Alphidium was a substance with an extremely high melting point. It was used by the Federation to make the casings of telemetry probes.
History and specifics[]
In 2269, pairs of telemetry probes were launched by the USS Enterprise to investigate a temperature anomaly in the Beta Castelli vicinity in sector 79F. Due to the presence of a protouniverse expanding from a baryon conversion rift, the alphidium casings melted, causing to the probes to stop functioning. (TOS novel: The Three-Minute Universe)