Rutile

By: Ellie, Alex, April

Mineral Name: Rutile

Chemical Composition: TiO2- Titanium Dioxide

Color: Dark red, brownish-red, orange-red, mustard yellow

Streak: White to light brown

Hardness: 6-6.5

Cleavage/Fracture: It’s cleavage is in 2 directions and it’s fracture is conchoidal

Crystal Form: Rutile forms very thin needles and can vary in size depending on how much room it has when it forms in other minerals. Rutile has a prismatic crystal form that can be long, straight and slender (1). Rutile is also known for twinning. Rutile twinning can form sixlings (six crystals joined at the base), eightlings (six crystals joined at the base), knee-shaped twins and v-shaped twins (1). Capillary needles can form in a snowflake shape and, when the needle groups are more dense, they form in a star shape (1).

Luster: Adamantine and sub-metallic

Special Features: Rutile is commonly found as an inclusion in quartz, where it can form as spindles within the mineral, creating what is known as rutilated quartz. These inclusions can range from densely packed to sparse, crisscrossing to parallel, and each has a completely unique makeup of rutile (7). Due to the unique formation of rutilated quartz it is very easy to identify from other minerals with the exception of rutilated topaz. Rutilated topaz is a misnomer as the inclusions are composed of limonite rather than rutile but has very similar features to rutilated quartz besides having greater hardness (7).

Varieties: The varieties of rutile include struvite, sagenite, rutilated quartz, venus hairston, and ilmenorutile. Struvite is a tantalum-bearing form of rutile (1). Sagenite is a microcrystalline quartz stone that contains needle-like crystals of rutile (1). Rutilated quartz is quartz with inclusions of gold and yellow needle-looking forms of rutile. Venus Hairstone is a variety that is just densely packed groups of rutile that look almost hair-like (1). Ilmenorutile is a variety that contains niobium (1).

Mineral Group: Rutile belongs to the oxides and simple oxides group. Oxides are composed of multiple metallic elements that are combined with water, oxygen or hydroxyl and can be either extremely hard or soft. Simple oxides are metallic elements only combined with oxygen (1).

Environment: Rutile is found as an accessory mineral in intrusive igneous and metamorphic rocks and as a replacement mineral of hydrothermal veins. Hydrothermal veins form by water activity when heated fluids distribute throughout a rock and carry specific elements within the water (1). These waters dissolve mineral materials and redeposit new minerals in their place. Rutile can be found along beaches or areas of dense ore-mineral sands. These types of sands are known as “heavy mineral sands” and are found mostly in shallow water or in areas where the sea level was once higher (8). These sediments are mined, processed, and placed back in their original terrain. The process includes removing the large mineral grains while the lighter sediments are returned (8).

Associated Rock types: Rutile is often found in metamorphic rocks such as ecoglite, adinole, gneiss, and schist and igneous rocks such as lamproite and krageroite (1; 3).

Occurrence in North America: Rutile can be commonly found in sand because of its mineral properties and can be washed up onto the coastal lines in North America “where they are sorted and concentrated according to their density by wave and current action” (5). Rutile can also be found in mountainous alpine environments in states such as Georgia, North Carolina, Pennsylvania, Arkansas, and Champion Mine and White Mountains in California (1).

Economic Uses: Rutile is a source of titanium dioxide pigment and is commonly used for producing paints, plastics, paper products, and sunscreens as a whitener (4). To be used, the rutile must be finely pulverized and all impurities removed through processing, leaving a titanium oxide powder that is a vibrant white (8). At this point, the powder can be placed in a liquid to suspend the rutile which serves as a carrier in the application of paint; once applied the liquid will evaporate and the titanium oxide will remain (8). Titanium dioxide is nontoxic and chemically stable which allows it to be used in a wide variety of products (8).

