (also called rock crystal) and Prasiolite (green amethyst).   

There are many local stones here in Eastern Ontario in the Feldspar family, such as Labradorite, Perthite, Spectrolite, Amazonite, etc. but most are recognized by their schiller or irridescence. Perthite and Amazonite are found locally, particularly around Perth and Bancroft areas, whereas Labradorite is found and named after Labrador but is also available in other parts of the world. (Perthite has become quite rare because it is only found in the Perth Ontario area, so named, but there is very little left. There are so many different categories and types of gemstones and minerals It is best to have a resource to look up when working with or collecting gemstones. The following ring photos are Perthite, Amazonite and Labradorite.


When each individual stone has distinct and unique properties they are called phenomenon stones. Opals are phenomenon stones because each one has it’s own flash and colours. Stones that change colour in different light, or are fluorescent in ultra-violet light are also referred to as phenomenon stones. Some collectors and admirers (myself included) are fascinated by phenomenon stones which also increases their value.

Supply and demand, like any other commodity, has an enormous impact on the value of gemstones. Diamonds, for example, were not particularly desirable or valuable until Debeers came up with the slogan "Diamonds are Forever" and promoted Diamonds as the must have stone for engagement rings. Prior to this, engagement rings were not given or a family heirloom with any precious stone was acceptable. 

 Ethical Sourcing of Gemstones

Some stones, blood diamonds for example, are mined in ways that are considered unethical. Mining is dangerous and often exploitive of developing countries. “Ethically sourced” gemstones can be purchased from individual hand-miners, gem shows and certain companies. Before purchasing gemstones, it is important to find ethical sources that you can rely on and develop a relationship with so your stones are humanely mined and of good quality. However, just because a gemstone is identified as "ethical" doesn't mean much these days because the definition is not standardized and no governing bodies monitor the designation. I always ask what country a gem comes from and what mine, mining company or area of the country the gem originated. Then I ask where it was cut. These give me clues as to whether the gem was obtained ethically or not. I do not trust most large scale jewelry stores or companies because they buy in bulk and usually cannot identify the origin of their stones. Some smaller companies and jewelry designers specialize in ethically sourced gemstones. The movement to be more discerning and circumspect when purchasing gemstones is gaining momentum among jewelry makers and customers. 

If you are interested in the learning more about the exploitation, health, social and environmental damage caused by gemstone mining,  the short article is enlightening: When Gem Mining is a Dirty Business - A look at what to keep in mind if you want to buy precious stones with a clear conscience., by Lianna Trubowitz found in the September 9, 2011 edition of Conde Naste.

Buying Gemstones


It is hard to know whether you are getting good value for your money when you purchase gemstones, even for experts. There are a lot of good fakes and jargon terminology out there to confuse and trick buyers. Here are a few things to keep in mind that will help you make sound decisions regarding gemstone jewelry.

Start by buying from a trusted source. It is hard to know who to trust but look for credentials, like membership in the International Gem Society or guilds. Big jewelry companies do not necessarily mean they are to be trusted because they are beholden to shareholders and Executives so they don’t necessarily buy from ethical sources and many of their pieces are mass produced that lack artistry or skill.  Listen to the jeweller to see if they are truly knowledgeable or just trying to sell you something.

Ask questions, such as:

Did this gemstone come from a lapidarist or a company? Was it hand or machine cut? Which country and mine did it come from? What grade is it?

What is the hardness level of this stone? (Mohs index from 0-10, 10 is the hardest for diamonds and opals and turquoise are soft at about a 5). I do not recommend buying softer gemstones for rings and bracelets as they will inevitably get damaged.

Expensive gemstones are graded according to the 4 Cs: clarity, carat, colour and cut.) I will go into this in more detail in a subsequent newsletter but if you are curious you can find more information at:

How rare is this stone?

How should I care for this stone? Is there anything I should avoid?

Do a bit of research first. If you want to buy a piece of turquoise jewelry, for example, there are a lot of different types of turquoise out there and even more fakes. What colour turquoise do you want? Do you want it mostly solid colour or do you like it with veining in black or brown? Do you want turquoise from Arizona, Mexico, China or Africa? Do you want it to go up in value or is that not important?

My suggestion is to take a look online at all the different types of finished turquoise and find the ones you like the best. Check out the average size and price of them so you know what to look for in your price range. It seems like there is a lot of turquoise on the market but actually most of the quality American turquoise has been depleted. If you cannot find the type you want at a price you can afford, check out the vintage market because there is a lot more vintage turquoise on the market than new cuts. If you are spending more than $100 for a turquoise stone or piece of jewelry, ask for a guarantee that it is authentic. Be aware that some sellers will call a dyed Howlite or Magnesite “turquoise” and they get away with it because they are referring to the colour, not the type of gemstone. There are as many cons as there are fakes. A trusted jeweller will welcome your questions and be happy to share their knowledge.

If you are in doubt, send me a message and I will try to send you references or point you in the right direction.

 Become a Collector

Remember when you were a kid and you had a collection of rocks. Maybe you still do. Or maybe you had a tumbler - every child who loves collecting rocks should have a junior tumbler. It is very "grounding", which is how I came to lapidary work (gem cutting) and collecting.

Many beautiful stones can be found locally if you know what you are looking for. If you are interested in finding your own stones, join a lapidary club that offers field trips. Experienced local prospectors will show you where and how to obtain stones suitable for jewelry making.  Local small mines often allow the public access to their scrap piles. These contain a wealth of beautiful stones, they just aren't the ones that the company is dealing in. I like to collect stones along mountain river beds the best because the rocks have come down the mountain with the current which softens the edges and cleans the dirt. If you go right in the water, it is easier to see the ones with colour and pattern, which is what I am looking for. I have many wonderful gemstones I have collected on my travels across Canada and the United States. I have even found amazing Quartz crystals, Pyrite and Feldspars in store-bought bags of garden stones. When you see that glint in the sunshine, check it out.

So next time you pass a quarry, are hiking, or walking along a river, look down. You never know what you might find. 


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