Turquoise
Turquoise is a distinct mineral species — a hydrated copper-aluminum phosphate — valued for its color long before modern mineralogy could explain it: the blue comes primarily from copper, while iron impurities can shift material toward green. Unlike many gems that occur as clear crystals, turquoise forms as a compact, often opaque mass, typically as veins or nodules within host rock, which is why much natural turquoise shows a web of darker “matrix” — remnants of the surrounding rock — running through it.
Iran (historically Persia) has long set the benchmark for the finest turquoise: an intense, saturated, relatively matrix-free sky blue that collectors and the trade still reference as “Persian blue” regardless of actual origin. American Southwest material, notably from the United States, more often shows pronounced matrix veining, a look prized in its own right rather than treated as a flaw, especially in Southwestern and Native American jewelry traditions. China and Egypt (with some of the oldest documented turquoise mining in the world, dating back millennia in the Sinai) are also significant sources.
Turquoise sits at Mohs 5 to 6 — noticeably softer than quartz — and, just as importantly, it’s porous. That porosity means it can absorb skin oils, lotions, perfume, and household chemicals over time, which can permanently dull or discolor the stone; many commercial pieces are treated with a stabilizing resin specifically to reduce this vulnerability and improve consistency, a widely-used and generally disclosed practice worth asking about when buying. Turquoise jewelry is best kept away from cosmetics and cleaned gently with a dry or barely damp cloth, never soaked or ultrasonically cleaned.
Turquoise’s birthstone month has genuinely shifted over time, which makes it a good example for this site’s broader point. On the historical 15th–20th-century list, it’s a secondary July stone (with onyx), a month the current lists instead give to ruby alone. By the time of the US 1912 list, turquoise had moved to December (paired with lapis lazuli), and it has stayed there since — the UK 2013 list pairs it with tanzanite, and the current US list pairs it with both zircon and tanzanite, making December the most crowded month on that list. Turquoise doesn’t appear on either zodiac birthstone system tracked here.
Gemmological properties
| Mohs hardness | 5–6 |
|---|---|
| Crystal system | Triclinic |
| Chemical formula | CuAl6(PO4)4(OH)8·4H2O |
| Refractive index | 1.61–1.65 |
| Color family | Blue, Green |
| Variety of | — |
| Also known as | — |
| Origins | Iran, United States, China, Egypt |
| Organic material | No |
Persian (Iranian) turquoise is the historic benchmark for the finest, most saturated sky-blue color; American Southwest turquoise more often shows the matrix veining collectors also prize.
Where Turquoise appears as a birthstone
By month
Frequently asked questions
- Why does turquoise need more careful handling than harder gems?
- It's both relatively soft (Mohs 5 to 6) and porous, which means it can absorb oils, perfumes, and household chemicals that permanently discolor it over time — turning greenish or dull. Many commercial turquoise pieces are also stabilized with a resin to improve durability and color consistency, which is worth asking about since it affects long-term care and value.
- What causes the color difference between Persian and American Southwest turquoise?
- Both are the same mineral, but differ in trace chemistry and matrix. Persian (Iranian) material is historically prized for a saturated, matrix-free sky blue, while American Southwest turquoise more often shows visible veining ('matrix') from the host rock it formed in — a look collectors value differently rather than a quality defect.
- Has turquoise always been a July stone, a December stone, or both?
- Both, at different points — it's a secondary July stone on the historical list and a December stone on the US 1912, UK 2013, and current US lists, making it one of the few stones whose birthstone month genuinely moved across the 20th-century standardization.