I Figure1). Form {121} is a rare form, of rank 21 in order ofincreasing rarity (Bach, 1926), and is only mentioned
herebecause the faces are comparatively
large, give good signals
on the goniometer,and would have been expected to demontrate the tetartohedrismof wulfenite. However, instead ofoccurring on alternate corners only, it is present on all fiveorners of the measured crystal (the remaining three corners
are not present, being in contact with the matrix); a possible
explanation is that both right- and left-handed forms are repreented, of equal perfection and development.
Tetartohedrism,illustrated in the figure, is shown by the shape of the pits
nm{llO}, and by small dull areas on the facese{1l2).
Measurementsof the angles, 10 in all, between faces of {Oll)and between faces of {112), lead to values of 65°49.5' ± OS,
5°49.3' ± 0.3', and 65°49.2' ± 0.6' for the fundamental angle,nd 2.2275 ± 0.001 for the axial ratio cia. Williams (1966) has
lotted values of cia against content of Cr, As, Y, and W in
ulfenite, and shows it rising slowly from 2.2268 to just over_.228 as the W content arises to 1.1%, thereafter(perhaps)
Jropping very rapidly with further increase in W content. Ouralue is entirely consistent with Williams' results. X-ray powder
hotographs of the Tsumeb material are a perfect match forulfenite, and do not show the strong line at 4.96A whichrves to distinguish stolzite (PbW04) from wulfenite,andhich is present as a weak line in the pattern of a specimen
f "chillagite" from Chillagoe.

The crystals are strongly, but irregularly, zoned. A browncore is overlain by blue wulfenite around the prism and lower
pyramid, while the tips of the crystals and perhaps the wholeouter surfaces are essentially colorless. Internal reflections
show flaws round the core material, but the detail of the color
distribution is obscured by the high refractive index and thebrilliant luster of the faces. Small rough crystals on the matrix
are pale blue or colorless. The material has been examinedby electron microprobe in both laboratories and, although Ca,As, Cr, Y, Ti, and W were looked for as minor constituents,
only W was detected. About 1.3% W03 was found in the Smithsonian specimen, and 0.25% WOs in a fragment of BM 1976,
108. The latter, about 10 x 8 mm, showed all three colors but
there was no detectabledifferencein composition
betweenthem. It seems probable that the blue color is caused by partial
reduction of Mo6+ to Mo4+ (compare ilsemannite).
We thank Paul Hicks, BM(NH), for the crystal drawing.
References
BACH, L. (1926) Ueber
380 - 419.

MINGA YE, J. C. H. (1916) Notes
New South Wales, 9, 171.
ULLMAN,Abstract
Keyite, (Cu,Zn,Cd)3(As04)2,
occurs as small blue prisms
n cavities in tennantite ore from Tsumeb, Southwest Africa,
sociated with cuproadamite(Cu:Zn 3:2) and schultenite.
Microprobe analyses gave CuO 18.81, Zn 17.90, CdO 14.08,
PbO 0.63, CaO 0.80, MnO 1.07, AszOs 45.36 (means of 6 anal. es on 5 crystals), Sum 98.66%. D obs n.d., but>
4.2. Cell'on tents for 48 oxygens 6[(Cu,.,gZn,.nCdo'55Mno.osCao,o7Pbo.o,)sum 3.o,As,.ggOs], ideally 6[(Cu,Zn,Cdh(As04hlwith Cu:Zn:Cd'lear 2:2:1, for which Deale = 4.95. Soluble in cone. HCl or
HN03, no water detected, blackens on heating. Monoclinic
12. Im, or 121m; a 11.65, b 12.68, c 6.87 A(± 0.01), (3 98.95°::!: 0.05 0), Y 1002.5 A 3. Strongest powder lines 3.29 vs(2), 2.876\s(3), 2.795 vvs(1) (Cu-Ke): 48 lines recorded.
Crystals prismatic [001] to tabular {01O}, commonly taperingor showing sub-parallel
stacking on {01O}. Dominant
forms
observed on SEM photos {01O), {1l0}, {210}, [Ol l}, and perhapslOl}. Cleavage {001}, good. No twinning observed. Color deepsky-blue, streak pale blue. H 31/2 - 4. Biaxial, sign and 2V not
determined,
optic axial plane {01O). a 1.80, {3 n.d. (= b),y 1.87. Strong dispersionof indicatrix: a:[OO11 101/2° (Cdred), 1)1/2 ° (Hg yellow), 121/2° (Hg green), 91/2° (Hg violet).

