Rubies are minerals, meeting the specific scientific criteria that define such substances. Their classification stems from their formation processes and inherent physical and chemical properties. Understanding what constitutes a mineral provides clarity on why rubies fit this category.
What Defines a Mineral
A mineral is a naturally occurring, inorganic solid with a definite chemical composition and an ordered atomic arrangement. These five universally accepted criteria are fundamental for classifying any substance as a mineral.
It must form through natural geological processes, meaning it was not created or significantly altered by human activity. Minerals are inorganic, signifying they do not originate from living organisms or organic compounds. They must exist in a solid state at normal temperatures and pressures, distinguishing them from liquids or gases, and possess a definite chemical composition.
The internal structure is an ordered atomic arrangement, also known as a crystalline structure. This means the atoms are arranged in a repeating, predictable pattern. This ordered structure gives minerals their characteristic crystal forms and physical properties.
The True Identity of a Ruby
Rubies are a variety of the mineral corundum, composed of aluminum oxide (Al₂O₃). This mineral typically forms in metamorphic rocks under high pressure and temperature.
The crystalline structure of ruby belongs to the trigonal system, characterized by a repeating, ordered arrangement of aluminum and oxygen atoms. This structure contributes to ruby’s hardness, ranking 9 on the Mohs scale.
The characteristic red color of a ruby arises from trace amounts of chromium (Cr³⁺) replacing some aluminum (Al³⁺) ions within this crystal lattice. Even small percentages of chromium are sufficient to impart the vibrant red hue. Chromium ions absorb specific wavelengths of light, allowing red light to be transmitted. This gives rubies their distinctive appearance.
Natural Versus Synthetic Rubies
The distinction between natural and synthetic rubies lies primarily in their origin, even though they can be chemically and structurally identical. Natural rubies form over millions of years through geological processes. These conditions result in unique internal characteristics, such as inclusions and growth patterns, that serve as fingerprints of their natural origin.
Synthetic rubies are created in laboratory settings by humans. Manufacturing processes, such as flame fusion, aim to mimic natural conditions to grow ruby crystals. While they replicate the chemical composition and crystalline structure of natural rubies, they do not meet the “naturally occurring” criterion for mineral classification.
Lab-grown rubies often exhibit different internal features, like curved growth lines or microscopic gas bubbles, which distinguish them from natural specimens. Synthetic rubies are not considered minerals because they lack a natural geological formation.