Rubies and sapphires are both varieties of corundum. Corundum is characterized by its high hardness and toughness. The Mohs scale, a standardized hardness scale for minerals, ranges from 1 to 10, with diamond, the naturally occurring mineral with the highest hardness, being assigned a rating of 10. Corundum is assigned a Mohs scale hardness of 9.
Mohs Scale of Hardness Explained
The Mohs scale of hardness is a measure of a gemstone’s resistance to scratching, ranging from 1 to 10, with talc at 1 and diamond at 10.
Durability in gemstones is also influenced by toughness. While diamonds exhibit high scratch resistance, they are susceptible to chipping when subjected to impact.
In contrast, corundum demonstrates superior resistance to impact compared to diamonds.
Trace Elements Found in Corundum
In its purest state, corundum presents as a colorless gemstone. Nevertheless, the presence of trace minerals is responsible for the diverse and vibrant colors observed in rubies and sapphires. Specifically, elements including magnesium, copper, chromium, titanium, and iron can affect the corundum’s coloration, leading to a spectrum of hues, ranging from blue and purple to green, orange, yellow, pink, and the distinct red characteristic of rubies.
Chromium: The Key to Rubies and Sapphires
Rubies and pink sapphires both obtain their coloration from chromium within the crystal structure. The primary differentiation resides in the chromium concentration, which replaces aluminum atoms within the corundum. An elevated chromium content within the crystal results in a deeper, more saturated red coloration of the corundum.
The Differences Between Rubies and Sapphires
This is a critical inquiry, as it underscores the inherent ambiguity within gemstone classification methodologies. Current scientific consensus indicates that the differentiation between pink sapphire and ruby is predominantly determined by chromium concentration. Nevertheless, this demarcation is not unequivocally defined. Gemstones exhibiting chromium levels within the range of 0.5% to 0.9% present a significant analytical challenge. Consequently, the question arises: At what specific point does a gemstone transition from being categorized as a pink sapphire to being designated as a ruby? The absence of a clearly established threshold results in diverse interpretations and classifications among gemological professionals and certifying organizations.
Other Factors Affecting Color
The coloration of a gemstone is also influenced by the cutting process. The orientation of the crystal during cutting can result in different color shades, such as various purples or oranges. Furthermore, the size of the gemstone has a substantial impact on its color, with larger stones typically appearing darker than smaller ones.
Why Does it Matter What it is Called?
The limited availability of rubies, coupled with increased market demand, leads to significantly higher pricing when compared to pink sapphires.
Even Professional Gemologists Disagree
The categorization of gemstones, specifically the differentiation between rubies and pink sapphires, continues to be a subject of considerable debate among prominent gemological institutions. Divergent methodologies and interpretations among these organizations result in inconsistencies in the classification of these aesthetically pleasing, yet complex, stones.
The Gemological Institute of America (GIA)
The Gemological Institute of America (GIA) categorizes rubies as corundum gemstones displaying a dominant red coloration. Although masterstones are utilized in the grading of rubies and sapphires, they acknowledge that the identification of the predominant hue may be subjective.
The International Gem Society (IGS)
The International Gem Society (IGS) categorizes both pink rubies and pink sapphires, differentiating them based on color intensity, with pink sapphires appearing as lighter in hue than pink rubies. However, various gemological associations present diverse perspectives regarding the classification criteria. Certain organizations consider any shade or intensity of red to be indicative of a ruby.
Who Decides What It Is Called?
The classification of gemstones, particularly the distinctions between orange and purple sapphires and rubies, remains a contentious issue. Since all are corundum and contain chromium, the determination of whether a pink stone is a sapphire or a ruby is multifaceted. The designation often depends on the mining location, color saturation, and, if certified, the classification provided by the certifying agency. If a gem is sourced from a region renowned for ruby production and exhibits the appropriate color saturation, it is likely to be labeled a ruby.
Is It a Pink Sapphire or Pink Ruby?
Ultimately, the designation of a pink gemstone as either a sapphire or a ruby is subjective, as both are varieties of corundum, differing primarily in subtle color variations.