Published January 2022  •  Updated March 2023  •  Read Time: 6 minutes

Have you ever wondered how crystal quality is determined? You may have seen crystals listed as “A” or “A+” or even “AAA.” Perhaps you’ve noticed that these kinds of grades are listed on the product pages here at Moonrise Crystals.  They might seem official, but crystal quality is actually quite subjective!  There is no universal standard for stone grading except in the case of Diamonds, which are famously graded according to the 4Cs of color, clarity, cut, and carat weight.  All other stones, both precious and semi-precious, are graded by hand according to the professional opinion of the grader.  Learn more about how crystal quality is determined from the most precious diamonds to common tumbled stones.

Crystal Quality crystal quality

How Precious Stones are Graded

Diamond Grades

Diamond is the only stone that has strict universal grading standards.  All other precious and semi-precious stones are graded more casually, taking their cues from diamonds.  Fine gemstones like Sapphire, Emerald, and Ruby are typically graded by professional gemologists.  Some gemologists also deal with the many other stones sold as healing crystals. The majority of industry experts who grade stones due so according to their own personal experience and preference.

The grading system for diamonds was developed in the 1950s by the GIA (Gemological Institute of America).  Quality is judged by the 4Cs – Color, Clarity, Cut, and Carat weight.  Each factor is rated independently and the final value of the diamond is determined by the combination.  The rarer the combination, the higher the price.  The most precious diamonds are either usually completely colorless, although a rare vivid color such as blue, such as the Hope Diamond, is also very valuable.  The most expensive diamonds are also flawlessly clear, beautifully cut, and large.

Diamonds are graded on a color scale of D-Z.  Interestingly there is no such thing as an “A Grade” Diamond!  While most people think of diamonds as a colorless gem used in expensive jewelry, only a small percentage of diamonds meet the strict quality standards for fine gemstones.  Diamonds that are N-Z grade are typically used industrially, for example in diamond-tipped tools.  These diamonds don’t look very remarkable, but they have an exceptional hardness that makes them very useful.

Diamond Colors Grade
Colorless D-F
Nearly Colorless G-J
Faint Color K-M
Very Light to Light Color N-Z

Of the 4cs, Color and Clarity are the most strictly regulated, while Carat weight is the simplest to calculate.  These three factors are all gifts from Mother Nature. By contrast, Cut is due entirely to the work of skilled artisans.  A high-quality cut creates the facets which reflect light in a dazzling display.  Round diamonds are the standard shape, everything else is known as a “fancy cut.”  The brighter the dazzle, the more expensive the diamond.

Diamond Clarity Grade
Flawless 1-2
Very Very Slightly Included 3-4
Very Slightly Included 5-6
Slightly Included 7-8
Included 9-11

Other Precious Gems

Colored Stones used in fine jewelry are also judged by the 4Cs.  Cut and Carat weight are the same as in Diamonds, but Color and Clarity are much more subjective!  For one thing, color interpretation is unique to each person, and lighting can also dramatically change how a color appears.  To further complicate the matter, many stones have multiple colors, such as blue-green, or reddish-purple.  In a small company, a single person might be tasked with judging each stone’s color and deciding how to characterize it.  In larger companies, two or more people may have to independently judge each stone.  While care is taken for accuracy, it is still a subjective judgement.  Color is based on hue, tone, and saturation.  The hue is the basic color, for example “blue,” while tone is how light or dark it is.  Saturation is the most important factor; this is how intense the color appears.  The best quality colored stones are called “Vivid,” the next best saturation is “Intense.”  For Clarity in diamonds, the goal is typically to be “flawless” with no inclusions whatsoever.  For colored stones, the goal is to be “eye clean” since inclusions are what give these stones their color.

An example of a particularly exquisite colored stone is “The Titan’s Eye” owned by the Natural Sapphire Company and available for just under 3 million dollars.  This ultra-rare natural Blue Sapphire is one of the largest in the world at 69 carat weight.  Its color is “intense,” its clarity is “eye-clean,” and its cut is an oval.

How Semi-Precious Stones are Graded

What is a Semi-Precious Stone?

