There are numerous kinds of inclusions that can be found in colored gems. Some inclusions are always found in certain gems and other inclusions are never found in others. This can help with identifying a gem. The next described flaws are some of the more common ones to look for:
Bubbles: These will look like tiny bubbles in many different sizes and shapes. Round bubbles can be found in natural amber however they usually indicate the item is synthetic or glass. In synthetic ruby or sapphire they can be seen as pear-shaped, round, profilated,or even tad-pole shaped. In pear-shaped and tadpole-shaped inclusions, the tail will always point in the same direction. You are likely seeing air bubbles in glass when numerous when there are numerous bubbles. An examination with a higher magnification is required when you see just a few bubbles since it must be determined if you are really seeing a true bubble or a small crystal.
Cleavage Fault: Instead of this being a true inclusion, it is a type of a break in the stone. It is often found in topaz, feldspar, diamond, kunzite and hiddenite. It can weaken the stone if exposed to high temperature change. In ultrasonic cleaning, the inclusion could become larger.
Curved Striae: These inclusions appear in old type synthetic sapphires and rubies. These inclusions will look like concentric curved lines. They can be very pronounced with the lines slightly curved and almost straight. They can be difficult to notice in pale synthetic pink sapphire. You can usually see them with a microscope.
Dark Ball Like Inclusions: These will usually appear as dark opaque balls surrounded by brown, wispy irregular shapes and found exclusively in Thai rubies.This inclusion will identify a genuine Thai ruby without any doubt.
Feather: This inclusion can be found either inside a stone or breaking the surface. One near the surface can weaken a stone and make it more apt for damage. Oiling of emerald may make the cracks harder to notice and is the reason one must be careful when inspecting. You can usually tell if a stone is genuine by cracks that have a rusty appearance to them. It is a good bet a stone is Lechleitner synthetic when there are numerous cracks in a web or fishnet pattern on the surface of a green stone that you think may be an emerald.
Fingerprint: These resemble fingerprints when small crystal inclusions are arranged in curved rows. They are often noticed in amethyst, citrine and other stones in the quartz family. Be careful you do not confuse them with the liquid filled healing feathers often seen in sapphires.
Flash Effect: This is an inclusion found in emeralds and looks like a flash of yellow or orange which turns to blue when the stone is tilted and you move the stone back and forth. This means there is an epoxy-resin filler. This type of inclusion can also be found in other gems, however the colors will be varied.
Halo Inclusions: These inclusions look like flat disc's. These can be found in many pastel colored Sri Lanka sapphires. These inclusions are the result of small fractures from the growth of zircon crystals inside the stone. Halos can also be seen in garnet.
Internal Growth Patterns: These inclusions are often the key when identifying synthetics. They appear as distinctive internal growth patterns.
Liquid Filled or Healing Feathers: These are often seen in sapphires and rubies as well as other gems in the corundum family. The appearance of liquid filled or healing feather inclusions resemble a maze of curved tiny tubes next to each other and separated by a space. They can look just like a fingerprint as well.
Needle or Feather Inclusions: These are sometimes referred to silk and look like very fine needles or fibers. These are found in almandine garnet,sapphire.ruby, and aquamarine.
Rain Inclusions: These inclusions are often found in flux grown synthetic rubies and appear like dashed lines which look like rain.
Swirl Marks: These inclusions look like curved swirl marks and are often seen in glass.
Three-Phase Inclusions: These inclusions appear like pea pad shapes that are pointed at both ends and contain bubbles. They are often found in Colombian emeralds. They can also be seen in Afghanistan emerald.
Tube Inclusions: These inclusions are often seen in Sandewana and Zambian emeralds and appear like long thin tubes.
Twinning Planes: These appear like parallel cracks and resemble panes of glass. They are often noticed in rubies and sapphires. These type of inclusions can often tell whether the ruby or sapphire is genuine.