Diamond Education - OMI Jewelry



last updated: may 2024



diamond clarity

carat weight

Diamond Anatomy

Below is an explanation of the major parts of a diamond. When considering diamond anatomy, the three most important components are diameter, table, and depth. This is because the ratio of the table to the diameter, and the depth to diameter, figure prominently in determining a diamond's cut grade.


While understanding a diamond's anatomy can be helpful, it should not supersede the importance of or be confused with cut grade. The various parts of a diamond and how well they are cut are included as part of a diamond's cut grade.


Diameter:The width of the diamond as measured through the girdle.


Table: The largest facet of a gemstone.


Crown:The top portion of a diamond extending from the girdle to the table.


Girdle: The intersection of the crown and pavilion, which defines the perimeter of the diamond. While generally a minor consideration, it is recommended to avoid girdles graded either extremely thin, which makes diamonds more susceptible to chipping, or extremely thick, which puts too much weight in the middle of the diamond, causing it to look smaller than diamonds of similar weight.


Pavilion:The bottom portion of a diamond, extending from the girdle to the culet.


Culet:The facet at the tip of a gemstone. The preferred culet is not visible with the unaided eye (graded "none" or "small").


Depth: The height of a gemstone measured from the culet to the table.

diamond shape

OMI Jewelry has a large variety of loose diamonds, varying in shapes, size, and other characteristics, not listed on the website. All diamonds, if not already GIA certified, can be certified by GIA upon request. GIA is one of the most prominent laboratories to certify loose diamonds.


Loose diamonds can be purchased separately.


All diamonds are different, even ones that are the same shape. Therefore, each diamond cut has different characteristics, which are unique to its shape, that determine the quality for each shape.

Round Cut Diamond

Round diamonds are the most popular diamonds, as well as the most coveted. In addition to being the most popular and researched shape, a round diamond will typically give you more flexibility in terms of balancing cut, color, and clarity grades while still getting the fire and brilliance you want. The round diamond consists of 58 facets, and can sometimes give off a larger look than it actually is. The round diamond is truly the classiest and timeless shape in diamonds.


Hearts & Arrows In A Round Diamond:  Requests for hearts and arrows in a round diamond have increased in recent years. What does hearts and arrows mean? A diamond that has the top facet or "table facet" exactly perpendicular to the bottom of the diamond or "pavilion" and has its other facets precisely aligned with excellent symmetry, may show patterns that look like arrows from the top and hearts from the bottom. Generally it will need to be viewed loose under a gem scope to see the pattern very well.

Princess Cut Diamond

The princess cut diamond is the second most popular diamond. The face-up shape, or the top, of the princess cut is square or rectangular and the profile or side-on shape is similar to that of an inverted pyramid with four beveled sides. Princess diamonds can vary greatly on how square or rectangular they are cut. For ideal cut proportions, please visit the “Cut” section of the Education tab. The princess cut diamond can also be referred to as the “square modified brilliant”.


Choosing the right shape for princess cut diamonds can sometimes be a challenge, but here are some tips; if you are attracted to a princess diamond shape that is more square than rectangle, then look for length-to-width ratios between 1 MM and 1.05 MM. Alternatively, if you prefer, or are attracted to more of a rectangular shape, you’re looking for length-to-width ratios greater than 1.10 MM.


In relation to the price, a princess cut diamond is usually slightly cheaper than a round cut diamond of the same carat weight because it retains about 80% of the rough diamond, as opposed to the round brilliant which retains only about 50% of the rough. The ability to retain more crystal weight makes this shape popular among diamond cutters.

Emerald Cut Diamond

The emerald cut diamond falls into the category of fancy cut diamonds. The emerald diamond is unique in its nature because of its pavilion. The pavilion is the bottom portion of the diamond, and it extends from the girdle to the culet. The pavilion in the emerald diamond is cut with rectangular facets, which creates an interesting optical appearance. Due to its larger open table, the emerald diamond’s rectangular shape showcases the diamonds clarity. Like the princess cut diamond, the emerald cut diamond varies in how rectangular in shape it is cut.


If you are in the market for a classic emerald cut shape, here are the ratios to abide by: look for the ratio between 1.30 MM and 1.40 MM.

Asscher Cut Diamond

The Asscher cut diamond, also falling in the category of fancy cut diamonds, was created by the Royal Asscher family, hence the name. The beautiful Asscher cut originally was created to have 58 facets, but was later reinvented to have an extra break in the diamond's pavilion giving it an astounding 74 facets. The Asscher cut diamond can be viewed as similar to the emerald cut diamond, with the difference being that the Asscher has a squarer cut. The Asscher cut diamond is famously known for its superior light performance when compared to other step cut diamonds.


The ideal cut for the Asscher cut diamond has a length to width ratio between 1.00 MM and 1.05 MM.

