Stones Identification By Internal Inclusion Types Observations

Stones Identification By Internal Inclusion Types Observations

Today, we will discuss how gemstones and minerals are identified through internal observations of inclusions?. What are their characteristics and how many types of inclusions are found? Stones are identified by two different methods through observations. 

  1. External Mineral Observation
  2. Internal Mineral Observation

External observation focuses on the cut, polish,

 7 Crystal Systems and their Shapes. Learn this also

scratch, abrasion, and pits. This helps us in judging stone quality. In this article, we will focus on internal observation which is linked with internal inclusion types in the stones. Scientists have recorded various type of inclusions in different stones by which a stone is identified regarding its being fake, original or stone type.

What gemstones and minerals Inclusion is called?

Let us first see what is inclusion called in any stone?

Inclusion is an outside, a part of a host rock, or from the mineral itself material or substance which is trapped in the mineral when they take the form from high pressure and temperature. It can be another mineral, element in form of solid, liquid, gas, fractures etc. Discovery of new inclusion types is going on with the passage of time. The list of inclusion type is not fixed to only a few. It is ongoing research work. Scientists and researchers keep on building new find inclusions in the list of gemstones.

Here are a few types of inclusions, researchers have observed:-

  1. Bubbles: Usually comes in gas bubbles.
  2. Needles: Looks like needles or fibers. examples: tourmaline, quartz, ruby, sapphire, tourmaline.
  3. Silk: Needles appear like silk feathers or fabric. It is usually found in ruby and sapphire.
  4. Feather
  5. Crystal: another solid crystal inside the mineral
  6. Cleavage fault: upper or internal cracks usually found in Kunzite, diamonds, topaz.
  7. Rain: Dash ---- like lines
  8. Color zoning: uneven distribution of color of the gemstone. Frequently observed in corundum, amethyst.
  9. Dendritic: internal natural scenery like  moss-agate
  10. Halo or Disk:  small fractures resulting from the growth of zircon crystals inside the host stone. Other examples are garnet
  11. Twinning: Looks like parallel cracks usually found in corundum. An important mark for their being true or authentic.
  12. Veils: small bubble

The inclusion in the stone will be called as the imperfection of the stone. However, in the identification of gems and minerals, inclusions play an important role. If your gemstone is having inclusion, no worry. It is good. It marks the stone is natural. Though sometimes, inclusion weakens the stone.  Sometimes, thy increase the beauty of mineral like you see in petroleum quartz or pyrite inside lapis.

Two-Phase Inclusion in Petroleum Quartz under UV Light

Types of Inclusions

Minerals normally have the following type of inclusions. It can be solid, liquid or gas.


Solid inclusion will have inclusions in form of needles, fiber, crystals III shapes and so on.  An example is rutile or tourmaline needles in rutile quartz, calcite crystals in emerald, olivine in diamond, apatite in sapphire. This is a result from crystallization process of mineral at the initial or last phase.

Tip to Identify from Solid: Check needles, fiber, III crystal shapes.


The liquid can be in form of shiny fingerprints. The heat treatment can lower down the fingerprint inclusion. This is not common type inclusion. The liquid usually turns into gas or vapor at high temperature forming the gas inclusion in the final stage during the mineral cools down to the room temperature. The liquid must form in low temperature and pressure in low depth deposits.


Gas inclusion can be in form of bubbles. When mineral cools down to room temperature, homogeneous fluid separate in 2 phases i.e. gas and liquid. Gas bubbles take formation at high temperature and pressure. Glass bubbles are found in glasses i.e. moldavite, obsidian, Libyan glass, and synthetic stones like ruby, sapphire normally. However, they are found in natural gemstones also. Gas bubbles take form by solidification of melted substances. Bubbles shapes are normally elongated and spherical rounded.


Tip: How you will identify from bubble if the stone is natural or unnatural?

In synthetic stone or glass, the gas bubbles will be in good/smooth shapes. They will be occasionally in well-rounded shapes. In natural gemstones, bubbles will have free shapes.

Classification of Gems an Mineral Inclusions

Apart from the physical state of inclusions, the stone will have combinations of different phases. It means the stone can have more than 1 type of above inclusion. It can have solid, gas and liquid at a time. It is possible that the other material inside the mineral will have gas or liquid also. Here is when the term " phase " is used. 2 different minerals inside the mineral-like 2 different solid or liquid or gas can be two-phase inclusion.

