Caoxite

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Caoxite
General and classification
other names

IMA 1996-012

chemical formula Ca (C 2 O 4 ) • 3H 2 O
Mineral class
(and possibly department) 		Organic compounds / oxalates
System no. to Strunz
and to Dana 		10.AB.50 ( 8th edition : IX / A.01)
50.01.02.02
Similar minerals Weddellite , whewellite
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Room group (no.) P 1 (No. 2)
Lattice parameters a  = 6.10  Å ; b  = 7.14 Å; c  = 8.43 Å,
α  = 76.5 °; β  = 70.3 °; γ  = 70.7 °
Formula units Z  = 2
Physical Properties
Mohs hardness 2 to 2.5
Density (g / cm 3 ) calculated: 1.85
Cleavage good after {010}
Break ; Tenacity uneven
colour White
Line color White
transparency transparent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.483
n β  = 1.516
n γ  = 1.533
Birefringence δ = 0.0500
Optical character biaxial negative

Caoxit is an extremely rare mineral from the mineral class of " organic compounds ". It crystallizes in the triclinic crystal system with the chemical composition Ca (C 2 O 4 ) · 3H 2 O, so it is chemically a calcium oxalate .

Caoxit usually develops colorless and transparent, polycrystalline spherulites up to about 0.5 mm in size. Small, elongated, tabular crystals of similar size are also known. The line color of the mineral is white and, with a Mohs hardness of 2 to 2.5, it is one of the more soft minerals.

Etymology and history

The name is an acronym with two meanings:

  • C entennial A nniversary o f X -rays:
The acronym refers to the " centenary [the discovery] of X-rays [by Wilhelm Conrad Roentgen ] " in 1995. This acronym is a tribute to Wilhelm Conrad Röntgen, who discovered the rays named after him in 1895 ( English X -rays ). X-rays are an important aid to structure elucidation in mineralogy . The structure of Caoxit was u. a. uncovered using these techniques in the anniversary year 1995.
  • Ca lcium ox alate .

Caoxit was first discovered in the Cerchiara mine (Cerchiara Mine) near Borghetto di Vara in the Italian region of Liguria. Just one year after its description by R. Basso, G. Lucchetti, L. Zefiro and A. Palenzona, Caoxite was recognized as a mineral by the IMA in 1996 (IMA 1996-012).

classification

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , Caoxit belonged to the mineral class of "organic compounds" and there to the department of "salts of organic acids", where together with Coskrenit- (Ce) , Glushinskit , Humboldtin , Levinsonite (Y) , lindbergite , minguzzite , moolooite , natroxalate , novgorodovaite , oxammite , stepanovite , Weddellite , wheatleyite , whewellite , zhemchuzhnikovite and Zugshunstit- (Ce) the independent "group of oxalates " with the system no. IX / A.01 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 Caoxit to the class of “organic compounds” and there to the section “salts of organic acids”. However, this section is further subdivided according to the type of salt-forming acid , so that the mineral can be found according to its composition in the sub-section "Oxalates", where it is the only member of the unnamed group 10.AB.50 .

The systematics of minerals according to Dana also assigns Caoxit to the class of "organic minerals" and there in the department of the same name. Here he can be found with Weddellite in the unnamed group 50.01.02 within the subdivision " Salts of organic acids (oxalates) ".

Education and Locations

Even if Caoxit is the salt of an organic acid, no biological processes have to be involved in its formation. Like whewellite, caoxite forms as an extremely rare primary mineral in hydrothermal deposits. Here in particular in crevices and passages of manganese and barium-rich, metamorphic ophiolites , whereby it can usually be found in small, millimeter-thick cracks. Accompanying minerals include quartz , barite and manganese oxides.

The only previously known site is:

The relevant type material is kept by the University of Genoa .

In addition to whewellite and weddellite, caoxite is a component of kidney stones.

Crystal structure

Caoxite crystallizes triclinically in the space group P 1 (space group no. 2) with the lattice parameters a  = 6.10  Å ; b  = 7.14 Å; c  = 8.43 Å; α = 76.5 °; β = 70.3 ° and γ = 70.7 ° as well as two formula units per unit cell .

Caoxite differs from Weddellite and Whewellite on the one hand in its crystal structure and on the other hand in the content of crystal water. In contrast to other mineral series containing crystalline water, there is no evidence here that caoxite is gradually transformed into whewellite via Weddellite.

See also

Individual evidence

  1. ↑ a b c d e 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. 720 .
  2. ^ Encyclopedia of Mineral Names: First Upsate (accessed October 18, 2011).
  3. ↑ Basso, R., G. Lucchetti, L. Zefiro, and A. Palenzona (1997) Caoxite, Ca (H2O) 3 (C2O4), a new mineral from the Cerchiara mine, northern Apennines, Italy.
  4. ^ New Mineral Names, American Mineralogist, 83 (1998) pp. 185-189 (English, accessed October 18, 2011).
  5. ↑ Catalog of Type Mineral Specimens (accessed October 18, 2011).
  6. ↑ La cristallurie le point de vue du biologiste (French, accessed October 18, 2011).
  7. ↑ Trpkovska, M., B. Šoptrajanov, and L. Pejov (2002), Reinvestigation of the infrared spectra of calcium oxalate monohydrate and its partially deuterated analogues, Bull. Chem. Technol. Macedonia, 21 (2), 111-116. online (accessed October 18, 2011).

literature

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