Only four gems, Diamond, Emerald, Sapphire, and Ruby are considered “Precious Gems.”  Any other pretty gem can be considered semi-precious, including stones like Amethyst, Jade, Moonstone, and Tourmaline.  Some of these semi-precious stones can be expensive like Tanzanite, Topaz, or Turquoise.  Others can be relatively inexpensive such as Blue Lace Agate, Gold Tigers Eye, and Red Jasper.  There is no scientific reason for a stone to be considered precious vs semi-precious.  It is a matter of economics and perceived value.  For example, the mineral Beryl come in a variety of colors.  If the Beryl is green, it’s a precious Emerald.  If it’s blue, a semi-precious Aquamarine, if it’s pink a semi-precious Morganite.  Red Beryl is actually the rarest variety and is found in only in the Wah Wah Mountains of Utah, USA.  After factoring for crystal quality, a Red Beryl is worth more than an Emerald, nevertheless, a Red Beryl is considered semi-precious.

How are Tumbled Stones Graded?

Healing Crystals include both precious and semi-precious stones.  The crystal quality can range from the highest jewelry grade to cheap tumbled pebbles, and everything in between.  Most tumbled stone producers only produce one grade of stone, which is whatever quality the factory owner considers to be acceptable.  The world’s leading producer of tumbled stones divides their stock into two categories.  Unsorted (sometimes called “D” or “C” quality) and Hand-sorted.  Hand-sorted tumbled stones may be further sorted into B, B+, A-, A, A+, AA, AA+, and AAA.

At Moonrise Crystals, grading may be partially determined by the supplier, if they grade their stones, and partially by Julie after she has hand-sorted the inventory.  In some cases, the supplier does not grade their stones, in which case crystal quality is entirely determined by Julie based on almost 15 years of professional experience.

Moonrise Crystals only sells crystals that are categorized as A, AA, and AAA.
Grading is determinized by a combination of factors:


Stones with a vivid and pure color receive higher grades. Ideally, the color should look attractive in all lighting conditions. If the stone has colorful patterns, they should be distinctive rather than muddied.


Transparent stones are typically graded higher than opaque stones. Clarity is eye-grade and can be assessed without magnification. For dark-colored stones, the transparency may only be observed when the stone is backlit.

Iridescence & Prisms

Stones that have a strong iridescence receive higher grades. While clarity is valued, attractive inclusions that create rainbow prisms may also contribute to a higher grade.


In general, polished stones should be smooth. But depending on the hardness of the stone, the matrix it grew in, and the type of polishing it received, the stone may have scratches or cavities.  Sometimes these natural caves add to the beauty of a stone.

AAA Color

Rhodonite Brazil rhodonite gem

AAA Clarity

Himalayan Gold Quartz himalayan gold quartz

AAA Iridescence

Rainbow Obsidian Galaxy rainbow obsidian galaxy

Treated Stones

What are Artificial Treatments?

Fully natural stones will always be graded higher than treated or manmade stones. Brighter colors and iridescence can be artificially produced by irradiation, heat-treatments, dye and other factory processes.

Dyed Stones

Some stones are naturally porous and can be easily dyed a bright and vibrant color.  This is not a new development, crystals have been dyed since the Roman Empire.  Agate is the stone most likely to be dyed, but Calcite is also sometimes dyed.

Heat Treated Stones

The color of stones is due to the presence of trace inclusions.  In some cases, the mineral inclusion will always create the same color, for example Chromite consistently gives a vivid green color as seen in Green Aventurine.  But other inclusions can change color depending on temperature.  This is most notable for Iron inclusions, which can turn red, purple, yellow, or green depending on the temperature!

In some cases, a lower-quality crystal will be artificially heated to change its color.  Lower-quality Amethyst is sometimes heat-treated to become a vibrant yellow Citrine or a pale green Prasiolite.

Man-Made Crystals

Occasionally a stone is man-made.  One of the oldest examples is Goldstone, which is a very glittery glass that has been produced since the 17th century.  More recently there’s been a rise in stones with names like “Aqua Aura” or “Blue Obsidian.”  Many of these stones are a man-made glass.  Others are natural stones, typically quartz, that has been artificially treated in some way.  For example, Aqua Aura is created when Quartz is heated in a vacuum chamber along with a gold vapor.  The gold atoms settle on to the Quartz and coat the surface a lovely iridescent blue.