Gemstones 101

The 4 C’s: The Reasons for Grading Gemstones

So much of how we value a gemstone comes down to looks. To put it bluntly, most people are on the hunt for the most beautiful stone they can find. While, truthfully, objectivity plays a role, there are also a few measurable ways to determine the value of a gem. The industry leans towards grading diamonds, sapphires, emeralds and more upon the 4 Cs, a method devised by the Gemological Institute of America (or GIA). This focused approach takes a look at colour, clarity, cut and carat weight.

Colour:

Colour is arguably the most important factor in grading gems. It’s very often what first draws us to any particular stone. When grading coloured stones, we first take note of the hue, or predominant colour. We also consider the tone, reflecting the lightness or darkness of a gem, and also the saturation, or purity of the colour. This is why, for instance, the potent pull of a deep-green emerald from Muzo, Colombia would be seen as a more valuable form of the mineral than the yellow-green variety found in Brazil’s Minais Gerais.

When it comes to colourless diamonds, these are rated on a scale from D (completely colourless) to Z (often marked with hints of yellow or brown).

Clarity:

The clarity of a gemstone is likewise quite important. An ideal stone will be and free from inclusions, —which are blemishes and structural flaws that could compromise the quality of a gem— and graded from eye-clean to severely included. 

That said, not all gem families are created equally, so there are three subsets to consider. Type I gems, like tourmaline and spinel, are considered virtually free of inclusions; Type II gems, like sapphire and ruby, are known to possess inclusions, but these don’t generally detract from their overall beauty; Type III gems, like the especially-included emerald, tend to be heavily flawed, with their irregularities immediately visible to the naked eye. Because of this, a crystal-clear piece of green spinel wouldn’t be as rare or valuable as a shockingly clean piece of Colombian emerald.

Cut:

Cut can greatly impact the overall beauty of a stone. While this in part refers to the shape and design of the gem, the value of a cut has more to do with well the precision of its proportions and faceting. With regards to the shape, gems can be cut into many forms, from traditional ovals to triangles and rounds. It’s the precision behind that shape that counts. A skilled cutter will know how to maximize a gem’s brightness and sparkle, and produce a symmetrical beauty that shines perfectly at any angle. A poor cut could produce windowing, where a white backing seen through the other side of the gem reduces its overall brilliance.

Carat Weight:

As a rule of thumb, bigger is better when it comes to gem stones. To be clear, though, gems are valued by weight, not physical size— One carat is roughly the same as 0.2 grams. More often than not, the higher the carat weight, the larger the price tag. Rarity also plays a big factor when it comes to valuing carat weight. Gem-quality pieces of emerald under a carat, for instance, would be significantly cheaper that a large, relatively eye-clean piece of emerald, just because it’s less likely to be found in such a hefty chunk. It stands to reason that you’re going to be paying premium for giant gems. 

Many gems can run the gamut when it comes to the 4 C’s. You might find, for instance, a Pigeon Blood ruby with excellent colour, but also plenty of internal flaws; or maybe you’ve tracked down a massive piece of watermelon tourmaline with a cut that doesn’t actually highlight it’s full, mouthwatering range of colour. You have to weigh the good against the bad. Then again, you may get lucky and find a gem that’s perfectly balanced across the 4 C’s, and ultimately just the thing for you.