Jahrb. Mineral., B.-B., 54,
on chillagite.

Rec. Geo!'

A. T. (1912) A new mineral. Journ. Proc. Roy. Soc.

New South Wales, 46, 186.
WILLIAMS, S. A. (1966) The significance of habit and morphology of wulfenite. Amer. Mineral., 51,1212 -1217.

Keyite: a new mineraljrom
byPeter G. Embrey, Eva E. Fejer, and Andrew M. Clark
Department of Mineralogy
British Museum (Natural History)
Cromwell Road
London SW7 5BD, England

Wulfenit.

TsumebNamed for the mineral dealer Charles L. Key, who supplied
the mineral for investigation.
Name approved by IMA Commission in 1975. Type specimens in BM(NH).
Occurrence
Keyite was brought to our attention by Charles Key, whosubmitted for identificationsome minute blue crystals nestlingat the base of much larger « 2 mm) crystals of cuproadamite
on a matrix of tennantite. Since the specimen was from Tsumeb,
we at first suspected the crystals of being stranskiite (triclinicCuZnZ(As04)2; Strunz, 1960), for which no powder data have
yet been published. However, on discovering major cadmiumin our mineral and establishing its symmetry as monoclinic,
we became convinced that we were dealing with a new species.
Stranskiite occurs on chalcocite at the 1000 m level at Tsumeb,
but we have noinformation
about which part of the mines ourspecimens came from.
Cuproadamite,the copper-rich variety of adamite, as small
but abundant green prisms, has been associated with keyite
on all the specimens we have seen, and it was the only otherarsenate present on our original specimen (BM 1973,236). A
subsequent specimen (BM 1975,660), first loaned by and later
acquired from Mr. Luis Teixeira-Leite,carried large (ca. 2 em)
prisms of schultenite as well. The unusual habit of this newschultenite
is the subject of a short note elsewhere in thisvolume. Keyite and cuproadamite
appear to have crystallizedmore or less at the same time, since the keyite sometimes sitson and is sometimes partly enclosed by cuproadamite.

87

Table 1. Keyite:

microprobe

analyses

12

3

4

5

6

Mean

19.23
17.94
13.98
0.14
1.11
1.27

18.76
18.14
13.58
0.40

20.22
17.59
13.64
0.62
0.83
1.07

16.84
18.57
14.93
1.42
0.41

19.80
16.78
14.59
0.65
0.97
1.21

18.01
18.41
13.78

18.81
17.90
14.08
0.63
0.80
1.07

CuO
ZnO
CdO
PbO
CaO
MnO
AS205
Total

45.54
99.21

Cations

calculated

Cu
Zn
Cd
PbCaMnAs(Sum)

1.209
1.102
0.544
0.003
0.098
0.089
1.982
3.045

0.91
1.16
45.40
98.35

45.57
99.54

0.94
45.02
98.13

44.96
98.96

0.55
0.59
0.79
45.68
97.81

1.084
1.169
0.596
0.033
0.037
0.068
2.006
2.987

1.258
1.041
0.574
0.015
0.087
0.086
1.976
3.061

1.148
1.147
0.544
0.013
0.053
0.056
2.015
2.961

45.36
98.65

1.193
1.110
0.554
0.014
0.072
0.076
1.992
3.019

to 8 oxygen atoms
S.D.
1.189
1.124
0.533
0.009
0.082
0.083
1.9923.020

1.271
1.076
0.531
0.014
0.073
0.075
1.983
3.040

0.070
0.047
0.026

0.015

Columns 1 & 2, one crystal from 8M 1973,236: columns 3 - 6, four crystals from 8M 1975,660.
S.D. = standard deviation (major cations only).

