Sapphire was gemstone-quality corundum, which was commonly blue, but also occurred in several other shades, depending on the amount of iron, titanium, vanadium, and other elements found in their make-up. The term sapphire was also typically associated with color of deep blue, such as that of sapphire wine. (DS9: "Second Sight")
By the mid-23rd century, synthesizing technology had become sophisticated enough that sapphires could be easily created in large quantities, whenever needed, greatly reducing their value. Standard technology aboard the USS Enterprise was capable of performing this process.
In 2267, Korob attempted to bribe Kirk, Spock, and McCoy with gemstones, including sapphires. However, because of an error in his telepathic scan, Korob mistakenly believed these stones were valuable. (TOS: "Catspaw")
In the holodeck adventure Julian Bashir, Secret Agent Bashir, posing as geologist Patrick Merriweather, had his knowledge of gemstones tested by Dr. Noah introducing him to a statue encrusted with rubies, tourmaline, sapphires and topaz. Merriweather identified the stones as "a most striking collection," and surmised, based on the ruby color, that the gemstones likely originated from the hydrothermal deposits of the Tibetian plateau region. (DS9: "Our Man Bashir")