Canadian Mineralogist
Vol. 16, pp.69-73 (1978)

MINERALFROM BROSSO,ITALYA NEW CARBOBORATECANAVESITE,
FRANCHINI-ANGELA,GIOVANNI FERRARIS, MARINELLA'G. Spqid' deltUniversitd'
Istituto di Mineralogia, Cristallografia e Geochimica
ItalyTorino,
10123
24
Via San MaSsino,
Er.lp PAOLO ORLANDI
Istituto di Mineralogiae PetrogryfiadelfUniversitd,Via S. Maria, 53-56100 Pisa' Italy

ABSTRACT
Canavesite occurs as milky-white rosette-like agetregFtesof fibers on ludwigite and magnetite skarns
in the abandoned iron mine of Brosso @iedmont'Ilaly). It is monoclinic (diffraction symbol 2/mP-/-)
with 423.49(2), b 6.164{6), c 21.91Q)4,, F 114.9t(9)';D*t 1.790 g om{ for Z = 12. The strongest reflections in the X-ray powder pattern are: 9.54(100)(202\, s.t2(40)(201), 7.80(18X102,301),4.56(21)(5-01,503) and 3.1104 $r@07).
The fibers areelongate [010] and show one or morc {h0l} cleavages; optically tley are biaxial, 2V very latge, Z=b, na t.4s5(4), np I.494(4), nt l.5O5Q). DTA, TGA
and higb-temperature X-ray powder analyses document several breakdown reactions, finally leaving
an assemblageof Msg(BOs)zand MgO above 800"C.
TGA, in particular, gives cumulative weight lossesof 10, 20, 30, 39,43, 50 and 56% at 95, 190, 300,410,475,625 and 875"C, respectively. The infraredabsorption spectrum shows OH', COgL and BOs&;
the chemical analysis gives tle formula Mg:.os(COs)l.oeGIBOs)o.sa.
4.9 1H:O.

indique la pr6sencede OH-, COr& et BO3&'D-aprbs
I'analysechimique,la formule s'6crit Mgr.ot(COt)4.9lH,zO,) o.en.
,.or(IIBOgINtnoouctton

The iron mines of Brosso and of Traversella(Province of Torino, Piedmont, Italy) are well'known sources of fine minerals developed neartle contact between the Traversella monzonite
stock and.marblesinterbeddedin the mica schistsof the Sesia-Lanzozone.Giussani & Vighi (1964)
described boron'mineralization, with ludwigite
and szaibelyite occurring just at the contact, inmagnetite skarns of the Brosso pyrite mine;
they listed the principal references-concerning
Brosso and Travirsella. The recent discovery ofarsenic minerals is reported by Abbona et al.
(re69).
'In the spring of 1972 Messrs. V. Farina andM. Rapazzini of tle Gruppo Mineralogico Lombardo formd the first specimensof the new mineral at the same locality, level 373 of the Vola
Gera tunnel, after the mine had been abandoned.
Sovrrvrem.e
These were brought to our attention by Dr. V.
de Michele, curator of the mineralogical section
pr6sente
fibressousformedeLa canav6sitesed'un blanc laiteux, groupEesen rosettes dans des of the Museo Civico di Storia Naturale di Milanoskarns i ludwigite et i magn6tite dans la mine de where tylte material is deposited. Since- 1973
fer abandonn6ede Brosso (Pi6mont, Italie). Elle est samplesof canavesitehave been widely collected
monoclinique(symbolede diffraction 2/mP-/-) avec and occasionally traded as nesquehonite.
a 23.49(2),b 6.764(6),c 2l.9lQ)4., F ll4.9l(9)'i
Canavesite (pronounced KANAVEZAI'T) repD.a" t.790 g cm4 pour Z= L2, I-es raies les plus
witl carboborite, CazMg(COsXBrO5)'
resents,intensesdu diagrammede poudre sont: 9.54(100)
10H,O
Qlsieh et al. L964), the only exarnples(202\, 8.12(40)(201), 7.80(1SX102,501),
4.56Q1)(501,503)et 3.1104 (19)(401).rrs fibres sont al- of carboborates.
The mineral is named after the district, Canalong6essuivant [010] et pr6sententun ou plusieurs
clivages {&0/h optiquement elles sont biaxes, 2V vese,in which the village and the rnine of Brosso
trbs grand, Z-b, na 1.485(4), n9 L494(4), n'r occuf, near the town of Ivrea. The name and1.505(2).Les analysesATD et ATP, ainsi que les specieshave been approved by the IMA-Comclich6s de poudre aux rgyons-X d hautes temp€ra- riission on New Minerals and Mineral Names'tures. ont mis en 6videncedes rfuctions de d6compositionqui donnentcommeproduits Mga(BOr),etPARAGENESIS
MgO au-dessusde 800"C. En particulier, IATPde 10, 20, 30,39,43,
montredespertespond6rales
Canavesiteoccurs as milky rosette-like aggfe5A et 56Vod 95, 190,300,410,475,625et 875"C,(Fig. 1) of very thin t0101 elongated figates
respectivement.Ir spectre d'absorption infrarouge69

