Titanite

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Titanite (Sphene)
Titanite crystals on Amphibole - Ochtendung, Eifel, Germany.jpg
Titanite crystals on amphibole (image width 2 mm)
General
Category Nesosilicate
Formula
(repeating unit)
CaTiSiO5
IMA symbol Ttn [1]
Strunz classification 9.AG.15
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H–M symbol)
Space group P21/a
Unit cell a = 7.057  Å, b = 8.707 Å
c = 6.555 Å; β = 113.81°; Z = 4
Identification
ColourReddish brown, brown, gray, black, yellow, green, or red, colourless
Crystal habit Flattened wedge-shaped crystals, also massive
Twinning Contact and penetration on {100}, lamellar on {221}
Cleavage Distinct on [110], parting on {221}
Fracture Sub-conchoidal
Mohs scale hardness5–5.5
Luster Sub-adamantine tending to slightly resinous
Streak Reddish white
Diaphaneity Translucent to transparent
Specific gravity 3.48–3.60
Optical propertiesBiaxial (+); very high relief
Refractive index nα = 1.843–1.950
nβ = 1.870–2.034
nγ = 1.943–2.110
Birefringence δ = 0.100–0.160
Pleochroism Strong: X = nearly colorless; Y = yellow to green; Z = red to yellow-orange
2V angle 17–40° (measured)
Dispersion r > v strong
Other characteristics Radioactive.svg Radioactive – may be metamict
References [2] [3] [4] [5]
Titanite crystal model Titanite01.gif
Titanite crystal model

Titanite, or sphene (from Ancient Greek σφηνώ (sphēnṓ) 'wedge'), [5] is a calcium titanium nesosilicate mineral, Ca Ti Si O 5. Trace impurities of iron and aluminium are typically present. Also commonly present are rare earth metals including cerium and yttrium; calcium may be partly replaced by thorium. [6]

Contents

Nomenclature

The International Mineralogical Association Commission on New Minerals and Mineral Names (CNMMN) adopted the name titanite and "discredited" the name sphene [7] as of 1982, [8] although commonly papers and books initially identify the mineral using both names. [9] [10] Sphene was the most commonly used name until the IMA decision, although both were well known. [5] Some authorities [11] think it is less confusing as the word is used to describe any chemical or crystal with oxidized titanium such as the rare earth titanate pyrochlores series [12] and many of the minerals with the perovskite structure. [13] The name sphene continues to be publishable in peer-reviewed scientific literature, e.g. a paper by Hayden et al. was published in early 2008 in the journal Contributions to Mineralogy and Petrology. [11] Sphene persists as the informal name for titanite gemstones.

Physical properties

Green titanite crystal cluster from the Tormiq Valley, Haramosh Mountains, Pakistan Titanite - Tormiq valley, Haramosh Mts, Pakistan.jpg
Green titanite crystal cluster from the Tormiq Valley, Haramosh Mountains, Pakistan

Titanite, which is named for its titanium content, occurs as translucent to transparent, reddish brown, gray, yellow, green, or red monoclinic crystals. These crystals are typically sphenoid in habit and are often twinned. Possessing a subadamantine tending to slightly resinous luster, titanite has a hardness of 5.5 and a weak cleavage. Its specific gravity varies between 3.52 and 3.54. Titanite's refractive index is 1.885–1.990 to 1.915–2.050 with a strong birefringence of 0.105 to 0.135 (biaxial positive); under the microscope this leads to a distinctive high relief which combined with the common yellow-brown colour and lozenge-shape cross-section makes the mineral easy to identify. Transparent specimens are noted for their strong trichroism, the three colours presented being dependent on body colour. Owing to the quenching effect of iron, sphene exhibits no fluorescence under ultraviolet light. Some titanite has been found to be metamict, in consequence of structural damage due to radioactive decomposition of the often significant thorium content. When viewed in thin section with a petrographic microscope, pleochroic halos can be observed in minerals surrounding a titanite crystal.

