Canadian Mineralogist
Vol. 18, pp. X97-200(1980)GAITITE, HgGagZn(AsOn),(OH),,A NEW MINERAL FROM TSUMEB, NAMIBIA(sourH wEsTAFRIGA)

B. DARKO STURMAN
Departrnerrt of Mineralogy and Geology, Royal Ontario Museum,
100 Queen'sPark, Toronto, Ontario MSS 2C6PETE J. DUNN
Department of Mineral Sciences,National Museum of Natural History,
SmithsonianInstitution, lilashington,D.C. 20560, U.SA.
b 7.61(l), c 5.57(1).4"a 111040(5)',p 70o50(5)',v 119"256)'i Doarn= 3.80 Pur Z = l, D'"" 3neuf raies les plus intenses
3.81(5). ksdu clich6de poudresont (4 I, hkl): 5.05(40)(100)'(50)(020),( 110. 3.208
3.5SI (40)( 121), 3.350(50)3.0s0(80)(Tll), 2.7sL0oqQh,1I1), 2.7s|(7D',)(11D, 2.r6s(4u1l2) et r.72r(6o) 4,.
Cfraduit Par la R6daction)

ABSTRACT

Gaitite occurs as coatings and as small crystals onprosperite, adamite and austinite on specimens from
Tsumeb, Namibia (South West Africa). Gaitite iswhite to colorless with vitreous lustre; white streak;hardness (Mohs) 5. Cleavage is good on {010},{001} and {0I1}. Gaitite HgCazZn(Aso4),(oH),and talmessite HzCagMg(AsOn)r(OH), are isostructural and form a solid-solution series. The indicesgaitite, Tsumeb, Namibie, ars6niate,nouof refraction of the zone with the composition H:.oo Mots-cl6s:
velle espdcemin6rale.
(AsOn)r.oo(OH) r.oo
Ca1.rr (Zno.s0Mgo.reFeo.orMno.ot)
are a 1.713(2), P 1.730(2). r 1.748(2'); 2l/'l88"; the orientation of the indicatrix is X (6 - 28",
INnoPucrtox
p - 32o), Y (6 : 185o, p = 60") ao.dZ (6 -79"_, p - 80o). Gaitite is triclinic, space group pl
During the study of prosperite (Gait et al.
or Pl. Cell dimensions. similar to those of F -roselite 1,979), another phase found on the type speciand talmessite,are a 5.90(1), b 7.61(l), c 5.57(l')
men from Tsumeb, Namibia (South West AfriA; c 111o40', F = 70"50', v ll9o25', atl !
5';sa) . was tentatively identified as talmessite,
D."t. is 3.80 g,/cms for Z = 1, D."* is 3.81(5)HzCazMg(AsOo)z(OH)a.However, an examinag/cm8. The strongest nine lines in the X-ray
tion of the optical properties indicated that apowder-diffraction pattern are: 5.05(40)(100).
3 . 5 8 1 ( 4 0 ) ( 1 2 1 ) ,3 . 3 5 0 ( 5 0 () 1 l Q , 3 . 2 0 8 ( 5 0 ) ( 0 2 0 ) . large proportion of Mg must be replaced by( l 11), 2.78r(1AO)
3.080(80)Qzr,rrr), 2.7sO(70) another element, later identified by X-ray fluo(TD,2.r6s(4c)(o.5Dand1.721(60)A.
rescenceas Zn. Subsequentmicroprobe analysis

