The perception of rarity in gemstones extends beyond the sheer amount of material available underground. Comparing rubies and diamonds requires distinguishing between the bulk supply of raw material and the availability of stones that meet the highest standards of gem quality. While diamonds are widely recognized and commercially abundant, true scarcity lies in the specific geological conditions and rigorous grading standards that elevate a common mineral into a highly valued precious stone.
Geological Formation and Bulk Abundance
The abundance of diamonds is tied to their formation deep within the Earth’s mantle, typically at depths of 90 to 155 miles. These gems are made of pure carbon crystallized under immense pressure and heat, brought close to the surface by rare, fast-erupting volcanic conduits known as kimberlite pipes. While diamonds form over billions of years, their transport mechanism means the raw material is geographically widespread across the stable cores of continents called cratons.
Rubies are a variety of the mineral corundum (aluminum oxide), and their formation process is inherently more localized. To achieve the signature red color, the corundum must incorporate trace amounts of chromium, an element generally rare in the Earth’s crust where rubies form through metamorphic processes. The simultaneous presence of aluminum, oxygen, and chromium under the specific high-temperature and pressure conditions needed for corundum crystallization is a much less common geological event globally than the deep-mantle conditions that produce diamonds. This makes the geological presence of ruby-forming material significantly less common than diamond-forming carbon.
Scarcity Defined by Gem Quality
Although diamonds are geologically common, the scarcity of gem-quality stones drives their value in the jewelry market. The industry prioritizes colorless diamonds, with D-Flawless stones being the ultimate ideal—a large, perfectly colorless, and internally clean crystal. Finding a diamond that is both large and free of inclusions visible under 10x magnification is an extremely high bar, which severely limits the supply of investment-grade diamonds.
The standard for rubies is dramatically different, resulting in a steeper drop-off in supply for top-tier stones. Rubies are graded primarily by color, with the most prized shade being the vivid, pure red known as “pigeon’s blood.” Most rubies naturally contain inclusions; unlike diamonds, some inclusions, referred to as “silk,” can enhance the stone’s color by diffusing light. However, the existence of a large ruby with saturated pigeon’s blood color and a high degree of transparency is exceptionally rare. This combination of intense color and high clarity in a large size means that top-quality rubies are exponentially scarcer than comparable high-quality diamonds.
Market Dynamics and Commercial Availability
Despite the geological and quality-based rarity of rubies, diamonds appear far more abundant to the average consumer due to distinct market dynamics. Historically, the diamond trade has been characterized by a centralized supply chain structure that effectively controls the flow of stones from mine to market. This tight inventory management has been successful in maintaining the perceived scarcity and price of diamonds, regardless of the volume of rough material being extracted.
The ruby market, in contrast, is much more fragmented, with many smaller mines and fewer mechanisms for global supply control. This structure leads to less consistent commercial availability and a less uniform marketing presence. Furthermore, aggressive, long-running marketing campaigns have saturated the consumer consciousness, cementing the diamond’s position as the default stone for significant jewelry purchases. This sustained effort creates a public perception of abundance that does not necessarily reflect the true rarity of the highest-grade stones.
The Final Rarity Comparison
The comparison of rarity ultimately depends on the definition of the stone being considered. In terms of bulk, raw material extracted from the Earth, the conditions for diamond formation are widespread enough that the mineral itself is not rare. However, once the strict standards of gem-quality are applied, the picture shifts dramatically.
High-quality, gem-grade rubies—especially those exhibiting the sought-after pigeon’s blood color in larger carat weights without significant inclusions—are significantly rarer than equivalent high-quality, colorless diamonds. This extreme scarcity is reflected in auction prices, where fine rubies often exceed the per-carat price of comparable white diamonds. While diamonds dominate commercial jewelry counters, the most perfect natural rubies represent a much smaller percentage of the total gem supply.