Occurrence

Titanite occurs as a common accessory mineral in intermediate and felsic igneous rocks and associated pegmatites. It also occurs in metamorphic rocks such as gneiss and schists and skarns. [2] Source localities include: Pakistan; Italy; Russia; China; Brazil; Tujetsch, St. Gothard, Switzerland; [5] Madagascar; Tyrol, Austria; Renfrew County, Ontario, Canada; Sanford, Maine, Gouverneur, Diana, Rossie, Fine, Pitcairn, Brewster, New York [5] and California in the US.

Uses

Titanite is a source of titanium dioxide, TiO2, used in pigments.

As a gemstone, titanite is usually some shade of chartreuse, but can be brown or black. Hue depends on iron (Fe) content, with low Fe content causing green and yellow colours, and high Fe content causing brown or black hues. Zoning is typical in titanite. It is prized for its exceptional dispersive power (0.051, B to G interval) which exceeds that of diamond. [14] Jewelry use of titanite is limited, both because the stone is uncommon in gem quality and is relatively soft.

Titanite can also be used as a U-Pb geochronometer, specifically in metamorphic terranes.

Related Research Articles

<span class="mw-page-title-main">Spinel</span> Mineral or gemstone

Spinel is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula MgAl
2
O
4
in the cubic crystal system. Its name comes from the Latin word spinella, a diminutive form of spine, in reference to its pointed crystals.

<span class="mw-page-title-main">Zircon</span> Zirconium silicate, a mineral belonging to the group of nesosilicates

Zircon is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is ZrSiO4. An empirical formula showing some of the range of substitution in zircon is (Zr1–y, REEy)(SiO4)1–x(OH)4x–y. Zircon precipitates from silicate melts and has relatively high concentrations of high field strength incompatible elements. For example, hafnium is almost always present in quantities ranging from 1 to 4%. The crystal structure of zircon is tetragonal crystal system. The natural color of zircon varies between colorless, yellow-golden, red, brown, blue, and green.

<span class="mw-page-title-main">Baddeleyite</span>

Baddeleyite is a rare zirconium oxide mineral (ZrO2 or zirconia), occurring in a variety of monoclinic prismatic crystal forms. It is transparent to translucent, has high indices of refraction, and ranges from colorless to yellow, green, and dark brown. See etymology below.

<span class="mw-page-title-main">Axinite</span>

Axinite is a brown to violet-brown, or reddish-brown bladed group of minerals composed of calcium aluminium boro-silicate, (Ca,Fe,Mn)3Al2BO3Si4O12OH. Axinite is pyroelectric and piezoelectric.

<span class="mw-page-title-main">Augite</span> Common rock-forming pyroxene mineral

Augite, also known as Augurite, is a common rock-forming pyroxene mineral with formula (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6. The crystals are monoclinic and prismatic. Augite has two prominent cleavages, meeting at angles near 90 degrees.

<span class="mw-page-title-main">Zoisite</span> Sorosilicate mineral

Zoisite, first known as saualpite, after its type locality, is a calcium aluminum hydroxy sorosilicate belonging to the epidote group of minerals. Its chemical formula is Ca2Al3(SiO4)(Si2O7)O(OH).

<span class="mw-page-title-main">Astrophyllite</span> Hydrous potassium iron titanium silicate mineral

Astrophyllite is a very rare, brown to golden-yellow hydrous potassium iron titanium silicate mineral. Belonging to the astrophyllite group, astrophyllite may be classed either as an inosilicate, phyllosilicate, or an intermediate between the two. It forms an isomorphous series with kupletskite, to which it is visually identical and often intimately associated. Astrophyllite is of interest primarily to scientists and collectors.

<span class="mw-page-title-main">Thorite</span> Nesosilicate mineral

Thorite, (Th,U)SiO4, is a rare nesosilicate of thorium that crystallizes in the tetragonal system and is isomorphous with zircon and hafnon. It is the most common mineral of thorium and is nearly always strongly radioactive. Thorite was discovered in 1828 on the island of Løvøya, Norway, by the vicar and mineralogist, Hans Morten Thrane Esmark. First specimens of Thorite were sent to his father, Jens Esmark, who was a professor of mineralogy and geology. It was named in 1829 to reflect its thorium content.

