Brushite

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Brushite
Brushite, Montmorillonite-445846.jpg
Tiny, white brushite crystals on gray, coarse montmorillonite (field of view 2 cm)
General and classification
other names

Epiglaubite

chemical formula
  • Ca [PO 3 (OH)] • 2H 2 O
  • CaH [PO 4 ] • 2H 2 O
Mineral class
(and possibly department)
Phosphates, arsenates and vanadates
System no. to Strunz
and to Dana
8.CJ.50 ( 8th edition : VII / C.25)
39.01.01.01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Room group (no.) A 2 / a (No. 15)
Lattice parameters a  = 6.24  Å ; b  = 15.18 Å; c  = 6.36 Å
β  = 125.4 °
Formula units Z  = 4
Physical Properties
Mohs hardness 2.5
Density (g / cm 3 ) measured: 2.328; calculated: 2.257
Cleavage completely according to {010} and {001}
colour colorless, white, light yellow
Line color White
transparency transparent to translucent
shine Glass luster, pearlescent luster on cleavage surfaces
Crystal optics
Refractive indices n α  = 1.539 to 1.540
n β  = 1.544 to 1.546
n γ  = 1.551 to 1.552
Birefringence δ = 0.012
Optical character biaxial positive
Axis angle 2V = measured: 59 to 87 °; calculated: 80 °
Other properties
Chemical behavior easily soluble in hydrochloric acid (HCl)
Special features piezoelectric

Brushite (also epiglaubite ) is a rarely occurring mineral from the mineral class of "phosphates, arsenates and vanadates". It crystallizes in the monoclinic crystal system with the chemical composition Ca [PO 3 (OH)] · 2H 2 O, is thus a water-containing , basic calcium - phosphate or the dihydrate of calcium hydrogenphosphate .

Brushite usually develops prismatic crystals with a needle-like or tabular habit up to about two centimeters in size. Uninjured surfaces have a glass-like sheen , whereas the cracked surfaces have a more mother-of-pearl shimmer . Brushite also rarely occurs in leafy or powdery-earthy, matt mineral aggregates . In its pure form, the mineral is colorless and transparent. However, due to multiple light refraction due to lattice construction defects or polycrystalline formation, it can also appear white and, due to foreign admixtures, take on a light yellow color, the transparency decreasing accordingly.

With a Mohs hardness of 2.5, brushite is one of the soft minerals that can be scratched with a copper coin more easily than the closest reference mineral calcite (3).

Etymology and history

The mineral was first discovered in guano on the island of Aves claimed by Venezuela (Spanish Isla de Aves , "bird island") and in 1856 by Charles Upham Shepard initially referred to as epiglaubite , but only incompletely described. A scientifically precise description followed in 1865 by Gideon Emmet Moore (1842–1895), who named the mineral after the American mineralogist George Jarvis Brush .

classification

Even in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , brushite belonged to the mineral class of "phosphates, arsenates and vanadates" and to the department of "water-containing phosphates without foreign anions ", where it was named after the "brushite- Group "with the system no. VII / C.25 and the other members Churchit- (Dy) , Churchit- (Nd) , Churchit- (Y) and Pharmacolite .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also assigns brushite to the category of “phosphates etc. without additional anions; with H 2 O “. However, this is further subdivided according to the relative size of the cations involved , so that the mineral can be found according to its composition in the sub-section "Only with large cations", where it can be found together with Ardealit , Churchit- (Nd), Churchit- (Y) and pharmacolite the "Churchit group" with the system no. 8.CJ.50 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns brushite to the class of "phosphates, arsenates and vanadates" and there in the department of "water-containing acidic phosphates, etc.". Here it can be found together with Pharmacolite in the unnamed group 39.01.01 within the subsection “ Hydrous acidic phosphates etc., A + [HXO 4 ] × x (H 2 O) ”.

Crystal structure

Brushite crystallizes monoclinically in the space group A 2 / a (space group no. 15) with the lattice parameters a  = 6.24  Å ; b  = 15.18 Å; c  = 6.36 Å and β = 125.4 ° and 4 formula units per unit cell .

properties

Brushite is piezoelectric , so, like the well-known quartz , it builds up an electrical voltage with changing, elastic deformation. It is easily soluble in hydrochloric acid (HCl).

