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Unnamed (Ca Hydroxide Arsenate Hydrate)

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Formula:
Ca2(OH)(AsO4) · 2H2O
Formula given in the various literature also as 4CaO·As2O5·5H2O, Ca3(AsO4)2·Ca(OH)2·4H2O or Ca4(OH)2(AsO4)2·4H2O.
Colour:
Colourless, white, pale blue
Lustre:
Vitreous
Crystal System:
Monoclinic
Anthropogenic phase detected on samples from the Clara mine, Black Forest, Germany. The occurrence is due to the use of concrete underground. Using these samples, the previously unknown crystal structure was determined (Kolitsch, 2024).

The synthetic compound known from studies of the system Ca-As-O-H and reported to be stable in the pH range 11-12 (Bothe & Brown 1999, 2002).


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Unique IdentifiersHide

Mindat ID:
496544
Long-form identifier:
mindat:1:1:496544:8

Physical Properties of Unnamed (Ca Hydroxide Arsenate Hydrate)Hide

Lustre:
Vitreous
Transparency:
Transparent, Translucent
Colour:
Colourless, white, pale blue

Chemistry of Unnamed (Ca Hydroxide Arsenate Hydrate)Hide

Mindat Formula:
Ca2(OH)(AsO4) · 2H2O

Formula given in the various literature also as 4CaO·As2O5·5H2O, Ca3(AsO4)2·Ca(OH)2·4H2O or Ca4(OH)2(AsO4)2·4H2O.
Element Weights:
Element% weight
O41.158 %
Ca29.457 %
As27.533 %
H1.852 %

Calculated from ideal end-member formula.
Elements listed:
As, Ca, H, O - search for minerals with similar chemistry
Common Impurities:
Si

Crystallography of Unnamed (Ca Hydroxide Arsenate Hydrate)Hide

Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
P21/b
Setting:
P1 21/c 1
Cell Parameters:
a = 6.178(1) Å, b = 15.688(3) Å, c = 6.876(1) Å
β = 99.67(3)°
Ratio:
a:b:c = 0.394 : 1 : 0.438
Unit Cell V:
656.96 ÅÂģ
Morphology:
Lath-shaped or blocky.
Comment:
Data from anthropogenic crystals (Kolitsch, 2024).

X-Ray Powder DiffractionHide

Powder Diffraction Data:
d-spacingIntensity
7.82 Å(100)
6.08 Å(30)
4.18 Å(60)
4.04 Å(60)
3.18 Å(80)
2.97 Å(40)
2.83 Å(80)
2.71 Å(30)
2.50 Å(60)
Reference:
Pierrot, Roland (1964) Contribution à la minÃĐralogie des arsÃĐniates calciques et calcomagnÃĐsiens naturels. Bulletin de MinÃĐralogie, 87 (2) 169-211 doi:10.3406/bulmi.1964.5727(with unindexed powder pattern, later incorporated into the ICDD database as ICDD-PDF 18-289)
Comments:
Unindexed.

Synonyms of Unnamed (Ca Hydroxide Arsenate Hydrate)Hide

Other InformationHide

Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

Internet Links for Unnamed (Ca Hydroxide Arsenate Hydrate)Hide

References for Unnamed (Ca Hydroxide Arsenate Hydrate)Hide

Reference List:
Kolitsch, U. (2024): Crystal structure of anthropogenic Ca2(OH)(AsO4)·2H2O found in the Clara mine, Black Forest, Germany. Mitteilungen der Österreichischen Mineralogischen Gesellschaft 170, 121 (abstract). https://www.uibk.ac.at/media/filer_public/ca/1f/ca1fa958-2548-4cb6-a285-54de4325c605/3_minwien_abstracts.pdf
Zhu, Y., Zhang, X., Xie, Q., Wang, D., Cheng, G. (2006): Solubility and stability of calcium arsenates at 25°C. Water, Air, and Soil Pollution, 169, 221-238.
GuÃĐrin, H. (1941): Sur les arsÃĐniates alcalino-terreux. Étude du systÃĻme As2O5-OCa-H2O. Annales de Chimie 16, 101-153.
Pierrot, Roland (1964) Contribution à la minÃĐralogie des arsÃĐniates calciques et calcomagnÃĐsiens naturels. Bulletin de MinÃĐralogie, 87 (2) 169-211 doi:10.3406/bulmi.1964.5727(with unindexed powder pattern, later incorporated into the ICDD database as ICDD-PDF 18-289)
Blaß, GÞnter; Graf, Hans-Werner (1995) Namibit, ein Neufund aus dem Schwarzwald [Namibite, a new discovery from the Black Forest]. Mineralien-Welt, 6 (6). 20-22(also includes descriptions of several Ca arsenates from the Clara mine)
Bothe, James V, Brown, Paul W (1999) The stabilities of calcium arsenates at 23¹1°C. Journal of Hazardous Materials, 69. 197-207 doi:10.1016/s0304-3894(99)00105-3
Bothe, James V., Brown, Paul W. (1999) Arsenic Immobilization by Calcium Arsenate Formation. Environmental Science & Technology, 33 (21). 3806-3811 doi:10.1021/es980998m
Bothe, James V., Brown, Paul W. (2004) CaO-As2O5-H2O System at 23°¹ 1°C. Journal of the American Ceramic Society, 85 (1). 221-224 doi:10.1111/j.1151-2916.2002.tb00069.x
MOON, D, DERMATAS, D, MENOUNOU, N (2004) Arsenic immobilization by calcium–arsenic precipitates in lime treated soils. Science of The Total Environment, 330 (1). 171-185 doi:10.1016/j.scitotenv.2004.03.016

Localities for Unnamed (Ca Hydroxide Arsenate Hydrate)Hide

This map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.

Locality ListHide

- This locality has map coordinates listed. - This locality has estimated coordinates. ⓘ - Click for references and further information on this occurrence. ? - Indicates mineral may be doubtful at this locality. - Good crystals or important locality for species. - World class for species or very significant. (TL) - Type Locality for a valid mineral species. (FRL) - First Recorded Locality for everything else (eg varieties). Struck out - Mineral was erroneously reported from this locality. Faded * - Never found at this locality but inferred to have existed at some point in the past (e.g. from pseudomorphs).

All localities listed without proper references should be considered as questionable.
Germany
 
  • Baden-WÞrttemberg
    • Freiburg Region
      • Ortenaukreis
        • Oberwolfach
Kolitsch (2024) +1 other reference
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