A crystal is a solid material whose constituent atoms or molecules are arranged in a highly ordered, repeating pattern, forming a crystal lattice. This internal regularity distinguishes true crystals from amorphous solids like glass, which have a random atomic structure. A popular belief among collectors is that a genuine crystal will always feel significantly cold to the touch, suggesting this sensation indicates authenticity. This article explores the physical science behind the cool sensation minerals often possess and clarifies why relying on temperature alone is an unreliable method for identification. It offers practical methods to determine if a crystal is real.
The Science Behind the Cold Sensation
The sensation of coldness when touching a crystal is not due to its actual temperature, which is typically the same as the surrounding air. This feeling is a physical phenomenon rooted in heat transfer, where thermal energy moves rapidly from a warmer object (the skin) to a cooler one (the crystal). When a person touches a crystal, the heat from their skin is quickly transferred into the stone.
Crystalline materials, especially dense minerals like quartz, possess high thermal conductivity. This property allows heat to move quickly through the material, drawing it away from the point of contact faster than materials with lower conductivity, such as wood or plastic. The speed of this heat transfer is governed by the material’s thermal effusivity.
The rapid removal of heat triggers nerve receptors that register a drop in temperature, creating the immediate sensation of coldness. Since crystals are generally denser and better heat conductors, they feel distinctly cooler than the surrounding air, though this feeling quickly fades as the crystal’s surface warms.
Why Coldness Does Not Guarantee Authenticity
Although rapid heat transfer is a property of many genuine crystals, the cold sensation is not a definitive test for authenticity. This effect can be easily replicated by materials that are not true minerals. Many common fakes, especially those made from high-density glass or certain synthetic materials, are dense enough to exhibit sufficient thermal conductivity to mimic the cooling effect and fool a casual touch test.
Furthermore, a genuine crystal may not always feel cold, leading to a false negative. Some natural minerals, such as raw selenite or certain soft stones, have a less dense or more porous structure. This results in lower thermal conductivity, meaning these genuine specimens will feel closer to room temperature.
The cold test is also unhelpful when dealing with lab-grown or synthetic crystals, such as hydrothermal quartz. These stones are chemically and structurally identical to their natural counterparts. Since synthetic stones possess the same high thermal conductivity as natural ones, they will also feel cold to the touch. The physical sensation of temperature confirms only a material’s thermal properties, not its geological origin.
Simple Tests for Crystal Genuineness
Since the cold test is unreliable, a more effective method for the average buyer is a detailed visual inspection. This requires checking for tell-tale signs of artificial manufacturing rather than relying on temperature.
Checking for Internal Bubbles
One of the most obvious indicators of a glass or resin fake is the presence of perfectly round, internal air bubbles. These bubbles are trapped during the cooling process of a molten material. Genuine crystals form slowly under immense pressure and do not contain air bubbles. Instead, they feature natural inclusions, fractures, or mineral veins that often appear needle-like or irregular.
Hardness Test
Another practical test is to assess the crystal’s hardness, relating it to the Mohs scale of mineral hardness. Genuine quartz, for example, has a hardness of 7, meaning it cannot be scratched by common objects like a copper penny or a steel knife. A fake made of plastic or resin will likely scratch easily. This test should only be performed on an inconspicuous area or a non-valuable piece.
Density and Heft
You can also assess the density of the stone, often referred to as “heft.” Authentic minerals are generally denser than materials like plastic or resin. This density causes them to feel substantially heavier than expected for their size, providing a quick, tactile clue about the material composition.
Optical Properties
Finally, observing the way light passes through the stone can be revealing. Many genuine crystals exhibit birefringence or double refraction, which causes a slight visual distortion when looking through the stone. This optical property is absent in amorphous materials like glass, which only show single refraction.