Rutile is also used as a gemstone, though it’s creation through the Verneuil Process is now preferable to the use of natural crystals. In nature, rutile is a common inclusion in other minerals such as quartz, corundum (rubies and sapphires), and garnet, creating novelty gems with variations in the needles produced by the rutile (8). In some gems the light reflected through the network of fine rutile needles creates a star pattern known as an “asterism”(8). Other gem specimens with rutile inclusions may create a “chatoyance”, where a line of light on the gem’s surface produces a feature that looks like a cat’s eye; due to this distinct characteristic, it is often referred to as a “cat’s eye”(8). Synthetic rutile is most commonly used today instead of mining for natural rutile deposits. The Verneuil Process -also known as the flame fusion process- was first developed in 1902 by French chemist Auguste Verneuil for the processing of ground alumina into boule (9). The Verneuil Process was used to produce synthetic rutile in 1948 because natural rutile is dark in color while synthetic rutile can be manipulated to produce any shade of pigment desired (9).

Industrial Uses: When crushed rutile becomes a white powder that can be used to create white pigment in products such as refractory ceramics and a main component in the production of titanium metal (5). Titanium is a metal that is resistant to corrosion, which makes it a popular material in the production of jewelry, prosthetics, bicycle frames, scissors, surgical instruments, aircraft equipment and many other products (9). The titanium dioxide pigments produced from rutile are used to make white color in plastics and high-brightness printer paper (5). Being both non-toxic and chemically stable, rutile (as titanium dioxide) is a common pigmenting ingredient in food, cosmetics, toothpastes, pharmaceutical products and other consumer items (5).

First Notable Identification: Rutile’s name was first introduced by Abraham Gottolob Werner, a German geologist in 1800, the name comes from the Latin rutilus meaning “reddish” (3). At this time the mineral was already discovered and known under other names, such as “red schorl” and other names became different varieties observed of the mineral (3). It was first described by I. von Born in his 1772 catalog of minerals in Murán, Slovakia, as “Basaltes crystallisatus ruber” meaning “red crystalline schorl” at the time of its description the Latin Basaltes was used to describe both basalt columns and schorl (3).

How We Identified It: Rutile can be identified due to its unique needle-like crystal formation. Asterisms are formed inside the crystal that when you shine a through it, “stars” are reflected. It has multiple unique crystal forms as well as several telltale colors, styles, and associations. Rutile can range from mirror-like metallic-looking crystals, to dark reddish sub-metallic crystals, to bright golden-yellow needles. Even the opaque metallic-looking forms are somewhat translucent on edge under backlighting, with a dark red translucent tinge (1).

Don’t Confuse It With: Cassiterite! While they may look alike, cassiterite is heavier and the crystals are not as shiny as rutile. Schorl is similar as well, but is harder and has less of a red tint to it.



Bibliography:

  1. “Rutile: The Titanium Mineral Rutile Information and Pictures.” Rutile: The Titanium Mineral Rutile Information and Pictures, www.minerals.net/mineral/rutile.aspx.

  2. “Rutile.” Minerals Education Coalition, mineralseducationcoalition.org/minerals-database/rutile/.

  3. “Rutile.” Rutile: Mineral Information, Data and Localities., www.mindat.org/min-3486.html.

  4. “Rutile Mining Process: Equipment: Flow: Cases - JXSC Mining.” Equipment | Flow | Cases - JXSC Mining, 27 Nov. 2019, www.jxscmining.com/mineral-processing-plants/rutile-mining-process/.

  5. “Rutile.” Geology, geology.com/minerals/rutile.shtml.

  6. “Rutile” : Associated Rock Types, Rutile in Petrology https://www.mindat.org/min-3486.html#autoanchor22

  7. “Rutilated Quartz: The Gemstone Rutilated Quartz Information and Pictures.” Rutilated Quartz: The Gemstone Rutilated Quartz Information and Pictures, www.minerals.net/gemstone/rutilated_quartz_gemstone.aspx.

  8. King, Hobart. “Rutile.” Geology, Geoscience News and Information, geology.com/minerals/rutile.shtml.

  9. The Editors of Encyclopaedia Britannica. “Verneuil Process.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 22 Oct. 2013, www.britannica.com/topic/Verneuil-process.

  10. King, Hobart. “Uses of Titanium Metal and Titanium Dioxide.” Geology, geology.com/articles/titanium/.