confirmed this observation and also showed thatthe grains are strongly zoned with large variations in the Mg:Zn ratios.
Sot"lNrerns
We take pleasure in naming this new mineral
speciesin honor of Dr. Robert I. Gait, Curator
On trouve la gaitite en enduits et en petits cristauxof Mineralogy at the Royal Ontario Museum.
sur prosperite, adamite et austinite sur des sp€ciWe do so in recognition of his contributions to(Afriquemens de Tsumeb, Namibie
du Sud-Ouest).
mineralogy (in particular his curatorial excelC'est un min6ral blanc i incolore, I l'6clat vitreux,
rayure blanche, duret6 Mohs de 5 et bons clivages lence) and his many exhibits explaining the{010}, {001} et {011}. La gaitite HzCa,Zn(Asoa)g concepts of mineralogY.
(OH)z et le talmessiteHgCarMg(AsOa)g(OH)n forThe name and the mineral have been apment une solution solide compldte et sont donc iso- proved by the Commission on New Minerals andstructurelles. Les indices de r6fraction de la zone Mineral Names, I.M.A. The name is pionounced(Zns.66Mgs.1*Feo.ntMrlo.ot
de composition Hg.ooCar.ge)
GET'AIT. A type specimen, containing about(AsOa)z.oo(OH)e.oo
sooti a L.713(2), p 1.730(2),'{50 mg of gaitite, is preserved in the Royal
1.748(2),2Vt 88': l'indicatrice a l'orientation X (6Ontario Museum, Toronto (M35388). A pol28", p 32"\, Y (6 185o, p 60o), Z (6 :79",
p 80o). Triclinic: le groupe spatial reste ind6ter- ished thin section of the grain analyzed by
microprobe has been registered at the United
min6. Les dimensions de la maille ressemblent iStates National Museum of Natural History,celles de la F-rosdlite et de la talmessite: a 5.90(1),Keywords: Gaitite, Tsumeb, Namibia, arsenate, newmineral description.

I97

198

THE

CANADIAN

MINERALOGISTCRYSTALLOGRAPHY
Smithsonian Institution, Washington, D.C.
(NMNH t44799).
Gaitite is developedmostly as a polycrystalline
The strong Mg-Zn zoning indicates complete
solid-solution between gaitite HzCaeZn(AsOo), coating; only a few small crystals were fo rnd,(oH), and talmessiteHzcaeMg(Ason),(oH),. with the largest dimension of about 1 mm. The
The name gaitite is to be used for members in facesof onlylour forms were observed.The edges
between the well-developedfaces t010), t001)
which Zn predominates.
forthenameand {0T1} enable one to find the a axis on theThere is some confusion about
the Mg end-member.Two names,talmessiteand crystals or fragments; the face of {100} is usuallyarsenate-belovite,have been used. The first, and verv small.
ihe crystals were first examined with the two'
unfortunately incomplete, description of thegiven
bycircle opiical goniometer. Then, the unit- cell,
phase H,CazMg(Asoe):(OH), wasNefedov (1954), who proposedthe name belov- similar io thai given for talmessite, was foundite. However, the name belovite was also given on the projections of the 0 and 1 levels of theto the Sr analogue of hydroxyl-apatite, de- reciproc-al lattice, prepared from Weissenberg
scribed by Borodin & Kazakova (1954).
Yakhontova & Sidorenko (1956) proposed TABLE2. X-MY POI.IDER-DIFFRACTIONDATAFORGAITITEANDTALMESSITE
that the name arsenate-belovite be used for the TALMESSITE,OAITITE
mineral with the compositionHrCaeMg(AsOa), JCPDScard fl7-164wLdcalc
dr"a,
Idt"u,
I(OH),, and the name phosphate-belovite forstill
incomplete,
wereSr5(Po4)s(OH). The data
6.4'14010
20
6.40
o.qJ
lI05 .1 6 7
5.08(noI r0
and it had not been determined whether arse- OU
5.054
t00
5.05
t40
'rIl
roselite
4.
6404.
6420
tomonoclinic
4.
6240
nate-belovite belonged the't0l
3.964
3.958
5l
0
gtoup or to the triclinic B-roselite group.
rZl
3.583
40
3.581
600ll
3.572
30
3.570
Bariand & Herpin (1960) describeda triclinis
6
3.44
lt0
3.343
50
3.350
3.3440modification of HaCa,Mg(AsOo)a(OH)", from
2 ?n4t ?nnTol
Talmessi in Iran, that is isostructural with B020
3.207
3.208
50
3.2180
oZt
3.088
3.098
I30
roselite, HrCazCo(AsOe)r(OH)2,and they used 1 0 0
3.07
Irl
3.077
3.080
t80
2Il
2.842
2.838(1964),
the name talmessite for it. Later, Pierrot
lll
2.810
2.815
221
I 2.782
after studying the Epe material of both talmes'z't6tr r00
lll't00
I z.zgo2.77site and arsenate-belovite,showed that they are
r122.
7462.
750
[705the same species. The name talmessite is now
0i22,602
2.607
130
2.58
20220
2.583
2.582
used by most mineralogists; in 1976 the Comtl0200[ 2.527
a Ed
6dl0
2.51
mission on New Minerals and Mineral Names,
r3rt 2.516
2Ql
2.447
10
2.445
2.
4
420
I.M.A.. officially approved its use.
I30
2.357
2.356
I'I.
TABLE

