149

Schultenite, a new mineral, from South-West Africcu]~y L. J. SI,~cE~, ~I.A., Sc.D., F.R.S.
With a chemicM analysis by E. D. ~[otr~*~Axx, ~I.A.
Mineral Department, British Museum (Natural tIistory).
[Road November 2, 1926.]

ARON A. DE SCHULTEN, x a political refugee from Finland, worked
during the latter part of his life in the chemical laboratories ofthe Sorbonne in Paris. There he prepared in a crystallized formnuml)er of minerals and compounds analogous to them. These weredetermined crystallographlcally and compared in isonlorphous series.
For example, having obtained crystals of artificial monetite, ~"C a t I P Q ,he then proceeded to prepare the corresponding compounds in whichstrontium, barimn, or lead take the place of calcium, and arsenic theplace of phosphorus, s In this series he determined the crystallographic
constants and optical data for CaHPO4, SrHPOI, B a K P Q , 1)bHPO4,SrHAsO4, and I)bHAsO~. Crystals of CaHAsO 4 were also obtained,
but they were too small tbr measurement. Any of these compounds
might be expected to occur in nature, but hitherto only monetite has
been found as a mineral. His 'mongtite ars~ni~e de plomb' is the,subject of the present note, and for ig, as a mineral, the name schultenite
is suggested. :Baron Schulten presented to the British Musemn collectionin 1898 a small set of his artificial products, but unfortunately theseinclude none of his monetite series.

B

1 August Benjamin Friherro af Schuit6n (1856-1912) ; obituary notice, Min.
]~Iag., 1913, vol. 16, p. 381.
A. de Schulten, Reproductioll artifieielle de la mon6tite. Bull. See. Frang.
~lin., 1901, vol. 24, pp. 323 326.
- - - - llecherches sur le phosphate dicalcique. Reproduction artificielle de l't
brushite. Reproduction de la mon(idte par un nouveau procdd6. Ibid., 1903,
vol. 26, pp. 11-17.
a A. de Schulten, Reproduction artifieiolle de mondtites de baryum, de plomb
et de strontium et do monStites ars6nidcs de plomb et de strontium. Ibid.,190~, vol. 27~ pp. 109-123. (hIoadtite arsdui.de de plomb, p. 113.)
L2

150I,. J. SPENCER ON

TMs compound, lead hydrogen orthoarsenate, P b H A s Q , is the ' l e a darsenate' of commerce, and was first prepared by J. J. ]3erzelius in1819. I t is used as an insecticide, especially in America in sprays forfruit-trees; and being practically insoluble in water it is no doubt
responsible for the retention of arsenic in apples. H. Goguel 1 in 1895
obtained monoc]inic crystals on which he determined some of thecharacters under the microscope. L a t e r , in 1916, C. C. McDonnell andC. M. Smith, 2 in a detailed study of the several forms of lead arsenate,also gave some of the microscopic characters.
As yet only a single specimen representing the new mineral is known.
but doubtless there are others in collections amongst the rich series ofcrystallized material that has come from the locality. This specimen[B.M. 1926, 205] was acquired in 1926 for the British Museum collection
from ~[r. Wilhelm Muncher of Munich, and was labelled ' Lanarkite :Tsumeb, Otavi, South-West A f r i c a ' . Although the mineral was incorrectly labelled lanarkite, there can be no doubt about the locality, forthe specimen is very typical of the pseudomorphous crusts that have beenfound in abundance at Tsumeb. The lead chloro-arsenate (mimetite) iscommon at this locality.
The specimen shows a base of large (2 cm. across) crystals of yellowish
anglesite which are altered on the surface and along cracks to bayldonite.
l~esting on the anglesite were tabular crystals probably of chessylite,
and hexagonal prisms and rods no doubt representing mimetite ; bothof these are now completely changed to bayldonite. The bayldonite(a basic arsenate of lead and copper) is yellowish-green in the interior,and bluish-green and minutely crystalline on the surface. The newmineral rests on these pseudomorphs, and is somewhat intermixed withbayldonite.
The schultenite has the form of thin crystal plates which are perfectlytransparent, clear, and colourless, and with a brilliant vitreous to almost
adamantine lustre. The largest plates measure 1 cm. across with athickness of 1 mm., and the smallest is about 1 ram. across. The
material is brittle and easily crushed to a white powder; hardness 289
The crystals are monoclinic (holohedra]) with the elements :a : b : c ----0.8643 : 1 : 0.7181, fi = 84 ~ 36",
1 It. Goguel~ C o n t r i b u t i o n ~ l'~tude des ars6niates e~ des a n t i m o n i a t e scristallis~s pr6par6s p a r voie h u m i d e . Mdm. Soc. Sci. Bordeaux~ 1895~ vol. 1~
pp. 83-157. (Orthoars6niate diplombique~ p. 135.)
C. C. McDonnell a n d C. 1~. S m i t h , J o u r n . A m e r . Chem. Soc.~ 1916~ vol. 38~
p. 2030. A s u m m a r y of t h e chemical literature is t h e r e given.

