Childrenite
| Childrenite | |
|---|---|
 |
|
| General and classification | |
| chemical formula |
|
|
Mineral class (and possibly department) |
Phosphates, arsenates and vanadates |
|
System no. to Strunz and to Dana |
8.DD.20 ( 8th edition : VII / D.14) 07.22.01.01 |
| Crystallographic Data | |
| Crystal system | orthorhombic |
| Crystal class ; symbol | orthorhombic-pyramidal; mm 2 |
| Space group | Bbe 2 (No. 41, position 2) or Bbem (No. 64, position 5) |
| Lattice parameters | a = 10.395 Å ; b = 13.394 Å; c = 6.918 Å |
| Formula units | Z = 8 |
| Physical Properties | |
| Mohs hardness | 5 |
| Density (g / cm 3 ) | measured: 3.11 to 3.19; calculated: 3.12 to 3.15 |
| Cleavage | indistinct after {100} |
| Break ; Tenacity | slightly scalloped to uneven |
| colour | yellow-brown to brown |
| Line color | White |
| transparency | transparent to translucent |
| shine | Glass gloss, resin gloss |
| Crystal optics | |
| Refractive indices |
n α = 1.644 to 1.649 n β = 1.662 to 16.830 n γ = 1.671 to 1.691 |
| Birefringence | δ = 0.027 to 0.042 |
| Optical character | biaxial negative |
| Axis angle | 2V = measured: 40 to 45 °; calculated: 50 ° |
| Pleochroism | visible: X = yellow; Y = pink; Z = light pink to colorless |
Childrenite is a rather seldom occurring mineral from the mineral class of “ phosphates , arsenates and vanadates ” with the idealized chemical composition Fe 2+ Al [(OH) 2 | PO 4 ] · H 2 O and is therefore chemically a water-containing iron - aluminum -Phosphate with additional hydroxide ions .
Since childrenite and eosphorite (Mn 2+ Al [(OH) 2 | PO 4 ] · H 2 O) form a complete mixed series , part of the iron in natural childrenite samples is often replaced ( substituted ) by manganese . In various sources, the chemical formula is therefore also given as (Fe 2+ , Mn 2+ ) Al [(OH) 2 | PO 4 ] · H 2 O.
Childrenite crystallizes in the orthorhombic crystal system and develops pyramidal crystals with a thick-tabular to short-prismatic habit , but is also found in the form of radial or massive mineral aggregates and crusty coatings with a resin-like to glass-like gloss on the surfaces. The transparent to translucent crystals are yellow-brown to brown in color. However, Childrenit leaves a white line on the notice board .
Etymology and history
Childrenite was first discovered in 1823 near Tavistock (Devon) in England and described by Henry James Brooke (1771-1857), who named the mineral after the English chemist and mineralogist John George Children (1777-1852).
classification
Already in the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the Childrenite belonged to the mineral class of "Phosphates, Arsenate and Vanadates" and there to the department of "Water-containing phosphates with foreign anions ", where it was named after the "Childrenit- Row "with the system no. VII / D.14 and the other members Eosphorit and Ernstit .
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 childrenite to the section of “phosphates etc. with additional anions; with H 2 O “. However, this is further subdivided according to the relative size of the cations involved and the ratio between the other anions (OH etc.) and the phosphate, arsenate or vanadate complex (RO 4 ), so that the mineral can be classified in the sub-section " With only medium-sized cations; (OH etc.): RO 4 = 2: 1 "can be found, where the" childrenite group "with the system no. 8.DD.20 and the other members Eosphorit and Ernstit.
The systematics of minerals according to Dana also assigns childrenite to the class of "phosphates, arsenates and vanadates" and there to the category of "water-containing phosphates etc., with hydroxyl or halogen". Here he is also the namesake of the "Childrenit group" with the system no. 42.07.01 and the other members Eosphorit, Ernstit and Sinkankasit within the subdivision of " Water-containing phosphates etc., with hydroxyl or halogen and the general composition (AB) 5 (XO 4 ) 3 Z q • x (H 2 O) " Find.
Crystal structure
Childrenite crystallizes orthorhombically in space group Bbe 2 (space group no. 41, position 2) or Bbem (no. 64, position 5) with the lattice parameters a = 10.395 Å ; b = 13.394 Å and c = 6.918 Å as well as 8 formula units per unit cell .
Education and Locations
Childrenite is formed as a conversion product from primary phosphate minerals under the influence of hydrothermal solutions at low temperatures in complex granite - pegmatites . Accompanying minerals include apatite , kaolinite , pyrite , quartz , siderite , various tourmalines and zinnwaldite .
As a rather rare mineral formation, Childrenite can sometimes be abundantly available at various locations, but overall it is not very widespread. So far, around 100 sites (as of 2018) have been documented for Childrenit worldwide. In England , the mineral could be discovered in addition to its type locality Tavistock, more precisely on the Tavistock Canal , in many places in the Tavistock district or in the county of Devon , such as Bere Ferrers, Buckland Monachorum, Horrabridge, Mary Tavy and Tavistock Hamlets. Other sites are known in the counties of Cornwall and Cumbria .
In Germany, the mineral has so far only been found on the Hühnerkobel near Rabenstein in the area of Waidhaus (Hagendorf, Silbergrube) in Bavaria and in the Sauberg mine and on the Greifensteinen near Ehrenfriedersdorf in Saxony.
In Austria, the mineral occurred only in the Spittal an der Drau district , more precisely on the Hahnenkofel and at Laggerhof near Lake Millstatt and on Wolfsberg .
Other locations are in Afghanistan, Argentina, Australia, Bolivia, Brazil, Finland, France, Japan, Canada, Kosovo, Namibia, Portugal, Rwanda, Sweden, Spain and in the United States of America (USA).
See also
literature
- HJA Brooke: On some undescribed minerals. Childrenite . In: The Quarterly Journal of Science, Literature, and the Arts . tape 16 , 1823, pp. 274–277 ( rruff.info [PDF; 848 kB ; accessed on May 25, 2018]).
- G. Giuseppetti, C. Tadini: The crystal structure of childrenite from Tavistock (SW England), Ch 89 Eo 11 term of childrenite-eosphorite . In: New yearbook for mineralogy, monthly books . 1984, p. 263-271 .
- Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 649 (first edition: 1891).
Web links
- Mineral Atlas: Childrenit (Wiki)
- RRUFF Database-of-Raman-spectroscopy - Childrenite (English)
- American-Mineralogist-Crystal-Structure-Database - Childrenite (English)
Individual evidence
- ↑ a b IMA / CNMNC List of Mineral Names; March 2018 ( Memento from June 11, 2018 in the Internet Archive ) (PDF 1.65 MB)
- ^ A b Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 504 .
- ↑ a b Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th completely revised and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
- ↑ Webmineral - Childrenite (English)
- ↑ a b The former name of this room group was Bba 2.
- ↑ a b The former name of this space group was Bbam .
- ↑ a b c American-Mineralogist-Crystal-Structure-Database - Childrenite (English)
- ^ Childrenite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 66 kB ]).
- ↑ a b c d e Mindat - Childrenite (English)
- ↑ Mindat - Number of locations for Childrenite
- ^ Mineralienatlas: type locality Tavistock Canal
- ↑ Find location list for Childrenite at the Mineralienatlas and at Mindat