Education and Locations

Brushite formed mostly in guano - deposits , but can also be part of urinary be as well as secondary occur formation on human and animal bones. Accompanying minerals include ardealite , gypsum , hydroxyapatite , tanarakite and variscite .

As a rare mineral formation, brushite could only be detected at a few sites, whereby so far (as of 2014) around 80 sites are known. In addition to its type locality , the island of Aves , the mineral was found in Venezuela in the "Cueva de San Sebastián" in the state of Aragua as well as in the "Cueva Ricardo Zuloaga" and the "Cuevo del Indio" in the state of Miranda .

In Germany, brushite was found on the Lüneburg Kalkberg in Lower Saxony, in the zinc smelter Birkengang (also Friedrich-Wilhelm-Hütte ) near Aachen and on the slag heaps of a copper smelter near Kall in North Rhine-Westphalia, near Schneeberg and in Pawel-Gang near Oberschlema in Saxony Erzgebirge and found in the pit "Jeremias Glück" ( fairy grottoes ) near Garnsdorf in Thuringia.

In Austria, the mineral is known mainly from Carinthia , where it is found on the "Kleinelend Glacier" (Kleinelend valley) and in rock samples from the Kaponig tunnel construction in the Mölltal in the Ankogel group and at some sites near Lanisch in the Hafner group belonging to Pöllatal . There is also a find at Türnitz in the Mostviertel and at the vineyard near Amstall in the Krems-Land district in Lower Austria, the Windischkopf bear cave near Tenneck (Werfen municipality) in Salzburg and the "Roßblei" (or Rossblei ) pit on the Eschach Alp in Obertal near the municipality of Rohrmoos-Untertal in Styria.

In Switzerland, brushite has so far only been found in the Burgdorf Church in the Bernese Emmental and in the Payerne Church in the Canton of Vaud, where it was found on human bones during excavations in 1968–1969 and in the 1950s.

Other locations include Algeria, Antarctica, Australia, the Bahamas, the British West Indies, Denmark, France, Italy, Japan, Canada, Kenya, Kiribati, Malaysia, Morocco, Mexico, Namibia, Puerto Rico, Réunion, Romania, Russia, Slovakia, Spain, South Africa, Hungary, the United Kingdom (UK) and the United States of America (USA).

Organic education

Brushite can be formed by precipitation from the urine in the urinary tract and thus lead to urinary stones . However, since brushite is very soluble, this mineral rarely occurs in urinary stones. Prerequisites are a high calcium content in the urine and a pH value between 6.5 and 6.8. Higher pH values ​​lead to the formation of (Ca 3 (PO 4 ) 2 ), with more acidic conditions the solubility increases sharply. In medical terms, brushite stones are among the hard stones that are relatively difficult to treat and can hardly be destroyed by extracorporeal shock wave lithotripsy . They also tend to recur quickly .

Brushite can also be involved in the formation of tartar .

From a dental perspective, brushite is important in the enamel etching technique for restorations. Enamel etching is usually done with phosphoric acid at a concentration of 35–37%. A concentration of less than 30% leads to the precipitation of the dissolved calcium as brushite and thus prevents a retentive etching pattern.

See also

literature

  • CU Shepard : Five new mineral species. In: American Journal of Science and Arts. Volume 22 (1856), pp. 96-99
  • Gideon Emmet Moore: On brushite, a new mineral occurring in phosphatic guano , in: The American Journal of Science and Arts , Volume 39 (1865), pp. 43–44 ( PDF 126.6 kB )
  • Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p. 626 .

Web links

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

Individual evidence

  1. Mineral Atlas: Brushite
  2. a b Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 5th completely revised and supplemented edition. Weise, Munich 2008, ISBN 978-3-921656-70-9 .
  3. a b c d 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.  490 .
  4. Webmineral - brushite
  5. a b Brushite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 64.8 kB )
  6. a b c Mindat - Brushite
  7. Mindat - Number of locations for brushite
  8. Find location list for brushite in the Mineralienatlas and Mindat
  9. Albrecht Hesse: Brushitsteine in dogs . In: Animal Stone Letter 7: 2/2013. (see also urinary stones from dogs , PDF 62.8 kB, modified from A. Hesse)