Alpha 23-C was a planet located in sector 179, sub-sector 23-C of the the galaxy's Alpha or Beta Quadrant. It was home to several crystalline species, including a developing civilization of Alpha 23-C natives.
The planet was a treasure trove of rare minerals, but low in base metals. Its atmosphere was breathable, but apparently lacking in enough carbon and nitrogen to support organic lifeforms. Inhospitable topography included mesas, plateaus and caverns.
In 2266, during an exploration of the sector, Spock scanned the planet and theorized that some of its surface minerals could have applications for industry and scientific research. When Montgomery Scott tried to chip off a sample on the surface, however, it reacted by firing telepathic beams and displaying faceted imagery as a means of visual communications — it was sentient. The ship's landing party made first contact with the Alpha 23-C natives and helped defend them from a slourda dragon attack. (TOS comic: "The PsychoCrystals")