Which material do rubies from marble deposits typically have low levels of?

Rubies that originate from marble deposits are characterized by their low levels of iron content. This is significant because the presence of iron can affect the color and clarity of the ruby. In marble deposits, the formation of rubies often occurs in a high-grade metamorphic environment, where aluminum-rich minerals are prevalent in the metamorphic rock, allowing for the incorporation of aluminum into the ruby structure.

While aluminum is an essential component of corundum (the mineral family to which rubies belong), its levels are typically higher in marble deposit rubies due to the geological conditions under which they form. Similarly, silicon and calcium are less relevant in this context. Silicon is a major component of silicate minerals, but rubies are primarily aluminum oxides. Calcium is often more associated with the marble itself rather than with the rubies formed within it. Therefore, the distinguishing factor for rubies from marble deposits is their notably lower iron content compared to rubies sourced from other types of deposits.