70THECANADIAN

MINERALOGiST

bution of lamellae around the needle axis (Fig.
2c).T\e habit of the material and its easyalteration, beginning at about 40oC (seebelow), madetroublesome and imprecise the measurement of
the following optical sharacteristics: biaxial
positive, 2V very large, Z=b, refractive indicesq9_1r.gh0 na 1.485(4), nB La94@) and ny
1.505(2); nq. and np actially correspond, respectively, to the minimum (more frequent) andthe maxirnum value observed perpendicular tothe needle axis.
Very rare single crystals with prisrnatic hexagonal habit (Fig. 2d) were observed at higher
resolution only. Fracture leaves uneven sections
asross the fiber axis; along this direction one ormore unidentified {ll01} cleavages or partings (?)
were observed.
The X-ray diffraction pattern of tle fibers
yas very weak; oscillation photographg took noless than jry9 days of exposure to produce patterns exhibiting a mirror plaue coincident *ithtle zeroJayer line and a fiber period of 6.16A.
The corresponding zero-level Weissenberg films
s!9wed, at best, half a dozen faint spots considerably elongated in the or direction; usuallyI A I J L E I . X . R A Y U A T A I - ( ) R( ' A N A ! E s I T E

FIo. l. Rosette-likecanavesitewith spheresof a hydromagnesite-likemineral (see text); scale bar
2mm (photo C. Bevilacqua).
bers on surfaces and along fractures of ludwigite
and magnetite skarns. It seems clearlv to haveformed since mine operations ceasedby reactionof carbonatic solutions with ludwigiie. Canavesite is associated with spheres of an earlierformed mineral upon which the needles may
be implanted (Fig. 2a). The properries of thespheroidal aggregates suggest the unnamedhydromagnesite-like mineral Mgc(CG)a(OH):.
8HrO (Suzuki & Ito 1973) or dyp.ingite Mgc(COa)a(OH)r'sHrO (Raade l97O). Further investigations are in progress.
Pgysrcer, exo CnysrellocRApnrc

hopgnrtBs

F:9- the silky aggregates,fragile bur s[ghtlyflexible ,fibers having vitreous lustre (Fig. 2b)
exteud for about 1 mrn. They show no fluorescence under ultraviolet light; under the polarizing microscope they appeir as flat, colorGss andtransparent crystals with very weak dispersion
and maximu.m cross-sestionof about 5XSO &m.
Uader fts ssanning electron microscope,'thefibers appear as textures with an unev"i dlrt i-d .

r&)
40

9.54
B.r2
?.80

t8
l4
8
2IO
721
712
il
9t9

7.2t
5.40
5.00
4.78
4.56
4.014
3.693
3.332
3. I B{)
3. ilo
2.993
2.889
2.??22.',126
2.690
2.60?
2 . 5 71
2.505
2.407
2.39',7
2.2A2
2.233
2.201
2.147
2.048
2.015
I .949r.910
r .9001.824
I .545

