Quartz is one of the most abundant minerals on the Earth's surface. It is silica-based and forms rhombohedral, prismatic crystals in a variety of types, sizes, and colors. Several major varieties of quartz are gemstones, including amethyst, citrine, jasper and carnelian. Rutilated quartz is perhaps the most unusual variety of this mineral.
According to the Smithsonian book "Rock and Gem," "[t]aking its name from the Latin rutilis, 'red' or 'glowing', rutile is a form of titanium oxide." It is typically red, brown or almost black in color, and grows in slender, prismatic crystals with vertical striations. However, rutile can form within other stones, creating needle-shaped inclusions. In fact, rutile inclusions are the cause of asterism in star rubies and sapphires. Rutilated quartz is created when rutile forms within a quartz stone.
Rutilated quartz is unique because instead of red or black inclusions, in quartz the rutile inclusions are a beautiful, translucent, golden-yellow color. No two stones are alike. One stone may have only a few inclusions; another may have so many that the stone appears opaque. Also, the needle-shaped inclusions may form in sprays or in a random fashion. Though quartz is rated 7 on the Mohs hardness scale, rutile is rated 6 to 6.5.
Because quartz is such an abundant mineral, it may be found all over the world. Rutilated quartz stones have been discovered in Australia, Brazil, Madagascar, Sweden, Italy, France and Brazil. Rutilated quartz has also been found in the Eastern United States, including in Pennsylvania, North Carolina and Virginia. Mountain ranges typically have large quantities of quartz.
As a rule of thumb, gemstones are more highly valued if they have few or no inclusions. Rutilated quartz is unique because it is more highly valued for its inclusions. Also called Venus' hairstone, this gem has been regarded as an ornamental stone for centuries and used to create unusual jewelry. Some believe rutilated quartz has the power to aid sleep and depression, to slow aging and to enhance originality.
Rutile is not the only mineral that forms inclusions within quartz stones. Rutilated quartz is sometimes confused with tourmalinated quartz. Tourmalinated (or tourmalated) quartz is a quartz stone with needle-like inclusions of black or dark green tourmaline embedded within it. This gemstone, like rutilated quartz, may be used in ornamental pieces or jewelry, whether faceted or as a cabochon. Some believe this stone, when rubbed, brings luck.