Inclusions in Gemology - General considerations

In gemology, the study of inclusions is a very important part of everyday practical work and scientific investigations. A10x triplet loupe is a basic tool always present in a gemologist’s bag, and a microscope is usually the first tool used in a gemological laboratory for gem identification.

Inclusions in gems are important in different ways, corresponding to different approaches for their study. Let’s consider separately three roles of inclusions in gemstones:

  • inclusions as a flaw for gem’s clarity
  • inclusions as a source of information
  • inclusions as necessary or beneficial component for some gems


In general, different characteristics observed inside a gem, such as inclusions of different types, uneven color distribution, graining, fissures and fractures, are usually described in gemology as “internal characteristics”. Different inclusion types are described in detail in another special section. In this part of our website, other important internal characteristics, such as graining, color distribution, fissures and fractures are considered, together with some special effects caused by inclusions in gems, such as chatoyancy, asterism and aventurescence.

Gemological loupe and microscope, basic tools for gem identification and grading.


Inclusions as a flaw for gem’s clarity

For any naturally formed mineral, it is always much harder to find transparent and clean crystals than those full of inclusions. Abundant inclusions can turn a potentially valuable material into something that is totally unsuitable for polishing and that lacks gemological value. By extension, a term “gem quality” or “gemmy” is frequently used by mineral collectors for transparent crystals, even for soft minerals that can’t be used as gems.

Gem materials are scarce in nature, and rarity is one of the factors that make a certain gem more or less valuable. Once polished, gems that have fewer inclusions are scarcer than those with more inclusions visible to the naked eye or by loupe, giving an additional rarity and value factor to clean gems.

Examples of diamonds of different clarity grades, from left to right, IF, VS, SI and I.


Since inclusions are natural obstacles for the passage of light, they negatively affect the brilliance and therefore the beauty of a faceted gem. For all these reasons, the general rule for gem quality with regards to inclusions is “the fewer – the better”. One of the tasks of a gemologist or gem appraiser consists on giving a certain grade of clarity to a gem for its valuation.

For colored gemstones, clarity is graded by naked eye, so inclusions visible only under magnification don’t affect clarity. In contrast, in diamonds even tiniest pinpoints visible only with 10x loupe can lower the clarity grade and hence the value of the stone.

Small dark garnet inclusion in diamond, located in the worst possible position, multiplied all through the stone, in pavilion and crown facets. The only true inclusion is observed directly in the middle of the table; all others are reflections of the same crystal. Field of view 2.8 mm.


With regards to clarity grading, not only solid and fluid inclusions matter. Despite them not being inclusions in the proper sense, different kinds of internal flaws such as fissures, fractures and cavities are also taken into account. They are considered more in detail in the following section.

Of course, negative effect on clarity of gems is an important bad side of inclusions, but let’s be positive and concentrate on their very beneficial roles for gems and gemology!


Inclusions as a source of information

Sometimes, simple observation of inclusions with a loupe can be enough to identify a gem, with no need for additional analyses. Inclusions are crucial for distinguishing between natural gems and their synthetic analogues, and also for detecting treatments applied to the gemstones. Moreover, study of inclusions can provide substantial information for determination of geographical origin of a certain gem.

All this important information transforms “flaws” inside a gem into a kind of treasure for gemologists. Combined with the beauty of the internal microworld of gems, it is not a surprise that many gemologists get passionate about inclusions and start to collect most interesting and nice samples!

Dendritic agate from Brazil. Field of view 5.5 mm.


Inclusions as necessary or beneficial component for some gems

Importance of inclusions is especially remarkable for those gems that simply wouldn’t exist without inclusions, or those that increase their quality thanks to them. Some examples of such cases are presented below.

  • Inclusions are responsible for providing color to some gems. Minerals that would be colorless in a chemically pure state, colored by chemical impurities, defects in their structure or inclusions of other minerals, are called allochromatic (“other colored”), in contrast to idiochromatic minerals with their proper coloration. Classic examples of gems colored by inclusions are: jaspers, agates and chalcedonies (with wide variety of coloring inclusions), rose quartz (tiny dumortierite needles), red quartz (hematite), milky quartz (fluid inclusions), among others. More recently, many new commercial names of quartz with inclusions have appeared, such as “Paraiba quartz” (gilalite), “pink fire quartz” (covellite), “sunset quartz” (unknown inclusions), etc.


So called “Paraiba quartz”, colored by gilalite inclusions. Field of view 11 mm.


  • Inclusions are very important as a cause of special optical phenomena, creating different gem varieties. Such are the examples of asterism, chatoyancy and aventurescence, caused by inclusions. These phenomena are described more in detail in corresponding sections below.


Chatoyancy in orthoclase (moonstone) form India. Field of view 20 mm.


  • Some gem varieties are specially designated for gems with certain kinds of inclusions, visible by the naked eye and providing them a special aesthetic value, compared to the same mineral without inclusions. Common examples are rutilated quartz or topaz, moss and dendritic agate, chiastolite and “trapiche” gems.


Rutilated quartz from Brazil. Field of view 20 mm.


Moss agate from India. Field of view 22 mm.


  • Finally, in some very particular cases, tiny submicroscopic inclusions can produce visual increasing of color saturation in gems. Such is the case for the famous “velvet blue” color of some sapphires, especially those from the Kashmir region, but also known in other origins (R. Hughes, 2017, in press). Also, a very slight lack of transparence associated with some very fine color emeralds from Colombia, known as “gota de aceite” (oil drop), probably has the same effect on color saturation.



Magnificent velvet blue sapphire from Madagascar, photographied with lightly colored rough sapphire crystals from Kashmir. Photo: Wimon Manorotkul/Lotus Gemology.