Which came first: the inclusion or the gem?
Studying gemstones’ inclusions help to determine when were they formed before, during or after the development of a crystal.
Liquid inclusions in beryl (2023)Instituto Gemológico Español (IGE)
Gem’s inclusions are internal features in a gem material. We can find different kinds of inclusions, which are very important to study gem identification and to graduate their quality.
Inclusions in hyaline quartz from Berbes (Spain) (2017)Instituto Gemológico Español (IGE)
There are many ways to classify them, according to their state of matter (solid, liquid, gas), morphology or genesis, as we shall see.
Protogenetic inclusions
Protogenetic inclusions are pre-existing materials that were formed before the growth of its host, being trapped inside during the crystallization process.
Pyrite inclusions in a brazilian quartz (2017)Instituto Gemológico Español (IGE)
Protogenetic inclusions are solid, and they do not show a characteristic spatial distribution.
Syngenetic inclusions
Syngenetic inclusions may be minerals or fluids that were formed at the same time as its host. They are genetically or geochemically related to the host.
Color zoning in watermelon tourmaline (2023)Instituto Gemológico Español (IGE)
In addition to solids and fluids, growth lines are also considered syngenetic inclusions. They are stretch marks or banded areas produced by changes in the mother solution or in the crystallization conditions.
“Raindrops” in aquamarine (2023)Instituto Gemológico Español (IGE)
Some exsolutions, like the one pictured above, are also syngenetic. They once were minerals in solid solution phase that later have unmixed during cooling process or pressure changes, forming small crystals in the form of drops.
Needles in garnet (2023)Instituto Gemológico Español (IGE)
Exsolutions may also have needle shapes, as those shown in the image, or plates… Or even may produce special optical phenomena as silks or asterism, which is a reflection of the light in the surface of a polished cabochon that looks like a star of 4 or 6 rays.
Epigenetic inclusions
Finally, epigenetic inclusions are those formed after the host has, being produced by changes in temperature or pressure conditions, foreign materials o recrystallization.
Metamitic halo in topaz (2023)Instituto Gemológico Español (IGE)
Halos formed around a pre-existing inclusion are considered as epigenetic inclusions, as well as cleavage or stress marks produced by the tension to which they were subjected during treatments or hits, that can be filled with oxyds or other materials.
Foto credit: Ana de Bustos Ruiz, Manuel Fernández Lama, Egor Gavrilenko, José Alonso
Written by: Irene Gobet. Text revision: Marta del Teso, Almudena Gómez
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