Inclusions in Gemstones: Types, Origins and What They Reveal
An inclusion is a foreign body (crystal, liquid, gas) or a fracture trapped inside a crystal. Rutile, chlorite, bubbles, fissures: each one tells the story of how the stone formed.
Key points
| Definition | A solid, liquid or gaseous foreign body trapped inside a crystal |
|---|---|
| Origin | Before, during or after the growth of the crystal |
| Examples | Rutile in quartz, chlorite (lodolite), water bubble (enhydro), “garden” in emerald |
| Use | Identifying the species, spotting synthetics and imitations, sometimes suggesting the origin |
| Tool | 10x magnifying loupe |
| Diamond clarity | 11 grades on the GIA scale, from FL to I3 |
What is called an inclusion
An inclusion is anything found inside a crystal without being part of it: another mineral, a droplet of liquid, a gas bubble, or even a fracture or a twinning plane. Gemmologists also speak of “internal characteristics”. They are a normal result of a crystal growing in a natural environment that contains other minerals, fluids and impurities.
An inclusion is not always a flaw. In jewellery stones, it can lower the value if it interferes with transparency. But in collector and decorative stones, it often is the point of the piece: a quartz with golden needles, a crystal with a “garden” of chlorite, a moving drop of water.
Depending on when they were trapped
| Type | When? | Example |
|---|---|---|
| Protogenetic | The enclosed material existed before the host crystal | Small tourmaline or rutile crystals enveloped by quartz |
| Syngenetic | They grew at the same time | Growth ghosts, some chlorite gardens |
| Epigenetic | Appeared after the crystal had grown | Healed fractures, iron oxide deposits along breaks |
This distinction is useful to specialists, but it has a practical consequence: from these inclusions, one can deduce the order in which the minerals formed.
Solids, liquids, gases
- Solid inclusions. Rutile in golden needles (rutilated quartz, see rutilated quartz), tourmaline in black sticks (tourmaline quartz), green chlorite in small clusters (garden quartz), red hematite in flakes (hematoid quartz), the green mica of aventurine, pyrite crystals. In phantom quartz, layers of dust mark former growth surfaces (phantom quartz).
- Liquid inclusions. Droplets of salt water or carbon dioxide, often invisible to the naked eye. Milky quartz contains billions of them. An “enhydro” is a cavity holding enough liquid for a bubble to move when the stone is tilted.
- Gas inclusions. Bubbles, sometimes round, sometimes elongated.
- Multiphase inclusions. In Colombian emerald, one typically finds cavities containing a liquid, a gas bubble and a small cubic crystal of halite: these are called “three-phase” inclusions.
The “garden” of an emerald refers to all its fissures and inclusions: a beautiful, nearly flawless emerald is exceptionally rare. See emerald.
What inclusions reveal
| What you see under a loupe | What it suggests |
|---|---|
| Round, isolated bubbles, sometimes in a string | Glass or a synthetic stone made by melting |
| Curved growth striations | Flame-fused synthetic corundum (Verneuil method) |
| Fine needles crossing at 60° (“silk”) | Rutile in natural corundum: ruby, sapphire |
| Veils or irregular droplets | Growth fluids; possible synthesis in solution |
| Three-phase cavities | Natural emerald from certain deposits, including Colombia |
| Iridescent fissures, feathers | Natural fractures |
| Insect in resin | Amber, copal… or a fake: a recent insect may have been added to modern resin |
None of these observations is proof on its own. They guide a gemmologist, who completes the picture with other tests. For amber and its imitations, see how to recognise real amber.
Inclusions and treatments
Inclusions and fractures are also what some treatments try to reduce:
- the heating of sapphires can partly dissolve rutile needles;
- the filling of emerald fractures with oil or resin is common; filling of rubies with a lead-rich glass has grown considerably since the 2000s;
- for diamond, a laser can drill a path to a dark inclusion, after which an acid dissolves it or makes it less visible.
These treatments are documented by laboratories. They must be disclosed to the buyer. See our commitments and certificates.
Clarity: the diamond scale
For diamonds, the American laboratory GIA uses a clarity scale of 11 grades, assessed at 10x magnification: FL (flawless), IF (internally flawless), VVS1, VVS2, VS1, VS2, SI1, SI2, I1, I2, I3. The further down the scale, the more visible the inclusions. For coloured stones, expectations are different: an aquamarine is expected to be almost clear, but a heavily included emerald is accepted, because they are rarely pure. Grading terms specific to coloured stones vary from one laboratory to another.
Observing inclusions
A 10x magnifying loupe is enough. Light the stone from the side against a dark background, turn it slowly, and vary the angle. A few observations are within reach: the needles of a rutilated quartz, the moving bubble of an enhydro (tilt the stone gently), the flakes of aventurine, the crystals bristling from a tourmalinated quartz. Do not heat, rub or ultrasonically clean a stone with inclusions or fractures (emerald, fluid-bearing quartz): it could crack.
Frequently asked questions
Is an inclusion a flaw?
Not necessarily. It can reduce the value of a cut gem, but it often adds to the appeal of a collector’s crystal and proves that it is natural.
What is an enhydro?
A crystal (often quartz or chalcedony) that contains a cavity filled with liquid and a moving gas bubble.
How can glass bubbles be told apart?
They are often round and clean-edged, isolated or in lines. In a natural stone, cavities tend to have irregular shapes, with growth planes.
Can an inclusion be dated?
In some cases, yes, using laboratory methods, for example on enclosed zircons. This belongs to geochemistry, not to observation with a loupe.
Are insects in amber always genuine?
No. Genuine amber with fossil insects exists, but so do fakes. If you have doubts about an expensive piece, ask an expert for an opinion.
Also read
The meanings mentioned belong to tradition and symbolism. They are neither promises of results nor medical advice. Back to Mineralogy for beginners.