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Braccoite

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About BraccoiteHide

Roberto Bracco
Formula:
NaMn2+5[Si5As5+O17(OH)](OH)
Colour:
Brown-red
Lustre:
Vitreous, Resinous
Specific Gravity:
3.56 (Calculated)
Crystal System:
Triclinic
Name:
Named by F. Cámara, E. Bittarello, M.E. Ciriotti, F. Nestola, F. Radica, and M. Marchesini in 2015 in honour of Dr Roberto Bracco (b. 1959), a systematic minerals collector with a special interest in manganese minerals.
The As analogue of saneroite, which is topologically identical. Chemically somewhat similar to johninnesite.

The structure details: (1) five-repeat single isolated chains of SiO4 tetrahedra, with sixth tetrahedron as an appendix; (2) layer of tet‑
rahedra || (111) formed by lateral repeat of chains by a center of symmetry; (3) 5 octahedral sites (Mn) form a band || two single chains of tetrahedra (above and below); (4) channels, laterally separating the bands, partially occupied by two independent Na atoms.


Classification of BraccoiteHide

Approved
Approval Year:
2013
First Published:
2015

Physical Properties of BraccoiteHide

Vitreous, Resinous
Transparency:
Translucent
Colour:
Brown-red
Streak:
Pale yellow
Comment:
Could not be measured due to size and intergrowth with tiragalloite
Tenacity:
Brittle
Cleavage:
None Observed
Fracture:
Irregular/Uneven
Density:
3.56 g/cm3 (Calculated)
Comment:
Couldn't be measured for the same reason as hardness

Optical Data of BraccoiteHide

Type:
Biaxial (+)
RI values:
nα = 1.749(1) nβ = 1.750(1) nγ = 1.760(1)
2V:
Measured: 26° (2), Calculated: 35°
Max Birefringence:
δ = 0.011
Image shows birefringence interference colour range (at 30µm thickness)
and does not take into account mineral colouration.
Surface Relief:
High
Pleochroism:
Weak
Comments:
Brownish-yellow (X), dark yellow (Y), yellow (Z)

Chemical Properties of BraccoiteHide

Formula:
NaMn2+5[Si5As5+O17(OH)](OH)
IMA Formula:
NaMn2+5[Si5O14(OH)](AsO3)(OH)
Common Impurities:
Mn(III),Mg,V

Crystallography of BraccoiteHide

Crystal System:
Triclinic
Class (H-M):
1 - Pedial
Space Group:
P1
Cell Parameters:
a = 9.740(6) Å, b = 9.900(7) Å, c = 9.085(6) Å
α = 92.06(5)°, β = 117.41(5)°, γ = 105.27(5)°
Ratio:
a:b:c = 0.984 : 1 : 0.918
Unit Cell V:
740.37 ų
Z:
2
Comment:
Different space group from ima and abs of type description

X-Ray Powder DiffractionHide

Powder Diffraction Data:
d-spacingIntensity
3.042(57)
3.005(61)
2.973(82)
2.821(100)
2.696(87)
2.614(29)
1.673(30)
Comments:
From Type Description.

Type Occurrence of BraccoiteHide

General Appearance of Type Material:
subhedral crystals (a few hundred microns across) in brown-red coloured thin masses a few centrimeters in size
Place of Conservation of Type Material:
Type material is deposited in the mineralogical collections of the Museo Regionale di Scienze Naturali di Torino, Sezione di Mineralogia, Petrografia e Geologia, Torino, Italy, catalogue number M/15939
Associated Minerals at Type Locality:

Synonyms of BraccoiteHide

Fluorescence of BraccoiteHide

Other InformationHide

Notes:
Raman bands [cm-1]: ~829, 907, 932, 706w, 748w (SiO4 and AsO4 groups); overlapping bands centered at 3361 and 3507 (OH stretching)
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for BraccoiteHide

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Cámara, F., Bittarello, E., Ciriotti, M.E., Nestola, F., Radica, F., Marchesini, M. (2013) Braccoite, IMA 2013-093. CNMNC Newsletter No. 18. Mineralogical Magazine: 77: 3249-3258.
Cámara, F., Bittarello, E., Ciriotti, M. E., Nestola, F., Radica, F., Marchesini, M. (2015) As-bearing new mineral species from Valletta mine, Maira Valley, Piedmont, Italy: II. Braccoite, NaMn2+5[Si5AsO17(OH)](OH), description and crystal structure. Mineralogical Magazine: 79(1): 171-189.

Internet Links for BraccoiteHide

Localities for BraccoiteHide

ⓘ - Click for further information on this occurrence. ? - Indicates mineral may be doubtful at this locality. - Good crystals or important locality for species. - World class for species or very significant. (TL) - Type Locality for a valid mineral species. (FRL) - First Recorded Locality for everything else (eg varieties). Struck out - Mineral was erroneously reported from this locality. Faded * - Never found at this locality but inferred to have existed at some point in the past (eg from pseudomorphs.)

All localities listed without proper references should be considered as questionable.
Italy (TL)
 
  • Piedmont
    • Cuneo Province
      • Maira Valley
        • Canosio
          • Vallone della Valletta
Cámara, F., Bittarello, E., Ciriotti, M.E., Nestola, F., Radica, F. and Marchesini, M. (2013) Braccoite, IMA 2013-093. CNMNC Newsletter No. 18, December 2013, page 3256; Mineralogical Magazine, 77, 3249-3258 ; Cámara, F., Ciriotti, M.E., Bittarello, E., Nestola, F., Massimi, F., Radica, F., Costa, E., Benna, P., Piccoli, G.C. (2014) Arsenic-bearing new mineral species from Valletta mine, Maira Valley, Piedmont, Italy: I. Grandaite, Sr2Al(AsO4)2(OH), description and crystal structure. Mineralogical Magazine, 78, 757-774; Cámara, F., Bittarello, E., Ciriotti, M.E., Nestola, F., Radica, F., Marchesini, M. (2015) Arsenic-bearing new mineral species from Valletta mine, Maira Valley, Piedmont, Italy: II. Braccoite, NaMn2+5[Si5AsO17(OH)](OH), description and crystal structure. Mineralogical Magazine, 79, 171-189; Kampf, A.R., Cámara, F., Ciriotti, M.E., Nash, B.P., Balestra, C., Chiappino, L. (2016): Castellaroite, Mn2+3(AsO4)2⋅4.5H2O, a new mineral from Italy related to metaswitzerite. European Journal of Mineralogy, 28, 687-696; Cámara, F., Bittarello, E., Ciriotti, M.E., Nestola, F., Radica, F., Massimi, F., Balestra, C., Bracco, R. (2017a) As-bearing new mineral species from Valletta mine, Maira Valley, Piedmont, Italy: III. Canosioite, Ba2Fe3+(AsO4)2(OH), description and crystal structure. Mineralogical Magazine, 81, 305–317.
Mineral and/or Locality  
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