537
2
53t3
6I4

Ave.aS{A)resul!s

fromfllms&la.rir

2oz

9.54
8.08
?.83;?.81
7.45
7.25

201

&2
io3
403
004
203;404
4l0i3l4
511
015i7O2614;606
io?
5 l 2 i l2 l60?i6rl
41?i323
7o7|422603;405
306i322
4 2 1 ; R5lB0l703525;ao6526416506;ll8727
8l3iA28230;820
232i72e534;525
0U:723035
831;23?;038

and cente.

datawilhFcKo

4.97
4.79i4.?7
4.58;4.56
4.030:3.991
3.67?
3.340;3.330
3 . 1 8 8 : 3 .I 8 l
3.t06
2.996;2.988
2.889:2.886
2 .?'74i2 .??4
2.726i2.724
2.693i2.6@
2.61Oi2.60?
2.573i2,5?3
2.505
2.404
2.39812.396
2.243
2.233
2.2O4i2.2O9
2.143
2.051i2.046
2.01712.O15
1 .947i1 .94?
I . 9 13 ; l . 9 1 2
I .899; I .897
1.825
1.589i1.586;1.583

and CuKO

rsdiailons.

CANAYESTTg

A NEW7l

CARBOBORATEno spots at all were detectable. Electron diffraction patterns obtained with the beam roughly
perpendicular to the fiber axis confirmed tle
iep-tition period along this direction and theneedle texture showed by SEM. On tle basisof the fiber period and a few daorvalues measured on oscillation and Weissenberg films, the
X-ray powder spectrum (table 1) was indexedwith a 23.49Q) b 6.164(6) c 2I.9|Q)A I
ll4.9t(9)o. No systematic absenceswere observed; tle space group is presumably one included in the diffraction symbol 2/mP'/-' but
owiug to the scarcity of single crystal data,twinned trislinic symmetry cannot be excluded.
The pseudo-hexagonal dimensions of the cell
could account for the hexagonal habit, which
probably reflects the_presence of tle pinacoids{100}, {001} and {101}.
CorrposrrroNer, Dere

Frc. 2. a. Canavesiteimplanted on a spherical aggrcgat€ of a hydromagnesite-likemineral; SEM,
The infrared spectrum of canavesite (Fig. 3)
scale bar 0.05mm. b. Close view of a rosette;
is not easily comparable with those of wellSEM, scalebar 0.1mm. c. Needle texture; SEM,known families of minerals; broad and strong
scale bar 0.01mm. d. Single crystal with hexabands near 3500, 1450 and 1000 cm-l could begonal habit (only two faces are visible); SEM,
interpreted as due to OH-. COa, and, with greater
scalebar 0.005mm.
uncertainty, to BOg&.The products of heating to90O'q after 56Vo weight loss, were identified
as a mixture of Mes(BOg): and MgO (Iable 2). 1.908 and of. 1.92I rdth the specific refractive
Canavesite effervesces with dilute HCI at energies reported by Larsen & Berman (L934)
room temperature. The chemical analysis,made and by Mandarino (L976), respectively.-The
by a combination of severalmethods on 100 mg discrepancy between Do"r" ood D/"ur", which reof fibers selected under the binocular microquiresZ=L3, can be ascribedto severalindepenscope,is given in Table 3. On the basis of eleven dent or concurrent causes' e.g., imprecise reoxygens the analytical formula is Mgr.or(CO')'.0'- fractive indices, minor content of water, disorder(IIBOs)o.ga'4.91Hro, ideally M&(COaXHBOg)' in the crystal structure with a fractional Z in
5HrO or, perhaps, Mg:(CO",HBOs)g'5HzO.
the cell.
Because of tle habit of the material, only anapproximate measurement of the density was
Ttrrnrrter, SresnrrY
possible by the heavy-liquid method; the value,
idealizedg
12tequites
cma'approximately 1.8
The TGA curve @ig. 4) has inflections at 95,
unit formulae in the cell (D""r" t.790 g cff; V
2877.3if; M.W.258.559). For the ideal fortnula 190, 300, 4LA,475, 625 and 875oC, which corthe Gladstone-Dale law suggests a D'.a' ot respond to oumulative weight losses of L0, 20,m^&zEeEo:
2Ia,*iffi,oleuml@@&@Flo. 3. Infrared spectrum of canavesite;0.6mg in 100mg KBr disk'

