Calclacite

from Wikipedia, the free encyclopedia
Calclacite
General and classification
chemical formula Ca (CH 3 COO) Cl • 5H 2 O
Mineral class
(and possibly department) 		Organic compounds
System no. to Strunz
and to Dana 		10.AA.25 ( 8th edition : IX / A.02)
02.50.04.01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 1 / a (No. 14, position 3)Template: room group / 14.3
Lattice parameters a  = 11.51  Å ; b  = 13.72 Å; c  = 6.82 Å
β  = 116.7 °
Formula units Z  = 4
Physical Properties
Mohs hardness 1
Density (g / cm 3 ) measured: 1.5; calculated: 1.55
Cleavage Please complete!
colour White
Line color White
transparency translucent
shine Silky gloss
Crystal optics
Refractive indices n α  = 1.468
n β  = 1.484
n γ  = 1.515
Birefringence δ = 0.047
Optical character biaxial positive
Axis angle 2V = measured: 80 °; calculated: 74 °
Other properties
Chemical behavior easily soluble in water

Calclacite is an extremely rare mineral from the mineral class of " organic compounds " with the chemical composition Ca (CH 3 COO) Cl · 5H 2 O and is therefore chemically a calcium acetate containing chloride .

Calclacite crystallizes in the monoclinic crystal system and is formed exclusively by the influence of wood (e.g. in showcases or display cases) on acid-sensitive, calcium-containing minerals, fossils or archaeological artifacts. It can be found on these in the form of white crusts or fibrous aggregates.

Calclacite is therefore of anthropogenic origin and strictly speaking does not comply with the rules for the recognition of minerals that have been in force since the founding of the International Mineralogical Association (IMA).

With a Mohs hardness of 1, calclacite is one of the soft minerals that, like the reference mineral talc, can be scratched with the fingernail.

Etymology and history

Calclacite was first described in 1945 by René van Tassel, who named the mineral based on its two main components calcium and acetate .

Calclacite was described before the IMA was founded in 1958 and is generally recognized as a mineral. This recognition was adopted by the IMA as a so-called " grandfathered mineral", although the mineral is of anthropogenic origin and therefore no longer complies with the rules that have been in force since 1998, according to which a material must not be influenced, caused or manufactured by humans in order to be accepted as a mineral to become.

classification

In the outdated, but still in use 8th edition of the mineral classification according to Strunz , the calclacite belonged to the mineral class of "organic compounds" and there to the department of "salts of organic acids", where together with abelsonite , dashkovaite , earlandite , formicaite , hoganite , julienite , Kafehydrocyanit , Mellit , Paceit the group "Other organic salts, including mellates , citrates and acetates " with the system no. IX / A.02 formed.

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 calclacite to the category of "salts of organic acids". However, this is now clearly divided according to the substance groups that form the basis of the respective mineral, so that calclacite can be found according to its composition in the sub-section "Acetate", where it is the only member of the unnamed group 10.AA.25 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns calclacite to the class and department of the same name of "organic minerals". Here he is the only member of the unnamed group 50.02.04 within the sub-section “ Salts of organic acids (mellitates, citrates, cyanates and acetates) ”.

Crystal structure

Calclacite crystallizes monoclinically in the space group P 2 1 / a (space group no.14, position 3) with the lattice parameters a  = 11.51  Å , b  p = 13.72 Å, c  = 6.82 Å and β  = 116, 7 ° and 4 formula units per unit cell . Template: room group / 14.3

properties

Calclacite is easily soluble in water and therefore not resistant. The hygroscopic crystals in the air at high humidity to dissolve .

From a chemical point of view, calclacite is a calcium salt of acetic acid with the chemical formula Ca (CH 3 COO) Cl · 5H 2 O. It is of purely anthropogenic origin and would therefore no longer meet the requirements of the IMA for a mineral today .

Education and Locations

Calclacite is not a naturally occurring mineral. It forms on calcium-containing minerals , which z. B. be stored in museums in wooden boxes or wooden showcases. Wood in general and old oak in particular has the property of slowly releasing acetic acid . This can then react over a long period of time with acid-sensitive, calcium-containing minerals and form calclacite. An overview of the reactions that lead to the formation of acetic acid can be found under thermally modified wood .

In addition to the formation on calcium-containing minerals, calclacite was also found on fossils and archaeological finds such as ceramic shards.

See also

literature

  • René van Tassel: Une efflorescense d'acetatochlorure de cacium sur des roches calcaires dans des collections . In: Bulletin du Musée Royal d'Histoire Naturelle de Belgique . tape 21 , no. 26 , 1945, p. 1–11 ( rruff.info [PDF; 410 kB ]).
  • Calclacite . 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; 65 kB ; accessed on September 9, 2017]).

Web links

Individual evidence

  1. ↑ a b c d e R. van Tassel: On the crystallography of calclacite, Ca (CH3COO) Cl.5H2O , in: Acta Crystallographica , Volume 11, Chapter 10 (October 1958), doi : 10.1107 / S0365110X58002000
  2. ↑ Calclacite . 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; 65  kB ; accessed on September 9, 2017]).
  3. ↑ a b c d e Mindat - Calclacite
  4. ^ Ernest H. Nickel, Joel D. Grice: The IMA Commission on new Minerals and Mineral Names: Procedures and Guidelines on Mineral Nomenclature, 1998 . In: The Canadian Mineralogist . tape 36 , 1998, pp. 2 ( edu.au [PDF; 328 kB ; accessed on September 9, 2017]).
  5. ↑ B. Jung, E. Roffael: About the acidity of native wood species . In: European Journal of Wood and Wood Products . tape 60 , no. 2 , 2002, p. 154 , doi : 10.1007 / s00107-001-0278-5 .