This section profiles the colored gemstones most often set in fine jewelry, from the classic "big four" to newer stars such as tanzanite and Paraiba tourmaline. Each profile covers the mineral behind the gem, what causes its color, where it is mined, how it is treated, what affects its value and how to care for it.
What "precious" used to mean
For a long time, Western jewelers sorted gems into two tiers. The precious stones were diamond, ruby, sapphire and emerald, sometimes with pearl added as a fifth. Everything else was called semi-precious. The split reflected what European buyers of the 18th and 19th centuries valued most: hardness, intense color, a long history in royal regalia, and limited supply from distant sources such as India, Burma, Ceylon and Colombia.
Those four do share real advantages. Diamond, ruby and sapphire are the hardest gems in common use, so they wear well in rings. Ruby, sapphire and emerald come in saturated colors that few other gems match. And fine examples of all four have always been scarce.
Why the term is loose today
The precious label has never had a scientific or legal definition, and it does a poor job of describing value. A fine alexandrite, Paraiba tourmaline or red spinel can cost more per carat than an ordinary ruby or a cloudy emerald. Low-grade sapphire sells cheaply by the parcel. Gems such as tanzanite, discovered in 1967, did not exist on the market when the old list took shape.
Professional gemologists now judge each stone on its own color, clarity, cut, size, treatment and origin. That is why this section includes stones that older books would have called semi-precious. The semi-precious gemstones section covers the remaining gem families, and both sections use the same profile format.
How the profiles are organized
Each gem profile opens with a quick facts box: mineral species, chemistry, Mohs hardness, crystal system, refractive index, specific gravity and main sources. The body then works through the same questions in roughly the same order:
- What the gem is and what gives it color.
- Varieties and trade names, such as padparadscha sapphire or rubellite tourmaline.
- Where it comes from, with links to regional pages such as Muzo and Colombian emeralds or Mogok ruby.
- Treatments and synthetics.
- How quality and value are judged.
- Care, durability and folklore.
Treatments get their own pages for the gems where they matter most, such as ruby treatments and sapphire treatments. For the methods that apply across many gems, see gemstone treatments explained.
Garnets and other gem families
Some names cover a whole family of minerals. Garnet is a group of related silicates, and its profile links to separate pages on almandine, andradite (including demantoid), grossular (including tsavorite), spessartite and uvarovite. Tourmaline is also a group, with Paraiba tourmaline profiled on its own because of its copper-based neon color. Quartz gems such as amethyst, citrine and ametrine share one mineral but have separate pages.
Birthstones
Most of the gems in this section appear on the modern birthstone list, from January's garnet to December's tanzanite and zircon. The birthstones by month chart lists them all with links, and each profile notes its month. If you are buying, start with how to buy a gemstone and the gemstone durability guide, which helps match a gem to the type of jewelry it will go into.
Frequently asked questions
What are the four precious gemstones?
Traditionally diamond, ruby, sapphire and emerald. The grouping is historical and has no scientific or legal standing.
Are precious gems always worth more than semi-precious ones?
No. Value depends on the quality of the individual stone, and a fine example of a so-called semi-precious gem can outprice a low-grade ruby or emerald.