Precious Stones are minerals chosen for their beauty when cut and polished. Although they are not minerals, pearls and amber are often included as gemstones. In the 1800s, gemstones were categorized into precious and semi-precious stones. Today, those categorizations are often misleading and do not always reflect the value of the individual gemstone. The precious and semi-precious classification has many exceptions.
Traditionally, the Big Four Gemstones, diamonds, emeralds, rubies, and sapphires, were precious stones.
Diamonds are composed of carbon and are the hardest, most durable natural substances. They are one of the most popular gemstones because of their bright luster and reaction to light. However, the popularity of diamonds as precious stones has more to do with the aggressive marketing of the diamond industry that diamonds are rare and valuable. Truthfully, diamonds are one of the few gemstones with a consistent supply.
Emeralds are a variety of beryl minerals defined by their rich green color. Emeralds are considered fragile stones because of numerous surface-reaching fractures. Treating emeralds with waxes, oils, and polymers improves their appearance, but it does not improve durability.
Rubies are gemstones of the mineral corundum. Chromium gives it a beautiful red color. However, very few specimens have the color and clarity to produce a quality faceted ruby. Rubies are one of the most popular red gemstones.
Sapphires are also gemstones of the mineral corundum. They have the same chemical composition as rubies; only sapphires are blue because of trace amounts of iron and titanium. Sapphires are one of the most popular blue gemstones.
Traditionally, they were everything besides diamonds, emeralds, rubies, and sapphires. The name “semi-precious” is often misleading because there are rare semi-precious gemstones that are more valuable than precious stones. For example, Jadeite is the second most valuable gemstone in the world but is considered a semi-precious stone. Other valuable stones include Taaffeite, Grandidierite, Serendibite, and Black Opal. For this reason, most professional gemologists no longer use the terms precious and semi-precious for gemstones.