Gemstones come in an incredible array of colors, from fiery reds to oceanic blues. But not all blue gemstones are created equal. Some, like sapphires and aquamarines, are relatively common. Others are so rare that only a handful of specimens exist in the world. So what is the rarest blue gemstone? Let’s take a look at some of the contenders.
Blue Diamond
Diamonds come in various colors depending on the presence of trace elements and structural defects in the crystal structure. Blue diamonds are exceptionally rare, making up less than 0.1% of diamonds worldwide. The few blue diamonds that exist range from pale blue to deep blue. Famous examples include the Hope Diamond in the Smithsonian and the Wittelsbach-Graff Diamond at 31.06 carats.
Some key facts about blue diamonds:
| Proportion of blue diamonds | Less than 0.1% |
| Cause of color | Boron impurities |
| Hue | Pale to deep blue |
| Most expensive sale | $3.93 million per carat for the Wittelsbach-Graff Diamond |
While extraordinarily rare and valuable, blue diamonds are not the absolute rarest blue gemstone.
Blue Garnet
Garnets occur in many colors, including a rare blue variety. Blue garnets belong to the mineralogical species called color-change garnets. These display a different color depending on the light source, appearing blue under daylight but purple under incandescent light.
Only a handful of blue garnet specimens exist worldwide. The cause of the color change is the presence of vanadium and chromium ions. Some key facts:
| Species | Color-change garnet |
| Color | Blue in daylight, purple under incandescent light |
| Cause of color | Vanadium and chromium ions |
| Known specimens | Fewer than 10 in the world |
The extreme rarity of blue garnets makes them highly coveted by collectors. But there may be an even rarer blue stone out there.
Blue Benitoite
Benitoite is a rare mineral found in gem quality only in San Benito County, California. It fluoresces an intense blue color under ultraviolet light. Natural blue benitoite is dichroic, displaying violet-blue and clear blue shades depending on the viewing angle.
Benitoite is the official state gem of California. It has a high dispersion rating, meaning it exhibits exceptional “fire” like a diamond. But benitoite occurs in small sizes, with most faceted stones under one carat.
| Occurrence | San Benito County, California |
| Color | Violet-blue, pleochroic |
| Cause of color | Trace titanium, iron, and manganese |
| Size | Most specimens under 1 carat |
Due to its limited occurrence, small specimen sizes, and demand from collectors and museums, fine blue benitoite may very well be the rarest blue gemstone in the world.
Blue Painite
First discovered in the 1950s in Myanmar, painite is an exceptionally rare borate mineral. For decades, only a few specimens existed. But recent finds in Myanmar have unearthed over 200 crystals, most only suitable for scientific collections.
Natural blue painite possesses a striking electric blue color similar to fine blue Paraíba tourmalines. The cause of its color remains unknown. Intriguingly, painite is not blue when artificially synthesized.
| Discovery | 1950s Myanmar |
| Color | Electric blue |
| Cause of color | Unknown |
| Recent finds | Over 200 crystals in Myanmar |
Given the scarcity of blue painite and its stunning color, this gemstone is a top contender for the rarest blue. But it still may not be number one.
Blue Tanzanite
Tanzanite is the blue to violet variety of the mineral zoisite. It formed through the metamorphism of ruby deposits and derives its color from vanadium. Tanzanite is commercially mined in only one location: Tanzania.
Most tanzanite is heated to achieve the preferred blue color. Blue is the rarest hue for unheated, natural tanzanite. These coveted stones display a vivid blue without any trace of violet. Less than 1% of tanzanite has this magical blue color.
| Occurrence | Tanzania |
| Color | Vivid blue |
| Cause of color | Vanadium |
| Blue proportion | Less than 1% of tanzanite |
Based on geographic availability and the improbability of hitting the jackpot on color, blue tanzanite is arguably the rarest blue gem on Earth.
Blue Beryl
Beryl is best known as the mineral species that includes emerald and aquamarine. Blue beryl is an almost unbelievable rarity. Unlike emerald and aquamarine, it does not form in large crystal formations. Most blue beryl occurs as microscopic crystals in lithium-rich pegmatites.
The brilliant blue color results from trace amounts of cesium ions. Cuttable crystals over one carat are virtually unheard of. The few faceted examples in museums and private collections are considered priceless.
| Occurrence | Microscopic crystals in lithium pegmatites |
| Color | Cobalt blue |
| Cause of color | Cesium ions |
| Specimens | Less than 5 cut crystals in the world |
Based on size and availability, blue beryl is perhaps the rarest, most coveted blue gemstone on the planet.
Conclusion
Determining the definitive rarest blue gemstone is no easy task. All the contenders above occur in extremely limited quantities and have stories of their own.
Based on the microscopic size and near impossibility of finding cuttable rough, blue beryl has a strong claim to the title. Painite and benitoite are also incredible rarities, known from just a handful of localities.
Tanzanite, garnet, and diamond can also make a case in terms of exceptionally rare color hues. There may even be other little-known blue gems waiting to be discovered.
Part of what makes colored stones so appealing is their diversity, uniqueness, and unpredictability. The rarest blue gem may still be out there, waiting to be unearthed.