Inclusions Phases can be further divided in the following counting:-

  1. Single phase Inclusion
  2. Two-phase Inclusion
  3.  Three phase Inclusion
  4. Multiphase Inclusion

Single Phase Inclusion: Single phase inclusions usually have solid material most of the time. Common solid particles are trapped inside the mineral. It can be a host rock or others outside minerals. Gases single phase inclusion is usually found in glasses or synthetic stones. It happens when they form from melting. Gasses single-phase inclusion is found also in natural gemstones also like Quartz is common to have gas bubbles. Single phase is not common. Because a mineral takes formation at high pressure and temperature under the earth. How gems and minerals take form under the earth, it can help you to understand. When the mineral cools down to room temperature after formation, homogeneous fluid separate in 2 phases i.e. liquid and gaseous. This condition form two-phase inclusion like liquid and vapor.

Two-Phase Inclusions: As it shows by the name, 2 phase inclusions mean a mineral is having 2 type of inclusions. It can be solid, liquid. It can be liquid and gas. The process is the same. When a mineral cools down to the room temperature after taking formation from high pressure and temperature, homogeneous fluid separate in 2 phases at the very initial step. This condition forms 2 phase inclusions such as liquid and vapor. Examples are liquid hydrocarbons (Petroleum) and Co2. Usually found in petroleum quartz.

Three phase Emerald Inclusions

 Elongated needle-like multiphase inclusions, hosting several crystals and gas bubbles, in emeralds from the Kamar Safeed area near Khenj in the Panjshir Valley. Photomicrographs by S. Saesea

Three-Phase Inclusions: By the term, three phase means that the stone is having three types of inclusions. When a fluid trapped in cavity separate itself in three different phases after cooling down to the room temperature. They are normally coming in liquid, solid, vapor or liquid +  liquid + vapor. An example is Columbian emeralds. Another example is liquid petroleum inclusions which are contained in a fluid. This is usually visible through UV Light.


 Liquid, Gas, Solid three-phase inclusions in Petroleum Quartz

Multi-Phase Inclusions: In multi-phase inclusions, you can see a combination of different types of inclusions in more than three phase. In fact, inclusions having more than three phases will be called multi-phase inclusion. Such phenomena in any gemstone are very rare. In this type, you will see a combination of solid, liquid, water, bubbles or any uniqueness. In this case, two or more different compounds are precipitated from the fluid inside the inclusion cavity.

Inclusions in Natural Gemstones and Minerals

Natural gemstones are more valuable than synthetic. They are valuable because they are natural. However, identification of natural gemstones is a key question while selection and need powerful skills. Inclusions are the key points which can help you initially in determining whether you are going to have a genuine gemstone or not. Natural gemstones will have certain inclusions which are usually not found in synthetic. Examples are below mentioned.

  • Needles
  • Crystals
  • Fluids
  • Clous
  • Imperfect bubbles
  • Rutile hairs
  • tourmaline hairs
  • silk fingerprints
  • twinning

There is a long list of inclusions found in natural gemstones.

Inclusions in Synthetic Gems

Synthetic gemstones are created in labs. Synthetic gemstones normally have bubbles and fingerprints. The shape of bubbles is usually well rounded. Heat treatment lowers down the appearance of fingerprints in natural corundum like ruby and sapphires. Synthetic glass like obsidian, moldavite will have gas bubbles in well-rounded shapes.  Flux fusion is usually grown in corundum. Cheap rubies and sapphires will have no crystal or silk inclusions.

trapped flux residue apparent. Photomicrograph by Nathan Renfro[/caption]

You need to check doublet stones which are glued. Glue will be visible between two layers of stones.

Tips for Viewing Inclusions in Gemstones and Minerals

  • Use the best lighting surroundings and environment.
  • You can use polariscope. How gemstones are tested through polariscope, you can learn this here also.
  • UV Light, Fluorescent light to see the light, dark field. You can use any type of lights. Which will give you various information about the inclusions?
  • Use Loop or mini microscope if possible.
  • Look through the wide and broadest window into the gem. It can be table facet / Pavilion.
  • Keep the gems, rocks and mineral into the variety of angles.


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1 comment

Thank you, that was very interesting.

Keith Nickol

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