CAFARSITE

Ca₈(Ti,Fe,Mn)_6-7(AsO₃)₁₂.4H₂O

Cafarsite was first described as a new mineral in 1966 by Graeser ¹. Although this mineral was found before it was never recognised as a new mineral. In the first description of cafarsite the mineral was described as an iron arsenate ¹. The name was derived from its chemical composition calcium-iron-arsene Ca-F(e)-Ars-ite.

A detailed study of the crystal structure of cafarsite by Edenharter et al. showed that cafarsite was not an arsenate but actually an arsenite ². The cubic unit cell with a lattice constant a = 15.984 ± 0.004 Å contains four of the above named structural formula units. The cafarsite crystal structure belongs to the space group P_n3 (T_h²). In the structure the arsene atoms are positioned in a trigonal pyramidal coordination by three oxygen atoms. The pyramids are not connected to each other. Calcium atoms are found in two different positions as is the iron. The socalled Ca(1) and Fe(2) octahedra share edges. The Ca(2) atoms are irregularly coordinated by eight oxygen atoms and the polyhedra share edges or corners with the octahedra. The Fe(1) atoms are in a distorted four coordination of oxygen atoms, which is very rare for iron ².

1.            S. Graeser, Schweiz. Mineral. Petrogr. Mitt., 46, 367 (1966).

2.            A. Edenharter, W. Nowacki and M. Weibel, Schweiz. Mineral. Petrogr. Mitt., 57, 1 (1977).

SELECTED REFERENCES ON SPECTROSCOPY OF CAFARSITE:

1       J.T. Kloprogge and R.L. Frost (1999) Raman spectroscopy study of cafarsite. Applied Spectroscopy, 53(7), 874-879.

2.      M. Boscardin and V. Mattioli (1981) Lapis, 6, 30-.

3.            J.A. Gadsden, Infrared Spectra of Minerals and Related Inorganic Compounds. Butterworths & Co. Ltd., London, U.K., 277 pp (1975).

Original spectra shown for this mineral can be obtained on request from J.T. Kloprogge (E-mail t.kloprogge@qut.edu.au), or R.L. Frost (E-mail r.frost@qut.edu.au).

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