72

THE

IA&E

CANADIAN

2. X-RAY POWDERDATA FOR PHASESOBTAINEDBY HEATING CANAVESITE

IIill

@90cc

s-1650c

16r2756C

2?r5250C

d(A)

d{A)

d(A)

dG)

r

7.55 m
4.93 s4.19 vw
3.St
3.Sw
3..m nw
3.mw
2.940 va
2.895 vr
2.Wns
2.4Y nft
1.941 vw
1.906 vrl.S0 wr

7.13 mw
4.93 s4.20 vw
3.53 r
3.$vw
3.6or
2.97An2.943 ms
2.SB r2.gms
2,429 tue
2.C? vsMINERALOGIST

VI

I

3.!
m
2.9Sm!
2.5$ms
1.?33 s1.4& vw|

4.ZO fr
3.76 w
3.53"
3.48 m2.951 s2.Sms
2.398 mgl.?49,
1.92 ss2r?goocd{A)Id(A)3.98 v*
3.75 v$
3.63 m3.9vw
3.€m
2.953 s2.741n b
2.&1 s
2.459 vw
2,429 ns .
2.1S ns2.127s &(Nonlus) .ador6,tulnl€.-Lenn6
CuKa radlalid;
mdtm6
mossu.St6s€w€ak, mEmdl@,
sq3!fon9, vrsvery we€k, v6Eve.y 5!ron9.
a-M93(BO3)2, b-MqCO3,c-M€.

d4

7Sto&ocI

r.S0 vr
1 . 9 3 1v * b
1.s2 !ft1.818n1,143,
1.708* b
1.659 vt
l.559vr
1.522 s1.502 m ci.6? v*
l.457vrl.gw
bd(A)r4,r.8 n
4.@ va3.17 !83.52 ns a
3.25 ms €2.962vs2.?&!*
2.1OAv. a2,82 vw
2.521 nH a2.&sc
2.A7vsaz.Wms
a2.gra2.28ea2.201 sa2.1S vs €c
2.0S s
€2.055 vw ad(A)I

2.m5 vw al.Mvrl.&

ns 6al.@ vw a
1.&2 ln a
1.59 s6
1.5?3 mw a
l.5gm
l.Ws
1.490waac
6

1.379 w a
1.373 mw €1.3& w €i30, 39, 43,5A and 56/o rcspectively;secondary der), 260, 325,
35MOO and 480-600 (broadeffects are indicated by the derivative'curve oniy p?\.),
665, 7'0Oand 790-840'C (broad peak).
at 45,365,475,650, 690, 760 andThe complexity of the thermal behavibr of!1gt^r:po-rted)
825"C. With some approximation the above canavesite
is confirmed and in part clarified bytemperatures reflect endothermic reactions in a continuous
X-ray powder spectrum Cfable j)
the DTA pattern (Fig. 4), where effect$ occur taken
between 20 and 1050.C. The unambiguat 80, 1O5and 125 (shoulders), t7S, LgS (shoul- ously
identified phasesMgCOs and MgO appear
near 530o-C;Mgr(BOr), and MgO aie pidsent
above800oC.The range 165-530.C is characterized by poor crystallinity (unidentified X-raypatterns III and IV in Table 2). In the range
4O-165"C, X-ray patterns I and II differ only intheir first reflection, and differ from that ofcanavesiteby shifts, mainly towards higher angles, of the majority of the lines. phases I andII could represent partly dehydrated canavesite,with 2 and 3 water molecules lost, respectively,
T A B L E 3 . C H E M I C A LA N A L Y S I S

