Home > Mineral Abstracts > CanMin Vol. 35, pp. 1541-1549 (1997)




Vol. 35, pp. 1541-1549 (1997)



Quintinite-2H, Quintinite-3T, Charmarite-2H, Charmarite-3T and Caresite-3T,
a new group of carbonate minerals related
to the hydrotalcite-manasseite group


George Y. Chao*
Ottawa-Carleton Geoscience Centre, Department of Earth Sciences,
Carleton University, Ottawa, Ontario K1S 5B6



Robert A. Gault1
Research Division, Canadian Museum of Nature,
Ottawa, Ontario K1P 6P4


ABSTRACT

     Charmarite-2H, charmarite-3T, quintinite-2H, quintinite-3T and caresite-3T are a group of new carbonate minerals with the general formula M2+4Al3+2(OH)12CO3 3H2O (4:2 minerals). They are structurally and chemically related to the hydrotalcite- manasseite group (6:2 minerals).  Superlattice reflections in the single-crystal X-ray photographs suggest ordering of cations in the 4:2 minerals, whereas the cations of the 6:2 minerals are disordered.  2H and 3T designate the 2-layered hexagonal and 3-layered trigonal structures, respectively.  All five species are late-stage hydrothermal minerals in alkaline rocks, and are associated with many rare mineral species.  Quintinite-2H occurs at Jacupiranga mine, São Paulo, Brazil; charmarite-2H, charmarite-3T, and quintinite-3H occur at Mont Saint-Hilaire, Quebec; caresite-3T occurs at Mont Saint-Hilaire and at the Corporation Quarry, Montreal, Quebec.

     In habit, they range from thin plates to thick tabular crystals, in some cases forming pyramidal or rosette-like aggregates.  They generally range from yellow to brown, occasionally colorless to pale blue.  All are transparent, with a white streak and vitreous luster, are non-fluorescent, and have a Mohs hardness of approximately 2.  All are brittle, with a perfect {001} cleavage and uneven fracture.  The measured densities are:  charmarite-2H 2.47(1), charmarite-3T 2.48(1), quintinite-2H and quintinite-3T 2.14(1), caresite-3T 2.59(1) g/cm3.  Charmarite-2H is uniaxial negative, w 1.587(1) and e 1.547(1); charmarite-3T is uniaxial negative, w 1.587(1) and e undetermined; quintinite-2H is uniaxial negative, w 1.533(1) and
e 1.533(1); quintinite-3T is uniaxial positive or negative, w 1.533(1) and
e 1.533(1); caresite-3T is uniaxial negative, w 1.599(1) and e 1.570(1).
All are generally pleochroic, with only the near-end-member quintinite-3T being non-pleochroic.

Charmarite-2H is hexagonal, space group P6322,
a 10.985(5), c 15.10(2) Å, V 2366(4) Å3, Z = 4;

Charmarite-3T is trigonal, P3112 or P3212
a 10.985(3), c 22.63(3) Å, V 2366(4) Å3, Z = 6;

Quintinite-2H is hexagonal, P6322
a 10.571(1), c 15.139(7) Å, V 1465(1) Å3, Z = 4;

Quintinite-3T is trigonal P3112 or P3212
a 10.558(2), c 22.71(3) Å, V 2192(3) Å3, Z = 6;

Caresite-3T is trigonal P3112 or P3212
a 10.805, c 22.48(3) Å, V 2273(4) Å3, Z = 6

     The following ideal formulae were developed from electron-microprobe analysis coupled with TGA-EGA data in some cases:


Charmarite-2H and charmarite-3T:

Mn4Al2(OH)12CO3 · 3H2O;

Quintinite-2H and quintinite-3T:

Mg4Al2(OH)12CO3 · 3H2O;

Caresite-3T: Fe4Al2(OH)12CO3 · 3H2O

     IR spectra are given for all five species.

Keywords:  charmarite-2H, charmarite-3T, quintinite-2H, quintinite-3T and caresite-3T, new mineral species, hydrotalcite, manasseite, Jacupiranga mine, Brazil, Mont Saint-Hilaire, Corporation Quarry, Montreal, Quebec.

* Present address:  2031 Delmar Drive Ottawa, Ontario K1H 5P6
1 E-mail address:  rgault@mus-nature.ca



© 1997  The Canadian Mineralogist