What are fingerprints in gems?

Fingerprints in gems refer to internal characteristics typically formed by partially healed fracture planes. These unique patterns can resemble the shape of a human fingerprint and provide significant information regarding the gem's formation and durability. The presence of these "fingerprints" indicates past events in the stone's geological history, such as pressure and temperature changes, that caused the fractures to form and later partially heal.

When these fractures occur, they can trap tiny amounts of foreign materials or create a unique pattern that further aids gemologists and appraisers in identifying the gemstone. The distinctiveness of these internal features contributes to the overall identification and valuation process of colored stones, making them critical elements during analysis.

As for the other options, while surface blemishes or natural decorations might refer to exterior qualities of the gem, and phosphorescent inclusions can describe another specific type of inclusion, they do not encompass the internal nature of "fingerprints" as described in gemological terms. Hence, understanding that fingerprints are a direct result of internal structural changes points directly to the concept of partially healed fracture planes within the gemstone.