<span class="mw-page-title-main">Xenotime</span> Phosphate mineral

Xenotime is a rare-earth phosphate mineral, the major component of which is yttrium orthophosphate (YPO4). It forms a solid solution series with chernovite-(Y) (YAsO4) and therefore may contain trace impurities of arsenic, as well as silicon dioxide and calcium. The rare-earth elements dysprosium, erbium, terbium and ytterbium, as well as metal elements such as thorium and uranium (all replacing yttrium) are the expressive secondary components of xenotime. Due to uranium and thorium impurities, some xenotime specimens may be weakly to strongly radioactive. Lithiophyllite, monazite and purpurite are sometimes grouped with xenotime in the informal "anhydrous phosphates" group. Xenotime is used chiefly as a source of yttrium and heavy lanthanide metals (dysprosium, ytterbium, erbium and gadolinium). Occasionally, gemstones are also cut from the finest xenotime crystals.

<span class="mw-page-title-main">Spessartine</span> Nesosilicate, manganese aluminium garnet species

Spessartine is a nesosilicate, manganese aluminium garnet species, Mn2+3Al2(SiO4)3. This mineral is sometimes mistakenly referred to as spessartite.

<span class="mw-page-title-main">Chondrodite</span>

Chondrodite is a nesosilicate mineral with formula (Mg,Fe)
5
(SiO
4
)
2
(F,OH,O)
2
. Although it is a fairly rare mineral, it is the most frequently encountered member of the humite group of minerals. It is formed in hydrothermal deposits from locally metamorphosed dolomite. It is also found associated with skarn and serpentinite. It was discovered in 1817 at Pargas in Finland, and named from the Greek for "granule", which is a common habit for this mineral.

<span class="mw-page-title-main">Lawsonite</span>

Lawsonite is a hydrous calcium aluminium sorosilicate mineral with formula CaAl2Si2O7(OH)2·H2O. Lawsonite crystallizes in the orthorhombic system in prismatic, often tabular crystals. Crystal twinning is common. It forms transparent to translucent colorless, white, pink, and bluish to pinkish grey glassy to greasy crystals. Refractive indices are nα = 1.665, nβ = 1.672 – 1.676, and nγ = 1.684 – 1.686. It is typically almost colorless in thin section, but some lawsonite is pleochroic from colorless to pale yellow to pale blue, depending on orientation. The mineral has a Mohs hardness of 7.5 and a specific gravity of 3.09. It has perfect cleavage in two directions and a brittle fracture.

<span class="mw-page-title-main">Microlite</span>

Microlite was once known as a pale-yellow, reddish-brown, or black isometric mineral composed of sodium calcium tantalum oxide with a small amount of fluorine. Its chemical formula is(Na,Ca)2Ta2O6(O,OH,F). Today it is a name of a group of oxide minerals of a similar stoichiometry having tantalum prevailing over titanium and niobium. The microlite group belongs to a large pyrochlore supergroup that occurs in pegmatites and constitutes an ore of tantalum. It has a Mohs hardness of 5.5 and a variable specific gravity of 4.2 to 6.4. It occurs as disseminated microscopic subtranslucent to opaque octahedral crystals with a refractive index of 2.0 to 2.2. Microlite is also called djalmaite, but both names are now obsolete.

<span class="mw-page-title-main">Lorenzenite</span> Sodium titanium silicate mineral

Lorenzenite is a rare sodium titanium silicate mineral with the formula Na2Ti2Si2O9 It is an orthorhombic mineral, variously found as colorless, grey, pinkish, or brown crystals.

<span class="mw-page-title-main">Cafetite</span>

Cafetite is a rare titanium oxide mineral with formula (Ca,Mg)(Fe,Al)
2
Ti
4
O
12
·4(H
2
O)
. It is named for its composition, Ca-Fe-Ti.

Schreyerite (V2Ti3O9), is a vanadium, titanium oxide mineral found in the Lasamba Hill, Kwale district in Coast Province, Kenya. It is polymorphous with kyzylkumite.

<span class="mw-page-title-main">Betafite</span> Mineral group

Betafite is a mineral group in the pyrochlore supergroup, with the chemical formula (Ca,U)2(Ti,Nb,Ta)2O6(OH). Betafite typically occurs as a primary mineral in granite pegmatites, rarely in carbonatites. Originally defined by the B-site atom Ti, the development of new nomenclature for mineral names led to modernization of the system for nomenclature of pyrochlore and betafite in order to further rationalize the naming process of this grouping of minerals. Only two of the mineral species that were formerly recognized as betafite are presently retained. They are oxyuranobetafite and oxycalciobetafite. The term betafite is now a synonym or varietal group name under the pyrochlore super group.