Chemistry
There is too little keyite for a full wet microchemical
analysis,so all the analytical work has been done on a Geoscan electronprobe microanalyzer.
Element scans on a grain from the original specimen showed the presence of major Cu, Zn, Cd, andAs, with minor amounts of Pb, Ca, and Mn; this was confirmed
later on grains taken from four other specimens loaned to us.
Six quantitative
analyses were performed,two on opposite
ends of a single grain from the original specimen and the remainder on four separate grains from a second specimen (table1). Anglesite and wollastonite
were used as standards for Pband Ca, and pure elements for the others. Assuming Z = 6(see below), the mean of the six analyses leads to the formula6[(CUl'19Znj.nCdo.55Mno.osCaO.07Pbo'Ol) Slim 3'OlAsl.990S], idealizing to 6[(Cu, Zn, Cd)s(As04)2],
with Cu:Zn:Cd nearly 2:2:1.
The three principal cations show only a limited tendency toreplace one another in the grains examined,with standard
variations of 4 - 6%. It is interesting to note that, despite theevidence that keyite crystallized at about the same time, optical
spectrographyof the cuproadamite
showed no trace of cadmium. This suggests that cadmium cannot be accommodated
in the cuproadamite
structure. A survey of several different
specimens of cuproadamite
shows considerable
variation inthe Cu:Zn ratio, but the crystals associated with keyite have
Cu:Zn near 3:2; we are continuing work on this problem.
Keyite is readily soluble in concentrated
acids. Tests for thepresence of water were made, but no water was found; themineral blackens on heating, and presumably loses much of
the arsenic.
Crystal geometry
Single crystal rotation and Weissenberg X-ray photographs
show keyite to be monoclinic, with a body-centeredunit cell(systematic absences for h -l-k +1 odd). The space group possibilities are thus 12, Im, or 121m, but we have not tested forcentrosymmetry.
Unit cell dimensions are given in Table 2, and88

were refined from the powder data in the same table using theWeissenberg
data in the indexing. Calculated
d-spacings are
not listed, but they are in close agreement
for the assigned
indices.

bhm//

Figure 1. Idealized drawing of keyite, showing forms h r2101,m {110}, b rOIO], and q [011].

Figure 2. Keyite crystals showing forms h[2101, ml l lfl}, b[0101,and q[OllJ; the largest crystal shows the terminal form [201 ](? l. SEM, SOOX.

Figure 3. Keyite: a typical sub-parallel group of crystals. The
apparent size of (011):( 011) is increased by divergence. SEM, SOOx

The specific gravity is greater than 4.2, shown by crystals
sinking in Clerici solution, but we were unable to measure it
more accurately than this. To obtain a density of this order,
bearing in mind that the possible space groups require an evennumber of formula units in the unit cell, we are proposingthat Z = 6 leading to a calculated density of 4.95. A second
approach to the estimation of the unit cell contents was madeusing the average value of 20 A 3 for the volume occupied byoxygen atoms in other copper arsenates of known structure.
The unit cell volume is lO02 A 3, so we get about 50 oxygen
atoms, and the nearest multiple of 8 to this (there are eightoxygen atoms in two As04 groups) is 48, once again suggestingthat Z = 6.
Crystal morphology
Keyite crystals are as large as 0.25 x 0.1 x 0.04 mrn, but areusually much smaller, and it may be seen from the scanningelectron microscope(SEM) photographs(Fig. 2-5) that thelarger 'crystals' are aggregates of tablets in sub-parallel position ..We had no success in trying to measure crystals with theoptical goniometer.
but comparisonof calculated angles with
the SEM photographs shows the dominant forms to be b {OlO},m{IlO}, h{2lO}, q{Ol1}, and perhaps {20l} (seen only on thelargest, tapering crystal in Figure 2). An idealized crystal isdrawn in Figure 1. Under the microscope separated tablets lie
flat on {OlO}, and give a measured value of f3 98°50'. Thereis a good {OOI}cleavage. No twinning has been observed, reentrant angles being caused by thesub-parallel
growth. Calculated interfacial
angles are (110):(110) 84.45°; (011):(011)
56.31blue) > f3 (greenish blue) > a (pale blue). The optic axial
plane is {OlO}. Refractive indices for sodium light are a 1.80,
f3 not determined,
r 1.87. There is strong dispersion of theindicatrix , and crystals lying on {OlO}show purple and greenish
extinctions in white light. Extinction angles a:[001j, all in theacute angle f3, are lO1/2° (Cd red), 111/2° (Hg yellow), 121/2°(Hg green), and back to 91/2° (Hg violet). Interference
figures
showing the optic axes and their dispersions have not been
observed, and 2V and the optic sign have not be determined.

