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Short Communications
MINERALOGICAL MAGAZINE, OCTOBER 1996,
VOL. 60, PP 841-842
Ferrazite is identical to gorceixite
D. Atencio Departamento de Mineralogia
e Petrologia
Instituto de Geociências, Universidade de São
Paulo
Caixa Postal 11348 - 05422, São Paulo, SP, Brasil
A. M. Clark Mineralogy Departament,
The natural History Museum,
Cromwell Road, London SW7 5BD, OK
The petrographer Dr. Jorge Belmiro de Araujo Ferraz
submitted for chemical analysis some pebbles ('fava')
from the late Eugen Hussa's collection, bearing Hussa's
own label'Pb-Al hydrophost. D.3.095. Neu'. The pebbles,
found in diamond washing, were discoid in shape, dark
yellowish wite, resembling old ivory, and in micro-sections
showed a granular structure. The results of the analysis
were published by Lee Moraes (-Rego) (1919 and 1920).
The provenance of the samples was not quoted by these
authors but was quoted by Ferraz (1928) and Palache
et al. (1951) as Diamantina, Minas Gerais, Brazil.
From the results of a preliminary analysis
it appeared to Lee and Moraes that, in addition to Pb,
Ba was also present, which led them to carry out a complete
analysis, leading to the following results: Ba0 8.87,
Ca0 traces, Pb0 45.63, Al2 03 3.48, Si02 2.44, P2 05
26.24, H2 0 14.20, total 100.86 wt%.
After deducting silica and alumina, possibly
derived from Kaolin and wavellite, the formula was quoted
as 3(Ba,Pb) 0-2P205- 8H20. The density of the pebbles
varied between 3.0 and 3.3. The mineral was named ferrazite
after Dr. J.B. A. Ferraz.
We have obtained a sample, with same
characteristics as above, from Dr. J. B. A. Ferraz'..
collection (now in the Museu de Geociências do
Instituto de Geociências da Universidade de São
Paulo) labelled as 'Ferrazita. Diamantina, Minas Gerais'
(Sample 41.5.8.1/3 - 625 A/1). The sample was identified
by X-ray powder diffraction (Table 1) and electron microprobe
chemical data (Table 2) as gorceixite, BaAl3 (PO4) (PO3OH)
(OH)6.
The density measured by Hussak and by
Lee and Moraes agrees with that for gorceixite (Dmeas
3.1 and Dcalc 3.41). A mean index of refraction now
measured is between 1.620 and 1.625, as in gorceixite.
We have also carried out an electron
probe and X-ray diffraction investigation of the type
specimen of ferrazite stored in The Natural History
Museum, London (B.M. 1920,131). The probe was carried
out on an energy-dispersive Hitachi instrument. The
pebble was examined in an unpolished state, so the results
should be regarded as semi quantitative. They are PbO
1.36, BaO 17.17, P205 19.09, FeO 0.52, ZnO 0.76, Al2O3
19.18 wt.%. The Debye-Scherrer X-ray film was taken
at the same spot on the sample (film nº X10211)
and is a good math for gorceixite.
Lee and Moraes did not quote the method
of chemical analysis but they probably analysed Pb and
Table 1. X-ray powder diffraction data
for 'ferrazite'and gorceixite
| d |
% |
d |
% |
hkl in Cm
|
| 5.775 |
99 |
5.7692 |
93 |
-1 1 0 |
-2 0 1+ |
| 3.527 |
68 |
3.592 |
56 |
-3 1 1 |
0 2 0+ |
| 3.003 |
100 |
3.0097 |
100 |
-3 1 2 |
0 2 1+ |
| 2.875 |
22 |
2.8852 |
15 |
0 0 2 |
2 2 0+ |
| 2.490 |
13 |
2.4952 |
11 |
-2 2 2 |
4 0 0 |
| 2.286 |
38 |
2.2925 |
39 |
1 1 2 |
-2 0 3+ |
| 2.227 |
19 |
2.2320 |
23 |
-1 3 1 |
-4 2 2 + |
| 2.030 |
10 |
2.0376 |
11 |
-1 1 3 |
4 2 0+ |
| 1.915 |
24 |
1.9197 |
29 |
-3 3 2 |
-6 0 1+ |
| 1.761 |
18 |
1.7626 |
20 |
-6 2 2 |
0 4 0+ |
| 1.683 |
9 |
1.6877 |
10 |
-5 1 4 |
1 3 2+ |
| |
|
1.6647 |
4 |
1 1 3 |
3 3 1+ |
| |
|
1.5780 |
1 |
-2 4 2 |
-5 3 3+ |
| |
|
1.5223 |
5 |
5 3 0 |
-7 1 4+ |
| 1.500 |
10 |
1.5058 |
18 |
-2 2 4 |
4 0 2 |
| |
|
1.4402 |
3 |
4 4 0 |
-8 0 4+ |
| 1.392 |
7 |
1.3977 |
9 |
-2 4 3 |
-5 3 4+ |
1.'Ferrazite' from Diamantina, Minas
Gerais, Brazil.
