Rutile

Rutile
General
CategoryOxide minerals
Formula
(repeating unit)
TiO2
IMA symbolRt[1]
Strunz classification4.DB.05
Crystal systemTetragonal
Crystal classDitetragonal dipyramidal (4/mmm)
H-M symbol: (4/m 2/m 2/m)
Space groupP42/mnm
Unit cella = 4.5937 Å, c = 2.9587 Å; Z = 2
Identification
ColorBrown, reddish brown, blood red, red, brownish yellow, pale yellow, yellow, pale blue, violet, rarely grass-green, grayish black; black if high in Nb–Ta
Crystal habitAcicular to Prismatic crystals, elongated and striated parallel to [001]
TwinningCommon on {011}, or {031}; as contact twins with two, six, or eight individuals, cyclic, polysynthetic
Cleavage{110} good, {100} moderate, parting on {092} and {011}
FractureUneven to sub-conchoidal
Mohs scale hardness6.0–6.5
LusterAdamantine to metallic
StreakBright red to dark red
DiaphaneityOpaque, transparent in thin fragments
Specific gravity4.23 increasing with Nb–Ta content
Optical propertiesUniaxial (+)
Refractive indexnω = 2.613, nε = 2.909 (589 nm)
Birefringence0.296 (589 nm)
PleochroismWeak to distinct brownish red-green-yellow
DispersionStrong
FusibilityFusible in alkali carbonates
SolubilityInsoluble in acids
Common impuritiesFe, Nb, Ta
Other characteristicsStrongly anisotropic
References[2][3][4][5]

Rutile is an oxide mineral composed of titanium dioxide (TiO2), the most common natural form of TiO2. Rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite.

Rutile has one of the highest refractive indices at visible wavelengths of any known crystal and also exhibits a particularly large birefringence and high dispersion. Owing to these properties, it is useful for the manufacture of certain optical elements, especially polarization optics, for longer visible and infrared wavelengths up to about 4.5 micrometres. Natural rutile may contain up to 10% iron and significant amounts of niobium and tantalum.

Rutile derives its name from the Latin rutilus ('red'), in reference to the deep red color observed in some specimens when viewed by transmitted light. Rutile was first described in 1803 by Abraham Gottlob Werner using specimens obtained in Horcajuelo de la Sierra, Madrid (Spain),[6] which is consequently the type locality.

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Handbook of Mineralogy.
  3. ^ Webmineral data.
  4. ^ Mindat.org.
  5. ^ Klein, Cornelis and Cornelius S. Hurlbut, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York, pp. 304–05, ISBN 0-471-80580-7.
  6. ^ Calvo, Miguel (2009). Minerales y Minas de España. Vol. IV. Óxidos e hidróxidos (in Spanish). Madrid, Spain: Escuela Técnica Superior de Ingenieros de Minas de Madrid. Fundación Gómez Pardo. p. 237.