SCHULTENITE,A INIgW ]~IINERAL, I~ROM S O U T H - W E S T

AFIqICA.

I~I

as calculated from the measured angles co, el, and bl given in thefollowing table. A few other measured angles are also added for comparison with the calculated angles, sufficient to show that good results
were obtained.
~ean.
Limibs.
aNo. Calculated.
cp = (001) :(lU)... 4 5 ~45~1769*
cl = ( 0 0 1 ) : ( 1 3 0 )bl = ( 0 1 0 ) : ( 1 3 0 )bp = (010) : ( 1 1 1 )ce = ( 0 0 1 ) : ( 0 1 1 )st--(ff11):(221)

...
...
...
....
...

88
821 10~6 2 1235 36
16 33

88
2--88
218--2162
3--62
35 3 2 - - 3 5
16 3 0 - - 1 6

6
13
23
40
38

6816
68

*
*
62 ~ 16'3 5 31
16 3 2The complete list of sixteen forms and ~heir angles is, however, given
in a form of table (•. i58), which, it is beI{eved, combines tim advantages
both of the arrangement in zones of interracial angles (as adopted by Miller,Dana, ttintze, and Groth) and of the ~ and p (longitude and latitude)
angles employed in two-circle goniometry (as advocated by Goldsehmidt). For monoclinic crystals the polar distances p are moreconveniently taken from the fixed b-axis (the axis of symmetry), rather
than from the arbitrary c-axis as done by Goldschmidt. The angle
between any two faces lying in a zone containing one of the axial planes
is at once given by the difference between two angles in the table.
Such a table of angles can be quickly checked by placing a transparent
stereographic net over tile projection (fig. 3).
The crystals are all flattened parallel to the plane of symmetry b (010),parallel to which there is a good cleavage. The usual habit is rhombshaped (fig. 1), with much the appearance of crystals of gypsum. Asmall (1 ram.) crystal of this type, which was mounted on the goniometer, is completely developed on all sides. Less often the pyramidfaces 2 4111) are partly or sometimes completely cut out by the basal
plane c (001) (fig. 2). The prolninent prism is /(130), and n ( 1 4 0 ) i s
usually present as narrow faces, but m (110) is only rarely represented.
Small clino-dome faces e t011) sometimes border the basal plane when
the latter is present. Except for 2(111), all the pyramid-faces arequite small. The faces b (010) are prominently striated parallel totheir intersection with the prism-faces; and when c(001) is present
they also bear less prominent striations parallel to and close to theedge b/s. The prism-faces are faintly striated vertically. The basal
p l a n e and the pyramids are perfectly smooth, and give single sharp
images when not confused b y sub-parallel growth of the crystals.
The determination of the optical constants presented some difficulty
and unfortunately is not complete. The crystals are very thin andbrittle, and the thicker and better crystals on the single specimen

152

L . J . SPENCER ON

could not be sacrificed for cutting oriented plates and prisms. Measurements of the extinction-angle on the plane of symmetry gave readings
varying from 19 ~ to 28 ~ to the prism-edge in the acute angle fi, themean being 24 ~. Owing to the high refraction, the optic axes do not
emerge into air through b(010), and it was consequently at firstthought that the optic axial plane was parallel to the plane ofsymmetry (as previously described for the artiticial crystals): One
optic axis is, however, visible through /)(111). A small fragment
broken approximately perpendicular to the plane of symmetry and thecleavage, and giving straight extinction, showed a wide-angle biaxial
figure of positive sign with the optic axial plane perl~endicular to theplane of symmetry. The angle was estimated under the microscopewith a micrometer scale as 2Ea = 185 ~ By immersing a crystal ina trough of methylene iodide it was possible to observe the obtuse
angle through b (010), and on the Fuess axial angle apparatus this wasmeasured as 2go ---- 14:6~ 84/ for sodium-light. Taking fl as 1"9097
and for methylene iodide n = 1.742, this gives :2V~ ----58 ~ 14:' and 2E~ = 186 ~ 88' (Na).
The optical orientation of the crystals is: optic axial plane perpendicular to the plane of symmetry and lying in the obtuse angle fi ;a(Bxo)'= b, fi:c = --24 ~, 7(Bx~):c = + 6 6 ~sign positive. These
directions are plotted on the stere0graphic projection (fig. 8).
Refractive indices were determined by the prism method of minhnnm
deviation through the natural prism given by the faces /(130)(130),the refracting angle on the crystal employed being measured as 42 ~ 22 t.
In such a prism the path of the light is symmetrical through the prismin the direction of the axis of symmetry ; and the vibration-directions
fi and ~/ lie in the plane o f symmetry, though not parallel and perpendicular to the refracting edge of the prism. The use of naturalprisms of orthorhombic crystals in this connexion is well recognized,
when the vibration-directions are p~rallcl and perpendicular to therefracting edge; but for monoclinic crystals I have not been able tofind any mention of this method in the text-books on crystallography
and crystal-optics. With white light the schultenite prism gave twolong and widely separated spectra, indicating high dispersion and strong
birefringence. The crystal used was small and readings could not be
obtained for lithium- and thallium-light. The values determined for
sodium-light are :fl = 1"9097 and 7 = 1"9765 (Na).
Calculated from fl, 7, and 2V, the value of a is 1"8903.

