What is the difference between a precious stone and a semi-precious stone?

Precious stones and semi-precious stones are terms that were created in the mid-1800’s to describe gemstones, which were categorized solely based on their rarity. Stones found in abundance were labeled semi-precious, and a stone that was rare would be categorized as precious and more valuable. Diamonds, rubies, sapphires, emeralds were classified as precious stones. All other stones are classified as semi-precious stones. The distinction between precious and semi-precious stones are their rarity and their quality. Despite this distinction and classification of precious stones vs. semi-precious stones, it is not necessarily true that a precious stones is always more valuable or rare than a semi-precious stone. For ex. a green garnet known as Tsavorite is classified as a semi-precious stone, however, it is more valuable than an emerald, which is classified as a precious stone. Now, value is measured by several different factors, and precious stones often do not hold more value than semi-precious stones. However, the label is still valuable and is used worldwide to promote and sell jewelry.