The sapphire is one of the four traditional precious gemstones, distinguished by its deep blue colour. Lighter varieties of sapphire are mined in Ceylon. Like the ruby it is a variety of the mineral corundum.
Sapphires take their name from a Greek word meaning "blue stone". Also known as the "Stone of Heaven", during the Middle Ages the sapphire changed its identity—originally the name referred to lapis lazuli. The following is a list of blue gemstones known in medieval times:
- sapphire (also known as ultramarine; originally referred to lapis lazuli; changed its identity following the Crusades)
- cyan (azurite or poss. sodalite; also referred to a ceramic imitation of turquoise)
- callais (also known as turquoise; however, Pliny classed it as an emerald due to its greenish tint)
- hyacinth (the identity of this stone is problematic; most experts believe it refers to modern sapphire (corundum)—nevertheless, Pliny's description of a stone "weaker and more diluted in color than amethyst, whose beauty fades before it reaches the eye" seems to be a perfect description of iolite, a variety of the mineral codierite, also known by the trade name "water sapphire")
- Sydney H. Ball, A Roman Book on Precious Stones (includes Eng. trans. of C. Plinii Secundi liber xxxvii de Naturalis Historia), Los Angeles, 1950
- Cariadoc's "On gemstones"
- Eduard Gubelin & Franz-Xaver Erni, GEMSTONES: Symbols of Beauty & Power, Tuscon AZ, 2000
- Walter Schumann, Gemstones of the World, New York, (rev) 1997