Sapphire is definitively not a quartz, as these two materials belong to entirely separate mineral species based on their fundamental chemical makeup and internal structure. The two minerals are classified into different groups of the mineral kingdom, indicating a profound difference in their formation and properties. Understanding these distinctions requires looking closely at the defining characteristics of each mineral.
The Identity of Sapphire Corundum
Sapphire is a gem variety of the mineral corundum, which is composed of aluminum oxide. Corundum is an oxide mineral that forms when aluminum and oxygen atoms bond together in a rigid crystalline lattice. The chemical structure of corundum is highly stable, which contributes to its exceptional physical durability.
The colors of sapphire, which include the classic blue, along with yellow, pink, purple, and green, are determined by trace impurities within the aluminum oxide structure. For instance, the presence of small amounts of iron and titanium ions creates the characteristic blue color. If chromium is the dominant trace element, the corundum is classified as ruby, the red variety of the same mineral species.
Corundum crystallizes in the trigonal system, characterized by a three-fold rotational symmetry axis. This specific atomic arrangement is a direct consequence of the way the aluminum and oxygen ions pack together under high pressure and temperature.
The Identity of Quartz Silica
Quartz is a widespread mineral composed of silicon dioxide, also known as silica. It is the second most common mineral in the Earth’s crust, found in nearly every geological environment. Quartz belongs to the silicate mineral class, specifically a group known as tectosilicates, or framework silicates.
The structure of quartz consists of a continuous framework of silicon-oxygen tetrahedra, where each oxygen atom is shared between two silicon atoms. This interlocking structure is what makes quartz chemically resistant to weathering and physically hard.
Quartz crystals typically form a hexagonal structure, which is evident in its characteristic six-sided prism shape capped by six-sided pyramids. Quartz occurs in numerous varieties, such as amethyst, citrine, and rose quartz, with colors resulting from various impurities and radiation exposure. The chemical foundation of silicon and oxygen sets it apart from the aluminum-based composition of corundum.
Distinguishing the Two Hardness and Crystal Structure
The most significant physical distinction between the two minerals lies in their resistance to scratching, measured by the Mohs scale of hardness. Corundum, of which sapphire is a variety, registers a 9 on the scale, making it one of the hardest natural minerals, second only to diamond. Quartz, by contrast, has a hardness of 7, meaning a sapphire can easily scratch the surface of quartz.
This difference in hardness is a direct result of their internal atomic arrangements and chemical bonds. The denser packing of aluminum and oxygen atoms in the trigonal corundum structure creates stronger inter-atomic forces than those found in the hexagonal silicon-oxygen framework of quartz. This structural disparity is also reflected in their density.
Sapphire has a noticeably higher specific gravity, clustering around 4.00, meaning it is four times denser than an equal volume of water. Quartz has a much lower specific gravity, typically around 2.65. This difference means that a sapphire gemstone will weigh significantly more than a quartz gemstone of the exact same size and shape.