Needle- A long thin inclusion that can be solid crystal or hollow tube and it might be filled with liquid or gas.
Silk-Groups of fine needle inclusions. This type of inclusion can create very attractive stones. An example of this is a star stones and cats eye stones.
Fingerprint- This type of inclusions is exactly as its name sounds. It forms a pattern that often resembles a fingerprint. Also they are like a fingerprint in that no two are ever the same. They are actually a partially healed fracture plane. Droplets of fluid were trapped in the crystal before it stopped growing.
Feather-This is the general term for a break in a stone. The term includes any separation or break in a stone. It includes cleavages, parting and fractures if they have not been healed by the natural process. This can be a serious inclusion as it can affect the durability of the stone. If the feather is large this really becomes an issue.