Physical properties
Keyite appears to scratch adamite, but not fluorite, so H
3112 - 4. The color is deep sky-blue, and the streak is pale blue;on hand specimen, green light reflected from the associatedcuproadamite
tends to mask the color of keyite. There is nofluorescence in U.V. radiation.

Name and type specimens
Keyite was approved by the I.M.A. Commission
on NewMinerals and Mineral Names in March 1975. The name is forCharles L. Key, mineral dealer of Canton, Connecticut.
whohas supplied the Museum with many fine and rare specimens
over the last few years. Holotype specimens, BM 1973,236 andBM 1975,660, are in the mineral collection,British Museum(Natural History).

0.

Optical properties
Keyite is strongly

pleochroicin shadesof blue:r (deepDiscussion
The superficial resemblance
between keyite and stranskiite
is striking, and it is unfortunatethat we have not been able toobtain any of the latter for study. Apart from the cadmium andthe Cu:Zn ratio, the simple formulae and the refractive indices
are much the same. The crystal symmetry, however, is entirely
different and there is no integral ratio between the unit cellvolumes. The higher symmetry of keyite, and the non-integral
numbers of the cations in the unit cell, taken in conjunction
with a larger oxygen volume (20.9 A3) than for stranskiite (19.1
A 3), lead us to speculate that keyite may be a disordered polymorph of stransk iite, possibly stabilized
by the cadmium.
Sidney Williams has recently sent us for comparison a powder
photographof a fragment of the type specimen of stransk iite,given to him by the Tsumeb Corporation.
The strongest lines
are 3.131 (lO), 2.789 (5), and 2.505 (5); neither they nor thepattern as a whole show any resemblance
to those of keyite.
Weare working to complete our description of the morphology
and optical properties of keyite.

89

Figure 5. Keyite: composite crystal lying on and in a 'cuproadamite' crystal. SEM, 500x

Figure 4. Keyite: composite crystal showing typical roughness offaces. SEM, 500x

Acknowledgements
We thank our friends Pierre Bariand, Prosper Williams,
Luis Teixeira-Leite, and Charles Key for the generous loan ofspecimens for microprobe examination, Sidney Williams forthe loan of his powder photograph of stranskiite, and Henry
Buckley for the SEM photographs.

Reference
STRUNZ, H. (1960). Stranskiit, ein neues Mineral. Naturwiss.
47, 376 [Abstracts in A mer. Mineral. 45, 1315; Mineral.
Abstr. 15, 213]. See also structure determination by K.
Plieth and G. Sanger, Zeits. Krist. 124, 91-100 [Mineral.
Abstr. 19,271]

Table 2. Keyite: X-ray powder data
(Cu-Ke, camera dia. 114.6 mm)
dobs

lobs

hkl

dobs

lobs

6.41
5.97
4.46
4.27
4.15

ms
vvw
vw
vvw
w

020,101011
21I, 121
220
121

2.515
2.386
2.320
2.266
2.230

mwSw
mw-mB
vw
w

3.R9
3.69
3.59
3.40
3.29

vw
mw
vw
w
vs(2)

211
310
30T,031
002
112

2.160

vvw

2.131
2.080
2.036w
vw
w-mw

3.15

m

231. 202, 301,
321

3.02
2.978
2.876
2.795
2.740
2.638

vw
vw
vs(3)
vvs(l)
mwwB

112
022
400
222, 321, 240141132, 420

Unit cell dimensions:

1.990
1.980
1.911
1.868
1.805
1.760w
vw
vvwB
vwB
vvw
mw

033, 323
260, 521, 213

dobs

lobs

1.718
1.700
1.644
1.602
1.566

w
mms
vwB
mwB

1.534
1.529
1.498
1.485
1.456w
vw
vw
vw
w

1.437

vw

1.413
1.406
1.384
1.379
1.346w
w
mw
vvw
vwBBa 11.65 A (± O.Old' b 12.68 (± 0.01), c 6.87 (± 0.01), ~ 98.95°(±0.05), V 1002.5A3.
Space group 12, Im, or 121m. Z = 6[(Cu,Zn,Cdls(As04hJ.

90hkl
222. 1:12
402, 341
312, 042, 332
510
25T, 422, 2·f2:.
341, 013
431, 103, 521,251440
501402. 123, 512,152

Dobs > 4.2, D calc 4.95.