The beauty of crystals attracts many collectors as well as people who use them for various purposes in healing and spirituality. These specimens of "frozen light" have different attributes that make them react in different ways to natural or electric light. Light is reflected and refracted on numerous forms of rock crystals from the shiny ores to the clear quartz families. Any polished rocks may reflect some light, but the quality found in most clear crystals that appeals to collectors is how light comes through the crystal itself, or how rainbows seem to form when viewing it from different angles. Certain crystals also glow under ultraviolet lights.
Quartz comes in many forms, and some of the most beautiful are ultraclear quartz, smoky quartz, rose quartz and amethyst. These can grow in clusters, or you may find a large one that has broken off from its matrix. Hold a quartz crystal up to a light source to view the clarity of the crystal. Look for imperfections --or phantoms -- that catch the light and redirect it in various ways. Moss quartz and rutilated quartz often contain many surfaces inside the crystal itself which reflect light. Amethyst in tight clusters creates a sparkling effect when light bounces off it.
Raw crystals of certain mineral ores reflect light in a more obvious manner: they shine. Whether or not an ore will reflect light is determined by its crystallinity and basic composition. The most reflective minerals are pyrite, copper, galena and silver. Galena is the crystalline raw form of lead, and its cubic shape reflects light easily. Pyrite, or fool's gold, is highly reflective on its many golden or silvery surfaces, especially in octahedron form. These metallic minerals appeal to collectors for a number of reasons, among them their weight, structure and reflective qualities.
Some crystals fall into the fluorescent category. Their light either reflects under normal light in a highly luminous manner, or it reflects primarily when viewed in ultraviolet light. Miners and rock hounds sometimes take UV light into caves or mines solely to look for such crystals. Blue, green and purple fluorite have fluorescent properties. Calcite, sodalite, corundum, karpatite, willemite, smithsonite, sodalite, apatite and tugtupite can be included in this group, but you will have to look at these in various light conditions as well as under UV light to appreciate their beauty.
Tourmaline, celestite, apophyllite, aventurine, and citrine are other highly reflective crystals. Some of these come in stunning clusters that radiate light in all directions. Tourmaline is commonly green or pink; it is known as the "watermelon" variety when the two mix. Celestite is bright blue to bluish white. Apophyllite can be greyish or bluish grey. Citrine is an orangey gold. Many of these can be found in extremely tiny clusters of crystals, or in larger sizes on gigantic chunks of rock or geodes.