Marquise Cut Diamond

The only diamond that actually represents the shape of a diamond, the marquise cut diamond truly maximizes the carat weight you are getting, providing you with a diamond that looks a lot larger than it actually is. The marquise cut diamond is elliptical in shape with pointed ends. Like many other diamonds that provide an optical illusion, the marquise cut diamond creates an illusion of longer and leaner fingers. Marquise cut diamonds, because of their cut, are more prone to showing more color and inclusions in comparison to other cut diamonds. An important note for marquise cut diamonds, make sure to protect the points because they can sometimes chip.


The ideal cut for the marquise cut diamond is a length to width ratio between 1.75 MM and 2.25 MM.

Oval Cut Diamond

Oval cut diamonds are a cross between the marquise diamond and the brilliant round cut diamond. Like the marquise cut diamond, the oval cut diamond is elliptical in shape, and helps to elongate the fingers. Like the round cut diamond, the oval cut diamond has similar brilliance that shines through. Well-proportioned oval cuts should have a minimal bow tie effect.  A bow tie is a dark area across the center width of many fancy shapes—a result of varying pavilion angles.  Bow ties show as light return that is blocked by the head of the viewer.


The ideal cut for an oval cut diamond is a length-to-width ratio between 1.33 MM and 1.66 MM.

Radiant Cut Diamond

The radiant cut diamond is very similar to the princess cut, square modified brilliant, diamond. They are square or rectangular mixed cuts with angled corners. The radiant was created to be an alternative to an emerald cut diamond. Radiant cut diamonds are also known as “Cut Cornered Modified Brilliant”. The nature of a radiant cut diamond helps with the concentration of color.


If you are looking for a radiant cut diamond shape that has a squarer facade, then you should be looking for length-to-width ratios between 1.0 MM and 1.05 MM. Alternatively, if you desire a radiant cut diamond with more of a rectangular shape, then you should be looking for length-to-width ratios greater than 1.10 MM.

Pear Cut Diamond

Pear cut diamonds are well known for their classy and brilliant elegance. The pear cut diamond is a mix between the marquise cut diamond and an oval cut diamond. The pear cut diamond is also referred to as a tear drop cut because of its single point and rounded edge. Because of it similarity to the oval and marquise cut diamond, the pear cut diamond is also known to elongate the fingers. The pointed end of the pear cut diamond should be protected to prevent possible chipping. Pear cuts can sometimes have a prominent bow tie area.


For the most traditional pear-shaped diamond, look for a length-to-width ratio between 1.45 MM and 1.75 MM.

Heart Cut Diamond

The heart diamond can be seen as taking a step further to symbolize your love. Heart cut diamonds are brilliant cuts with curved lobes that stem from the center cleft. Color can be more visible in hearts, especially in the lobe areas.  Hearts may also show a bow tie. Fancy shapes like ovals, marquises, hearts, and pears will have bow ties of varying degrees, and it is best to avoid excessively deep or shallow stones.  Look for hearts with balanced and symmetrical proportions.  A defined cleft with even lobes and a sharp point are generally preferred.


If you are looking for an ideal cut diamond, then you should be looking for a length to width ratio between 0.90 MM and 1.10 MM.

Cushion Cut Diamond

Cushion cut diamonds definitely stand out because of their truly unique cut. An alternative name for a cushion cut is pillow cut. This is because of its rounded corners and larger facets, which ultimately helps to increase the diamond's brilliance and shine. The larger facets showcase the diamond's clarity very well. Cushion cut diamonds are available in different shaped cuts, ranging from a squarer facade to a more rectangular one, depending on your preference or taste.


The ideal cut measurement for a cushion cut diamond for a squarer cushion, a length to width ratio between 1.0 MM and 1.05 MM. For a more rectangular cushion cut diamond, the ideal measurement is a length to width ratio greater than 1.15 MM.


The cut of a diamond — its roundness, its depth and width, the uniformity of the facets — all determine a diamond's brilliance. Many gemologists consider cut the most important diamond characteristic because even if a diamond has perfect color and clarity, a diamond with a poor cut will have dulled brilliance.


The width and depth have the greatest effect on how light travels within the diamond, and how it exits in the form of brilliance.


Too Shallow: Light is lost out of the bottom causing the diamond to lose brilliance.


Too Deep: Light escapes out of the sides causing the diamond to appear dark and dull.


Polish and symmetry are two important aspects of the cutting process. The polish grade describes the smoothness of the diamond's facets, and the symmetry grade refers to alignment of the facets. With poor polish, the surface of a facet can be dulled, and may create blurred or dulled sparkle. With poor symmetry, light can be misdirected as it enters and exits the diamond.


The polish and symmetry grades are clearly listed in each diamond detail page and within the AGSL or GIA diamond grading report. For the most beautiful diamond, look for a symmetry grade of ideal (ID), excellent (EX), very good (VG), or good (G) for an AGSL graded diamond, and excellent (EX), very good (VG), or good (G) for a GIA graded diamond. Avoid diamonds with symmetry grades of fair (F) or poor (P), as the alignment of their facets may misdirect light so severely that it affects the brilliance of the diamond.