Cu-Kx radiation.
2. Gorceixite from the Big Fish River, Rapid Creek area,
Yokon Territury, Canada (Blanchard,1989).
Table 2. Electron microprobe chemical data fot 'ferrazite'and
gorceixite.
| |
1 |
2 |
Range |
Probe
standart |
| BaO |
30.00 |
23.52 |
(22.46-24.99) |
BaF2 |
| PbO |
|
0.53 |
(0.00-1.65) |
galena |
| SrO |
|
1.81 |
(1.29-2.25) |
celestine |
| CaO |
|
0.76 |
(0.66-0.84) |
wollastonite |
| Na2O |
|
0.06 |
(0.00-0.19) |
andesite |
| K2O |
|
0.10 |
(0.06-0.12) |
microcline |
| Al2O3 |
29.91 |
31.25 |
(29.54-32.42) |
corundum |
| Fe2O3 |
|
3.76 |
(1.11-8.40) |
hematite |
| P2O5 |
27.76 |
26.19 |
(25.13-27.28) |
InP |
| SiO2 |
|
0.95 |
(0.65-1.18) |
Wollastonite |
| H2O |
12.33 |
(11.07) |
|
|
| Total |
100.00 |
100.00 |
|
|
1. Gorceixite,ideal composition BaAl3
(PO4)(PO3OH)(OH)6.
2. 'Ferrazite' from Diamantina, Minas Gerais, Brazil
(Average of 10 analyses: H2O by difference).
Ba by gravimetry with precipitation of PbS04 and BaS04
, thus confusing Ba with Pb.
In inclusion, ferrazite is identical
to gorceixite. The name gorceixite (Hussak, 1906) was
published before ferrazite and therefore has historical
priority.
KEYWORDS: ferrazite, gorceixite, Minas Gerais, Brazil.
This nomenclature proposal ( number
95-F) was approved by CNMMN-IMA.
References
Blanchard. F.N.(1989) New X-ray powder
data for gorceixite, BaAl3 (PO4 )2 (0H)5 .H2O, an evaluation
of
d-spacings and intensities , pseudosymmetry and its
influence on the figure of merit. Powder Diffraction,
4. 227-30.
Ferraz, L.C.(1928) Compendio dos Minerales do Brasil
em forma de diccionário. P. 145.
Hussak, E. (1906) Über die sogenannten "Phosphat-Favas"
der diamantführenden Sande Brasiliens.
Tscherm. Mineral.Petrog. Mitt., 25, 335-44.
Lee, T. H. Ad Moraes, L. F. (1919) On ferrazite? a new
associet of diamond. Amer.J. Sci., ser 4, 48. 353.
Lee, T. H. and Moraes-Rego, L. F. (1920) Ferrazita,
um novo satellite do diamante. Annaes da Escola de Minas,
16, 59-60.
Palache, C., Berman, H. Ad Frondel, C. (1951) The System
of Mineralogy of J.M.Dana & E.S. Dana. 7th. Edition,
v. II, 832-3.
[Manuscript received 14 March 1996: accept
16 April 1996]
Copyright the Mineralogical Society
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