Precious and Semiprecious Gems

For centuries, people have used the terms “precious” and “semiprecious” to describe gemstones. You’ll still occasionally hear these terms today. However, this gem classification has so many exceptions it has no real value. For example, diamonds have traditionally been considered precious gems, yet some sell for $100 a carat. You can see them (with sufficient magnification) as accent stones on inexpensive jewelry. On the other hand, garnet gems have traditionally been considered semiprecious gems, yet some sell in excess of $1,000 a carat, ten times the price of a low-quality diamond.

Referring to a set of gem types as “precious” and all other gems as “semiprecious” can be misleading, since it implies precious stones have inherently greater value. Professional gemologists no longer use these terms. If you encounter these descriptions, buyer beware.

Diamonds and Colored Stones

You’ll also commonly find gems divided into two other categories: diamonds and colored stones. (Some dealers use the shorthand “color” for colored stones). All gems other than diamonds fall into the “colored stones” category. Gem cutters and dealers use this gem classification system for two main reasons.

First, cutting diamonds requires special tools because these gems are harder than all…