Diamond measurements are calculated and applied to a cut grading scale that makes it easy to understand how well each reflect light.


For the best value in a brilliant diamond, choose a diamond with a cut grade of good or very good, and polish and symmetry grades of very good or good.


In an ideal or very-good cut diamond with very good or good polish and symmetry, consider less expensive grades of color and clarity — look for a diamond with G or H color and SI1 or SI2 clarity.


Acting as a prism, a diamond can divide light into a spectrum of colors and reflect this light as colorful flashes called fire. Just as when looking through colored glass, color in a diamond will act as a filter, and will diminish the spectrum of color emitted. The less color in a diamond, the more colorful the fire, and the better the color grade.


D: Absolutely colorless. The highest color grade, which is extremely rare.

E: Colorless. Only minute traces of color can be detected by an expert gemologist. A rare diamond.


F: Colorless. Slight color detected by an expert gemologist, but still considered a "colorless" grade. A high-quality diamond.


G-H:Near-colorless. Color noticeable when compared to diamonds of better grades, but these grades offer excellent value.


I-J:Near-colorless. Color slightly detectable. An excellent value.


K-M: Not Available


N-Z: Not Available


Some people seek diamonds that produce this unique effect, while others definitely avoid it. The visible effects of fluorescence grades of faint, inert, negligible, and medium, can only be detected by a trained gemologist. A fluorescence grade of strong or very strong can make a diamond with a near-colorless grade look even whiter yet in some instances give the diamond a slight hazy or oily appearance. Diamonds with a strong or very strong fluorescence are priced slightly lower than other diamonds.

what color grade is best?

For the purist, look for a colorless diamond with a grade of D-F and a fluorescence rating of faint, inert, none, or negligible.


For an excellent value in a diamond with no noticeable color to the unaided eye, look for a near-colorless grade of G-I, and a fluorescence grade of medium or strong blue.


Or, if you'd rather not compromise on color but would like to stay on budget, choose a diamond with a good cut, SI1–SI2 clarity, and consider going with a strong fluorescence. It will still be beautiful to the unaided eye and you may prefer the unique effect of a strong fluorescence.

diamond clarity

Diamonds that are absolutely clear are the most sought-after and therefore the most expensive. However, many diamonds have inclusions — scratches, trace minerals or other tiny characteristics that can detract from the pure beauty of the diamond. GIA and EGL use a detailed system of rules and standards to summarize the number, location, size, and type of inclusions present in a diamond.


FL, IF Diamonds:Flawless: No internal or external flaws. Internally Flawless: No internal flaws. Very rare and beautiful diamonds.


VVS1, VVS2 Diamonds: Very, Very Slightly Included: Very difficult to see inclusions under 10x magnification. An excellent quality diamond.


VS1, VS2 Diamonds:Very Slightly Included: Inclusions are not typically visible to the unaided eye. Less expensive than the VVS1 or VVS2 grades.


SI1, SI2 Diamonds: Slightly Included: Inclusions are visible under 10x magnification, and may be visible with the unaided eye. A good diamond value.


I1, I2, I3 Diamonds:Included: We do not carry diamonds of I-grade clarity.


We recommend that you select an "eye-clean" diamond — one that has no inclusions visible to the unaided eye. An excellent value, diamonds of this clarity are much less expensive than IF- or FL-grade diamonds and typically do not contain visible inclusions that detract from the beauty of the diamond. If you're considering an SI grade diamond, call to speak to a diamond and jewelry consultant who will review the diamond to ensure the inclusions are not visible with the unaided eye. But, if you'd rather not compromise on clarity yet are budget conscious, choose a diamond with a good cut and G or H color.

carat weight

Once you've determined what cut, color, and clarity grade you're looking for in a diamond, it's easy to determine the carat weight of diamond that will fit within your budget.


When diamonds are mined, large gems are discovered much less frequently than smaller ones, which makes large diamonds much more valuable. In fact, diamond prices rise exponentially with carat weight. So, a 2-carat diamond of a given quality is always worth more than two 1-carat diamonds of the same quality.


To choose the best carat weight of diamond, consider style, finger size, setting size, and budget.


If you have a set budget, explore all your options and you'll find that there is a wide range of diamond carat weights and qualities available to you.


If your recipient is very active or not used to wearing jewelry, she may find herself bumping or nicking her new ring. Consider a smaller size diamond or a setting that protects a larger diamond from getting knocked against doors and counters.


Also keep in mind that the smaller the finger, the larger a diamond will appear. A 1½-carat diamond solitaire looks much larger on a size 4 finger than a size 8 finger.


Finally, if a large carat weight is important to you, yet you're working within a budget, consider a diamond with a good cut, SI1–SI2 clarity, and an I or J color grade.