MsO

31.50"

31.?0uBzo:

r2.8oo1z.6obaoz

t8.g3t19.32'Hzo

32.56"

37.32"

Total

100.69

99.94

31.60
tz.zob56.ooo

31.21

r2.?o

13.40

18.57

i7.03

3?,44

38.35

100,31100.00D. Avenagevaluesof the analysesA, B andC.
E . M g ^ ( c o ^ () H B o - ) . s H ^ o .
zJSZ

Fro.-4.TGA (top) and DTA (bottom) curves;10mgof canavesitewith l0 and 20"C/min. sp""d, ,e_spectively.

a. Colorimetry.- b. Tltraiion with NaOH of a HCI solulion lnp n e s e n c eo f m a n n i t o l . - c . C . E r b a 1 1 0 4e l e m e n t a lm t c r o a n a l v s e r . d. Total wt. loss at 900oC.

CANAVESITE,A NEW

but witlout a breakdown of the crystal structule.
Breakdown surely occurs in the range of low
crystallinity q/ith, firstly, the complete loss ofILO below 300'C and, subsequently'at around
400oC, of OH-. The presenceof MgCOa in pattern V (fable 2) shows that the loss of COroccurs only after complete dehydration.
The stability field of canavesite confined belcvw 40oC and its occurrence on surfaces in atunnel of an abandoned mine clearly show thatthe mineral formed at or near room temperature.

AcKNowLBDcBMENTS

The writers are grateful to Messrs. V. Farinaand M. Rapazzini who made samples available
through Dr. V. de Michele, to Mr. G. Maletto
who sacrificed perhaps the best specimen of ca'nayesitefor this project, and to Dr. A. Kato forhis stimulating criticism. To Dr. V. de Michele
we are indebted too for his continuous interestin the work and for suggestingthe mineral name.
The electron microscopy and diffractornetry
were performed at the Centro Ricerche FIAT(Orbassano, Torino) through the kind interest ofDr. G. Ma.nnone.Researchwas supported by theConsiglio Nazionale delle fucerche, Roma.

73

CARBOBORATB

RBreneNcBs
ABBoNA, F., Cor"reecNoNr, R. & FgRRARIs, G.
(1969): Contributo alla conoscenzadi min'erali arsenicali. Nota I. Ricerche su nuovi minerali diBrosso (Iorino). Period. Mineral. 38' 245'284,
GrusseNr, A. & Vtcru, L. (1964): Caratteristiche egenesi dei minerali di boro ludwigite, ferroludwigite, szaibelyite e camsellite della miniera diBrosso (Iwea). Period. Mineral. 33, 471-500.
HsrBn HsrrN-Te, CruBN TzB-CrueNc & Cru L.lr-P"lo(1964) : The new mineral carboborite MeCag(COJ(BaOs)'10HrO. Scientia Sinica 13, 813-821'
LensBN. E. S. & Benrvralq,H. (1934): The microscopic determination of the nonopaque minerals'
US. Geol. Surv. Bull. 848.
MrNoenrNo, J. A. (1976): The Gladstone-Dale relaI: Derivation of new constants.
tionship-PartCan. Mineral. L4, 498-502.
Raeor, G. (1970): Dypingite, a new hydrous basic
carbonate of magnesium from Norway. Amer.
Mineml.55, L457-1465.
Suzun, J. & Iro, M. (1973): A new magxresium
carbonate hydrate mineral, Mgs(COs).(OH)z'
8H2O, from Yoshikawa, Aichi Prefecture, Japan.
J, Japan, Assoc. Mineral. Petrog. Geol. 68, 353361
Received lune 1977; revised manuscript accepted'
Oaober 1977.