Crystals are solid materials with atoms, molecules, or ions arranged in a highly ordered, repeating pattern. These formations occur naturally over long geological periods under specific conditions. Blue crystals are a captivating segment of these natural formations, distinguished by their unique coloration.
How Crystals Get Their Blue Color
The vibrant blue hues seen in various crystals arise from several distinct scientific mechanisms. One common cause is the presence of specific trace elements within the crystal’s atomic structure. For instance, the captivating blue of sapphire, a variety of corundum, often results from minute amounts of iron and titanium impurities that substitute for aluminum atoms in the crystal lattice. These elements absorb certain wavelengths of light, allowing only the blue light to be transmitted or reflected, creating the perceived color.
Another mechanism involves defects within the crystal lattice, which are irregularities in the otherwise perfect atomic arrangement. These structural imperfections, sometimes caused by radiation or plastic deformation, can trap electrons, creating “color centers” that absorb light at specific wavelengths, leading to a blue appearance. For example, some blue diamonds get their color from boron impurities creating such defects, or specific types of blue topaz acquire their color through irradiation which creates color centers.
Beyond impurities and defects, some crystals exhibit blue color due to the physical phenomenon of light scattering. This occurs when light interacts with very fine particles or inclusions within the crystal structure. Blue light, having shorter wavelengths, is scattered more efficiently than other colors, similar to how the Earth’s atmosphere appears blue. While less common as a primary cause for intense blue in crystals, this effect can contribute to subtle blue tinges or opalescence in certain minerals.
Exploring Common Blue Crystals
Sapphire is a blue crystal primarily composed of aluminum oxide. Its deep blue color results from iron and titanium impurities. Ranking 9 on the Mohs scale of hardness, sapphires are highly durable and popular for various jewelry applications.
Lapis Lazuli is a metamorphic rock, recognized by its distinctive deep blue color with golden flecks of pyrite. Its intense blue hue originates from sulfur within the lazurite mineral. Softer than sapphire, typically 5 to 5.5 on the Mohs scale, Lapis Lazuli has been valued for carvings and ornamental objects for centuries.
Aquamarine, a blue-green variety of beryl, exhibits colors from pale to deep blue, often with a hint of green. Its coloration is attributed to iron impurities. With a hardness of 7.5 to 8 on the Mohs scale, aquamarine is durable enough for various jewelry uses.
Turquoise is an opaque, blue-to-green mineral, with its characteristic sky-blue color stemming from copper. Iron impurities can shift its hue towards green. Turquoise typically ranges from 5 to 6 on the Mohs scale, making it suitable for cabochons and carvings.
Blue Topaz, often pale blue, is a silicate mineral frequently heat-treated and irradiated to achieve more intense shades. Topaz has a hardness of 8 on the Mohs scale and is widely used in jewelry due to its brilliance.
Tanzanite is a rare blue-violet variety of zoisite, found exclusively in northern Tanzania. Its striking blue-violet pleochroism, displaying different colors from various angles, is due to vanadium impurities. Tanzanite is relatively soft, ranging from 6 to 7 on the Mohs scale, requiring careful handling in jewelry.
Distinguishing Natural and Lab-Created Blue Crystals
Many popular blue crystals have lab-created counterparts that are chemically and structurally identical to their natural versions. These synthetic crystals are grown in controlled environments, mimicking the geological processes that form natural crystals but over a much shorter timeframe. Common methods include hydrothermal growth, which uses high temperature and pressure to dissolve and recrystallize minerals in an aqueous solution, and the Verneuil process (also known as flame fusion), which involves melting powdered materials like aluminum oxide and allowing them to crystallize drop by drop as they cool.
Lab-created blue crystals, such as synthetic sapphires or spinels, possess the same chemical composition and physical properties, including hardness and optical characteristics, as their natural equivalents. However, they typically lack the natural inclusions, irregular growth patterns, or slight color variations that gemologists use to identify natural stones. Microscopic examination often reveals distinct growth lines or gas bubbles indicative of laboratory synthesis. The primary reasons for producing lab-created options include reducing costs, increasing availability, and ensuring consistent quality and color. While visually similar, their origin impacts their market value and perceived rarity significantly.