ANDOPTICALDATAFORGAITITE
CRYSTALLOGMPH1C(As0n)r(0H)2
HZCaZ(zn..
l4Feo.o,,ltlno.
ot )B4MsO.

UNITCELL:Spacegroup P] or PIi Z E 1d r n ns . 0 5 ( l ) A
a . 5.90(l)AB
rr {I00.}o:
I ror
toortIFoms

I t o l ])J:

Princl pal
Vibratlon
Dirstlons

lrIz

2.16

5
10

2.1?
2.07
2.O475"20(5)'

2020

2.01
l.B9
1.86
1.829

Br 100.30(5)'rr 65'05(5)'2060

1. 7 8 2
1. 7 1 740| .697

'10

1.608
1.584

o*

lll'40(5)'70"50(5)'ll9'25(5)'COORDIIIATES:

40

a n i ie . e r t r ) A
20aii, s.ostt
lA
20, " 7.61(1)Ao - 5.57(l)Ao5Op
65"05',

90"00'0'00,90'00'- 5f'29'

23"57',
33'59'

211'0r'
28"

32"

185'
- 79'

60'
80"

OPTICAL
DATA:
o

1.713(2)2V, = 06121'tt"u"''r1.148(212v" = 89'(calc.)

540
5
530
l0
l02030]0
10
l0
1560
2030
5520
l0
5

1.5J6

10
55
l05
l0
5

2.303
2.165
2 . 13 52.118
2.07'l
2.039
2.022
2.010
I.892
t.870
1.829
1.8011.782
1.721
1.712
1.700
1.688
|.601
I.581
1.555

||

2.336
2.320
2.3U
z. too

2tr1

222
120
I32

t.l4a

1.538
I .521
1.492
1.461
1.432
1.407
I.390

Rlt?o5

1.242

Gulnier-de Colff cmera, Cul.€radlatloni intensltl€s estimatedvlsually; d. double.

GAITITE. A NEq/ MINERALFROM TSUMEB

199

photographs. The rotation- and precession-samera methods were used to complete the singlecrystal study reported in Table 1.
The X-ray powderdiffraction pattern was indexed using the unit-cell dimensions determinedby the single-crystal methods, and the intensities
observed on films prepared by the single-crystal
methods. In Table 2 the indexed pattern for
gaitite is compared to the pattern of talmessite.
The indexing for gaitite does not agree entirely
with that of talmessite (c1., PDF 17-164).
Puvsrcel euo Oprlcel Pnopnntras
The small grain size and zoning made an
accurate determination of density nearly impossible. Density was determined by heavy-liquid
methods on a small crystal fragment that waslater analyzedwith the microprobe (Table 3).
Examination of the indices of refraction showedthat the major part of the fragment is homogeneous.The measureddensity, 3.81(5) g/cms,compares well with the calculated density of
3.80 g/cms for gaitite with the composition given
in Table 3. The Mohs hardnessis approximately
5.
Cleavage is not easily observed, but there areprobably three equally good cleavages, {010},{001} and {0T1}. Most gaitite fragments havean irregular outline with only one or two cleavages visible.
Gaitite is white to colorless; the lustre isvitreous and the streak is white. The opticalproperties were determined on the fragmentsthat were analyzed with the microprobe. Optical
data for the zone with the composition of(AsOa)r(OH)r are
HrCaz(Zno.arMgo.raFeo.orMno.or)shown in Table 1 and Figure l.
Indices of refraction and indicatrix orientation
were determined with the spindle stage in Na
light on an analyzed grain that was oriented
by X-ray single-crystal methods. The optic axial
angle was determined on the universal stage.
TABLE3.

