The gemstone business in the past was dominated by the “big three,” ruby, emerald, and sapphire. These gemstones have always been the most popular and the market for these stones is different than the market for other gemstones in many ways.
When other gemstone varieties began to be popular in jewelry, the jewelry industry got tired of calling them “colored gemstones other than ruby, emerald and sapphire.” People needed a term to distinguish these other gems from the big three, since all of them can be called colored gemstones. Unfortunately, the term they made up was “semi-precious” since the big three were often called precious stones, probably from the French “pierres precieuse.” Unfortunately the French terminology was not followed for the other stones or they would be known as “fine gemstones,” which is much better than that semi word.