Titanite
Titanite, also called sphene, is a commonly occurring mineral from the mineral class of " Silicate and germanate ". It crystallizes in the monoclinic crystal system with the chemical composition CaTi [O | SiO4 ] and usually develops tabular, wedge-shaped tapered crystals and twins, but also granular to massive aggregates.
Special Features
Pure titanite is colorless. However, it may be caused by foreign admixtures of yellow, green, brown or gray to black in color.
The mineral is sensitive to acids ( complete solubility in sulfuric acid), alkalis and heat sources. Depending on the locality may by foreign admixtures of uranium, thorium or radium be weakly radioactive and a specific activity of about 82 Bq / g (compared to natural potassium 31.2 Bq / g).
Before the blowpipe titanite melts at the edges to dark glass.
Etymology and history
Was first found in 1795 in the titanite Hauzenberger graphite mines in the Bavarian Forest and described by Martin Heinrich Klaproth, who named the mineral after its titanium content.
The synonym sphene ( altgr. σφήν sphene " wedge" ) received titanite due to its often wedge-shaped crystal forms.
Classification
In the now outdated nomenclature of minerals by Strunz ( 8th edition ) is one of the titanite nor the general department of the " island silicates with tetrahedral foreign anions ( Neso - Subsilikate ) " without further subdivisions, where he along with malayaite, Trimounsit - (Y) and Vanadomalayait forms its own group.
The revision of the Strunz'schen Mineral classification in its 9th edition, this department was precisely divided by the coordination of the involved cations and the mineral is now, only with malayaite and Vanadomalayait own group forming, in the subsection " island silicates with additional anions; Cations in most cases and > coordination ".
The commonly used in English-speaking classification of minerals according to Dana assigns the titanite also in the class of silicates, there, however, in the department of " island silicates: SiO4 Groups and O, OH, F, and H 2 O with cations in and / or > Coordination " where it forms as Leitmineral together with malayaite and Vanadomalayait the " Titanitgruppe ".
Petrology and Geochemistry
Titanite is a typical mineral of rocks of the greenschist facies. The stability of titania depends primarily on the oxygen fugacity. Another important factor is the incorporation of Al. Titanite is stable according to Ernst & Liu (1996 ) at pressures up to 1.2 GPa and temperatures up to 800 ° C. At higher temperatures, ilmenite is stable at higher pressures rutile.
Education and Locations
Titanite formed either directly by magmatic or indirectly by metamorphic processes in pegmatites.
Worldwide, titanite so far (as of 2010) are detected at approximately 2,900 localities. Rich deposits with three or more localities are in Argentina, Australia, Bolivia, Brazil, Bulgaria, Chile, China, Germany, Finland, France, Greece, India, Ireland, Italy, Japan, Cameroon, Canada, Kazakhstan, Kyrgyzstan, Cuba, Madagascar, Malawi, Morocco, Mexico, Mongolia, Namibia, North Korea, Norway, Austria, Pakistan, Portugal, Romania, Russia, Sweden, Switzerland, Slovakia, Spain, Sri Lanka, South Africa, South Korea, Tanzania, the Czech Republic, Ukraine, the United Kingdom ( UK) and in the United States of America ( USA)
Attractive, collectible Titanite with sometimes up to 18 cm large crystals are, however, mainly from Austria, Russia, Switzerland, Canada and the United States. A famous historical discovery site in Germany is the reason Plauensche between Dresden and Freital. In the upcoming multi monzonite the famous Titanitspiegel were found.
Crystal structure
Titanite crystallizes in the monoclinic space group P21 / a with the values determined in several measurements of 2000, the average lattice parameters a = 7.02 Å; b = 8.70 Å; c = 6.52 Å and β = 113.62 °, and four formula units per unit cell.
Use
As a raw material
Titanite is used at local accumulation as a raw material for the production of titanium dioxide ( TiO2). However, the already naturally occurring titanium dioxide rutile, anatase and brookite are preferred.
As a gemstone
Clear varieties are processed into semi-precious stones and is used in facet cut primarily as a diamond substitute. However, the mineral is not easy to work with because of its sensitivity to acids, alkalis and heat sources.