<span class="mw-page-title-main">Perovskite</span> Oxide mineral

Perovskite (pronunciation: ) is a calcium titanium oxide mineral composed of calcium titanate (chemical formula CaTiO3). Its name is also applied to the class of compounds which have the same type of crystal structure as CaTiO3, known as the perovskite structure, which has a general chemical formula A2+B4+(X2−)3. Many different cations can be embedded in this structure, allowing the development of diverse engineered materials.

Anzaite-(Ce) is a rare-earth element (REE) oxide mineral with the formula Ce4Fe2+Ti6O18(OH)2. An example of chemically related mineral is lucasite-(Ce), although it contains no iron. Cerium in anzaite-(Ce) is mainly substituted by neodymium, lanthanum, calcium and praseodymium. Titanium is substituted by niobium. Trace elements include thorium. The mineral is monoclinic, space group C2/m. Anzaite-(Ce) is hydrothermal mineral found in a carbonatite from the mineralogically prolific Kola Peninsula. The mineral name honors Anatoly N. Zaitsev, who is known for studies of carbonatites and REE.

References

  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. 1 2 "Titanite". Handbook of Mineralogy (PDF).
  3. Titanite Mineral Data, WebMineral.com
  4. Titanite, Mindat.org
  5. 1 2 3 4 5 Dana, James Dwight; Ford, William Ebenezer (1915). Dana's Manual of Mineralogy for the Student of Elementary Mineralogy, the Mining Engineer, the Geologist, the Prospector, the Collector, Etc (13 ed.). John Wiley & Sons, Inc. pp.  299–300. Retrieved 2009-07-06.
  6. Deer, W. A.; Howie, R. A.; Zussman, J. (1966). Introduction to the Rock-Forming Minerals. Longman. pp. 17–20. ISBN   0-582-44210-9.
  7. Nickel, Ernest H.; Nichols, Monte C. (2008-10-17). "IMA/CNMNC List of Mineral Names" (PDF). Material Data, Inc. p. 280. Retrieved 2009-03-14.
  8. Hey, M. H. (December 1982). "International Mineralogical Association: Commission on New Minerals and Mineral Names". Mineralogical Magazine. 46 (341): 513–514. Bibcode:1982MinM...46..513H. doi:10.1180/minmag.1982.046.341.25. S2CID   140202196.
  9. Wenk, Hans-Rudolf; Bulakh, Andrei (May 2004). Minerals: Their Constitution and Origin. New York, NY: Cambridge University Press. ISBN   978-0-521-52958-7.
  10. Nesse, William D. (August 2003). Introduction to Optical Mineralogy. New York, NY: Oxford University Press, USA. ISBN   978-0-19-514910-4.
  11. 1 2 Hayden, L. A.; Watson, E. B.; Wark, D. A. (2008). "A thermobarometer for sphene (titanite)". Contributions to Mineralogy and Petrology. 155 (4): 529–540. Bibcode:2008CoMP..155..529H. doi:10.1007/s00410-007-0256-y. S2CID   129085138.
  12. Helean, K. B.; Ushakov, S. V.; Brown, C. E.; Navrotsky, A.; Lian, J.; Ewing, R. C.; Farmer, J. M.; Boatner, L. A. (June 2004). "Formation enthalpies of rare earth titanate pyrochlores". Journal of Solid State Chemistry. 177 (6): 1858–1866. Bibcode:2004JSSCh.177.1858H. doi:10.1016/j.jssc.2004.01.009. S2CID   97381935.
  13. Freitas, G. F. G.; Nasar, R. S.; Cerqueira, M.; Melo, D. M. A.; Longo, E.; Varela, J. A. (October 2006). "Luminescence in semi-crystalline zirconium titanate doped with lanthanum". Materials Science and Engineering: A. 434 (1–2): 19–22. doi:10.1016/j.msea.2006.07.023.
  14. "Sphene (Titanite) Value, Price, and Jewelry Information". International Gem Society.