MgoCaoznoFeollno
As-o.
aaHzO
TotalFlc. l. Stereographicprojection of optical andcrystallographicelementsof gaitite.
It was impossible to determine accurately therelationship betweenthe Zn:Mg ratio and opticalproperties because of the strong zoning andsmall grain size. A zone with Zn:Mg - 1:1 is
optically negative, 2Vn = 85(5)', and q,1.689(4), B 1.707(4) and y 1.727(4). Replacement of Zn with Mg seemsto lower the density,
decrease the indices of refraction and change
the optic axial angle to a negative value. The
orientation of the indicatrix in the zones withdifferent Zn:Mg ratios is nearly identical, as isindicated by nearly identical extinction for allzones.
Gaitite does not fluoresce in either long- or
short-wave ultraviolet radiation. The GladstoneDale constantKc (Mandarino 1976), calculated
from the chemical composition given in Table 3,
is 0.188, which compares well with the value
Ke - O.192, calculated from the measured density and indices of refraction
CneMrsrRY

MICROPROBEANALYSIS
OF GAITITE

Analysls
1.2
24.2
15.3
0.2
0.2
5O.2
7,8

Theory,r-l

I 00.00

0.024,421 7. 7 1
0.0
0.0
50.04
7,83

:39 of the amountpresent.

Accuracy of data:'HrO
detemined by DTA/IGA

Enplrlcal fomula calculated on the basis of 10 oxygenatms:
Hz.ooet .gg(zno.goMgo.
2.0o(0H)2.00
r4F"0.orho. or )xr .02(As04)

Crystals of gaitite were analyzed using an
ARL-SEMQ electron microprobe utilizing an
operating voltage of 15 kV and a sample currentof 0.15 p,A. The data were corrected using
Bence-Albee factors. The standards used foranalysiswere fluor-apatite for Ca, synthetic ZnOfor Zn, synthetic olivenite for As, manganite forMn and hornblende for Mg and Fe. A wavelength-dispersive scan indicated the absence ofany elements with an atomic number above 9,
except those reported here. The analysis (Table200THE

