Pseudobrookit

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Pseudobrookit
Pseudobrookite block3 - Ochtendung, Eifel, Germany.jpg
Pseudobrookite crystal clearly orthorhombic and typical striations on the left side.
Size: 0.8 mm
General and classification
chemical formula [(Fe 3+ ) 2 Ti] O 5
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.CB.15 ( 8th edition : IV / C.24)
07.07.01.01
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-dipyramidal 2 / m 2 / m 2 / m
Space group Bbmm
Lattice parameters a  = 9.77  Å ; b  = 9.95 Å; c  = 3.72 Å
Formula units Z  = 4
Physical Properties
Mohs hardness 6th
Density (g / cm 3 ) 4.33 to 4.39
Cleavage clearly after {102}
Break ; Tenacity uneven to scalloped
colour red-brown, brownish-black
Line color reddish brown to yellowish brown
transparency opaque, translucent in thin layers
shine Metallic luster, diamond luster, fat luster
Crystal optics
Refractive indices n α  = 2.350
n β  = 2.390
n γ  = 2.420
Birefringence δ = 0.070
Optical character biaxial positive
Axis angle 2V = measured: 50 °; calculated: 80 °

Pseudobrookite is a rather rare mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the orthorhombic crystal system with the chemical composition [(Fe 3+ ) 2 Ti] O 5 and usually develops short to long prismatic crystals or radial, tufted mineral aggregates up to 7 cm in size and red-brown to brownish-black in color.


Etymology and history

Tabular, brown pseudobrookite

Pseudobrookite was found for the first time in 1878 on Magura Uroiului near Uroi (Arany) in the Romanian district of Hunedoara and described by Antal Koch (1843–1927), who named the mineral because of its similarity and risk of confusion with brookite after it with the Greek word addition ψευδ ~ for "wrong, fake, pretended ”.

classification

In the old systematics of minerals according to Strunz (8th edition) the pseudobrookit belonged to the department of "oxides with the molar ratio metal: oxygen = 2: 3", where it forms a separate, unnamed group together with armalcolite and pseudorutile .

Since the 9th edition of Strunz's mineral systematics , the departments of the oxide / hydroxide class have been subdivided more precisely according to the size of the cations and some have been renamed. Pseudobrookite is now in the subdivision of "Oxides with the molar ratio metal: oxygen = 2: 3, 3: 5 and comparable and medium-sized cations", where it forms the unnamed group 4.CB.15 together with armalcolite and mongshanite .

The systematics of minerals according to Dana , which is common in the English-speaking world , also sorts the pseudobrookit into the class of oxides and hydroxides, but there into the division of " multiple oxides with different formulas ", where it is used together with armalcolite and previously only with the system no . IMA2000-016-equipped mineral forms the unnamed subdivision 7.7.1 .

Education and Locations

Pseudobrookite forms as a pneumatolytic decomposition product of ilmenite in titanium-rich andesites , rhyolites , basalts and other volcanic rocks . There he appears in various parageneses in addition to ilmenite, among other things, with apatite , beryl , bixbyite , various mica , hematite , cassiterite , magnetite , quartz , sanidine , spessartine , topaz , tridymite .

So far, pseudobrookit has been found at around 130 sites (as of 2010), including Algeria , Australia , Brazil , Bulgaria , Chile , Germany , France , Greece , Italy , Japan , Mexico , New Zealand , Norway , Austria , Romania , Russia , Slovakia , Spain , South Africa , Tanzania , Czech Republic , Hungary , the United Kingdom (Great Britain) and the United States (USA).

morphology

View of the board surface (100) with typical stripes

In general, pseudobrookite crystals show a short to long prismatic habit with a preferred growth direction along the b and c axes ([010] and [001]), which leads to the formation of tabular crystals according to {100}, the faces of which have a characteristic parallel stripe have to the c-axis.

Crystal structure

Crystal structure of pseudobrookite
view of the a-axis
white = iron, blue = titanium, red = oxygen

Pseudobrookit crystallizes orthorhombically in the space group Bbmm with the lattice parameters a  = 9.77  Å ; b  = 9.95 Å and c  = 3.72 Å as well as four formula units per unit cell .

See also

Individual evidence

  1. ↑ Webmineral - Pseudobrookite (English)
  2. ^ A b Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 194 .
  3. ↑ a b Handbook of Mineralogy - Pseudobrookite (English, PDF 69.5 kB)
  4. ↑ a b c Pseudobrookite at mindat.org (engl.)
  5. ↑ IMA / CNMNC List of Mineral Names - Pseudobrookite (English, PDF 1.8 MB; p. 233)
  6. ↑ Mindat - Localities for pseudobrookites
  7. ^ Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 194 .

literature

Web links

Commons : Pseudobrookite  - collection of images, videos and audio files