Rutile

Rutile is the most common natural form of titanium dioxide and an important ore of titanium. It crystallizes in the tetragonal system as slender prismatic crystals, often vertically striated, and frequently forms distinctive knee-shaped twins. Colors range from reddish-brown and blood-red to black and golden, with an adamantine to submetallic luster and a very high refractive index.

Rutile is best known to collectors as the fine golden, copper, or reddish needles that pierce quartz to create rutilated quartz, also called Venus hair or fléches d'amour ("arrows of love"). Radiating sprays are called sagenite.

Tiny oriented rutile inclusions are also responsible for the asterism (star effect) seen in star rubies and star sapphires.

Rutile forms across a wide range of geologic environments. It crystallizes in high-pressure and high-temperature metamorphic rocks such as eclogites, gneisses, and schists, and as an accessory mineral in granites and pegmatites.

It also grows as oriented needles inside quartz and corundum during their crystallization. Because rutile is hard and chemically durable, it survives weathering and concentrates in heavy-mineral beach and river sands, which are the main commercial source of titanium. Notable localities include Graves Mountain in Georgia (USA), the Alps, Brazil, Norway, and the titanium-rich sand deposits of Australia, India, and Sierra Leone.

Rutile crystals are slender, striated prisms, often reddish-brown to red with a brilliant adamantine to almost metallic luster and a pale brown to yellowish streak. Hardness is 6-6.5, and characteristic elbow (geniculated) twins are a strong clue.

As inclusions, golden to copper-red needles threading through clear quartz are unmistakable and define rutilated quartz. Look-alikes include cassiterite (denser, lighter streak) and brookite/anatase (the other TiO2 polymorphs, distinguished by crystal form). The combination of high luster, reddish color, and needle-like habit usually identifies rutile readily.

Rutile is a primary ore of titanium, supplying metal for lightweight, strong, corrosion-resistant alloys used in aerospace, medical implants, and marine equipment. Even more rutile is processed into titanium dioxide pigment, the brilliant white opacifier in paints, plastics, paper, sunscreen, and cosmetics.

Rutilated quartz is a popular gemstone, cut into cabochons, beads, and faceted stones that showcase the golden needles, and is valued metaphysically for energy and clarity. Synthetic rutile has been used as a diamond simulant because of its intense fire, though its softness limits jewelry use.