CANADIAN MINERALOGIST3) is in good agreement with the theoretical ved. Gaitite is followed in the sequenceof for'mation by euhedral crystals of light green austincomposition.
Mettlerite, yellow barite and colorless to light pink
DTA/TGA were performed with aThermoanalyzer on 16 mg of material. The qaartz, in that order.
accurate Mg;Zn ratio of the grains used for
ACKNowLEDcEMENTS
analysesis not known, but it is probably similar
to that of the grain analyzedwith the microprobe
The authors are grateful to Mr. Prosper J.
(Table 3). The grains used for DTA/TGA
were separated with heavy liquids and later Williams for bringing the mineral to their attenexamined on the microscope in the immersion tion and for donating the type specimen to theliquids to ensure that major parts of the grains Royal Ontario Museum. We thank Dr. Paul
have density and indices of refraction similar to Keiler for allowing us to describe his specimen
those of the grain analyzedwith the microprobe. of gaitite. We also thank the following people
A total weight loss of 7.8% is related to two at the Royal Ontario Museum: Dr. J.A. Mandaendothermicpeaks,at 470 and 513oC, indicating rino for discussionsabout the use and the calthat the water content can be expressedashydrox- culations of the Gladstone-Dale constants, Mr.
yl in the formula. We do not have any addilional R.A. Ramik for performing the DTA/TGA'evidencethat hydroxyl and hydrogen are present, Mrs. Cynthia Peat for preparing the X-ray
but propose to write the formula in this way powder-diffraction patterns, Miss Helen Driver
until the structure is solved or IR analysis is for typing-for the manuscript, and Mrs. Josephine
iyping the tables. We thank Associate
Galt
isimpossible
however,
itmade. At the moment,
to select enough material for IR analysiswithout Editor Dr. J.L. Jambor and the referees for a
critical reading of the manuscript and for many
destroyingthe type specimen.
The empirical formula calculated on the basis useful comments.
of O = 10 from the composition given in Table
3 is H:.ooCar.re(Zno.ruM&.rnFeo.orMno.or):=r.o:(AsOr)
REFERENCES,.oo(OH)r.ooor, ideally, HzCar(Zno.aeMgo.raFoo.or
P. & P. Hrnrrw, P. (1960): Un ars6niate
BARTAND,(AsOn)r(OH),.
Mno.or)et de magn6sium, isomorphe de ladecalcium
present
The gaitite crystals examined in theg-ros6lite. Soc. frang. Mindral. Crist. Bull. 83,
study are strongly zoned. The solid.solutionl 18-121.
series between gaitite and talmessite extends atM.E. (1954): Belovite least from Zn:,Mg 86:14 to 36:64. In general, Bonoorx, L.S. & Kazerove,an alkaline pegmatite. Dokl,frommineral
anewthe Zn-rich zones occur in the centre of the96, 613-616. Abstt.: Amer.
Akad. Nauk ^S.S.S.R.
crystals.
Mineral. 40, 367 (1955).
Gerr, R.I., SrunulN, B.D. & DUNN, P.J. (L979):
Prosperite, HCaZnz(AsOn)r(OH), a new mineralfrom Tsumeb, South West Africa (Namibia).
Gaitite was found on the specimen fromCan. Mineral. L7' 87'92.
Tsumeb, Namibia (South West Africa) on whichMeNoenrNo, J.A. (L976): The Gladstone-Dale reprosperite was first identified. The associatedlationship. I. Derivation of new constants. Can.
minerals on this specimenare described in detail
Mineral. 14, 498-502.
by Gait et aL (1979). Ghitite is one of the lastNrreoov, E.I. (1954): Report on nelrt minerals
minerals formed and is developedas a very thin,
discovered by him. In The Scientific Session ofpolycrystalline coating on prosperite, adamite
the Federov Institute together with the Alland conichalcite. The matrix of the type speciUnion Mineralogical Society (V.A. Mokievski,
men of gaitite is strongly altered chalcocite.
ed.), Zap. Vses. Mineral. Obshchest. 82(4), 3lI'
Subsequentto its characterization as a species,
317. Abstr.: Amer. Mineral. 40' 55 (1955).

AssocrerBo Mlxenars

gaitite was found independently by Dr. Paul
Keller of the University of Stuttgart, Federal Republic of Germany. Through the courtesy of Dr.
Keller, we describe here the paragenesison hisspecimen,which is different tlan that on the typespecimen: the matrix is a severelyaltered chalcocite, coated liberally with the alteration product,
conichalcite. The conichalcite is covered by massive, polycrystalline gaitite with a maximum grain
size of 0.5 mm. No euhedral crvstals were obser-Ptrnnol R. (1964): Contribution b la mindralogie
des ars6niates calciques et calcomagn6siensnaturels. ,Soc.frang. Mindral. Crist. BulI.87, 169'2L1.
YAKHoNrova, L.K. & SmoneNro, G.A. (1956): A
new mineral - arsenate*belovite. Zap. Yses.
M ineral. O bshchest. 85(3), 297-302. Abstr,: Amer.
Mineral. 42, 583 (1957).
Received December 1979, revised manuscript accepted February 1980.