Ruby formation in nature faces several challenges.

One of the primary conditions is that corundum, the mineral species of ruby, forms best in a low-silica environment.

Silica, which is the second most abundant element in the Earth's crust, can hinder this process. Additionally, rubies require a low-iron environment. While iron is the fourth most abundant element on Earth, its presence can alter the ruby's characteristics. Trace amounts of iron are acceptable and can contribute to the coloration of sapphires, including yellow and blue variants when combined with titanium. However, excessive iron results in orange sapphires rather than rubies.

The impact of iron is especially evident in the fluorescence of chromium, the trace element responsible for the ruby's signature red hue. Rubies with higher iron content, like those formed in basalt deposits, display a noticeable difference from those formed in marble deposits, such as those in Myanmar. The ruby from Myanmar, with a lower iron content, has a more intense fluorescence compared to the ruby from Mozambique's basalt deposits, which contains more iron.

Complications of Chromium in Rubies

Although chromium is only a trace element in rubies, it causes several complications in their formation. Unlike iron and titanium, which mix well with corundum and contribute to the vivid colors of blue sapphires, chromium's interaction with corundum is less harmonious. This difficulty in mixing with corundum limits the size and quality of rubies.

Sapphires, with their ability to reach enormous sizes—such as the 500-carat Star of India or the 470-carat Sapphire of Queen Marie showcase the vast potential for sapphire growth. In contrast, rubies rarely reach such large sizes due to chromium's complicated chemistry. The Sapphire of Queen Marie, a massive gemstone, is featured in a pendant worn by the Queen of Romania in various portraits. Interestingly, the sapphire hanging as the pendant is double the size of the largest sapphire in her crown.

While there are larger rubies, such as the Liberty Bell Ruby (weighing 8,500 carats), its opacity and carving-grade quality make it far less impressive than a fine-quality sapphire. The Liberty Bell Ruby also contains purple hues, which is common in rubies and often indicates the presence of trace iron and titanium—elements that interfere with the pure red of chromium. This illustrates why a low-iron environment is crucial for rubies to maintain their distinct color.

The largest fine-quality ruby ever recorded is the Hope Ruby, weighing 32 carats and sold for a staggering $6.7 million at auction. However, even this gem is a fraction of the size of the enormous sapphires, highlighting the inherent size limitations of rubies. In fact, the Sunrise Ruby, valued at $30 million, holds the title for the most expensive ruby, further emphasizing the rarity and value of fine rubies.

Complications with Crystallization

Another challenge in ruby growth is their natural crystallization habit. Rubies tend to form as flat, hexagonal tablet-like crystals. While some carving-grade rubies, like the Liberty Bell Ruby, can grow into larger, more complex shapes, their crystal structure limits the size to which rubies can grow. For example, the R2005 ruby (weighing 7,453 carats) from Sri Lanka showcases a more typical sapphire-like habit—tall and hexagonal.

In summary, rubies grow in a rare and complex environment, with trace elements causing inclusions that further complicate their formation. Even slight alterations in these elements, such as iron or titanium, can shift the ruby's red color toward purple or orange. Additionally, the natural crystallization pattern of rubies prevents them from forming large enough crystals for cutting into bigger gems. These combined factors make it incredibly rare to find rubies that are clear enough to be faceted into gemstones over one carat in size.