SCIIULTENIT:E~ A .NEW MINEI~AL~ ]:'1~.05[ SOUTH~WEST AFRICA.

153

hob,~oloD.

lF~(4. 1.

'~140"-.

~2~\I/
2 i o.~

713oFI~. 3.

Fro. 2.

C r y s t a l s a n d S t e r e o g r a l ) h i c P r o j e c t i o n of S c h u l ~ e n i t e .

Forms of Schultenite aqul the normal angles of each to the three
axial planes.
A n g l e to..,,.._~orm~.
b(010)c(001)--......
......

h,~lO)

m(llO)......
I k(120)......
,
1 (130)......
_ ~ (140)......
e (011) . . . . . .
labs.(101)] ......
~_,.tbs. (1_02)~ . . . . . .
[~bs. (101)] . . . . . .
'Labs. (~01)] . . . . . .
~-- w ' 3 2 3 ) . . . . . .
i ,v(111) . . . . . .
I v(~......
_ ~(121)......
i-- r ( 1 2 2 "......
q~:lll)i s(:)ll)......
(221) . . . . . .

...

~00)

~ <01,)).

c (001~.

90 ~ 0'84 36
23 1740 43
5 9 .,068 50
73 4 885 86474107 55
126 33147 3750 052 55
57 40
620104 -~3]'21 3]421132
1-90 ~ 0'
66 43
49 17
30 l 021 1016 12
54 26
90 090 09,) 0
90 0
70 41
61 16
51 444") 34
55 39
60
168 5852 26

90 ~ 0 '-85 286 087 17
88388 3035 "~4:37 32
23 1941 57
63
141 3245 2551 2956 5 240 42
4 9 5464 57
68 56

The question of the crystallographic orientation must now be considered, since the one here adopted differs from that of Schulten for theartificial crystals, t i e gave the elements as a : b 9 c = 0.7212 : 1 : 0"8704,
fl = 84 ~ 23', and the forms recorded by him were gl(010), m ( l l 0 ) ,154

L. Z. S~ENCXR ON

e1 (011), b89( i l l ) , and b1 (i12).
Groth ~ adopts Schulten's orientation
but letters the forms b m q o ~ i respectively. The difference amountsonly to an interchange of the a and c axes ; but to get the crystals into
parallel position one must be rotated through 8489~ and then turned
over (180 ~ about the new c-axis~ The first and last indices of theforms must also be interchanged, but this affects only some of the forms.
The following tabular comparison shows the differences, and at thesame time shows that Schulten's measured angles (except those on
which the calculations are based) are in closer agreement with myvalues than with his own calculated values.
Sehulten.
Angle.
Obs.
(0105 : (11055d~~ 20'(011) : (1105
63 46(011) : (i10)71 15(010):(011)
49 13(010) :(i11)
60 1(010) : (i12)~8 55(1105:(i11)
85 17(i12) :(i11)
20 59

Calc.
*
*
*

19~ C'
59 50
68 48
85 20
21 0

Spencer.
Angle.
Calc.
(010) : (011)
54~ 26'(110): (0115
64 4(]10) :(011)
71 16(010):(110)49 17(010) : ( i l l )60 1(010) : (211)68 58(011) :(i11)35 27(211): (]11)
20 58

On the natural crystals now described the zone chosen by Schulten
for the prism-zone is frequently not developed (fig. 1), and when it ispresent [b e cj the prism-faces e are always small. Further, it is to be
noted that the orientation here adopted is the same as the earlier one
shown in the figure of H. Goguel (1895), whose paper is not mentioned
by Schulten and was apparently unknown to him.
There remains the question of the optical orientation, which has been
given incorrectly by previous authors for the artificial crystals. Gogueland Schulten both state that the optic axial plane is parallel to theplane of symmetry (this has been dealt with above). Goguel measured
under the microscope the angle fi as 83 ~ 24', and McDonnell and Smith(1916) give the corresponding value 84~ but both these authors givethe extinction as being in the obtuse (not acute) angle fl, their values tothe prism-edge being + 2 1 ~ to 22 ~ (for n~ [i.e. fl~) and + 2 9 ~ respectively. Schulten gives the extinction-angle as 38 ~ in the obtuse angle,
which in the second orientation is equivalent to 3289~ in the acute angle ft.
The statement of obtuse for acute angle is evidently a slip, and thevariation 21 ~ to 3289~ (compare 19 ~ to 28 ~ above) may perhaps be dueto dispersion.
1 p. Groth, Chem. Kryst.~ 1908, vol. 2, p. 822.

SCtIULTENITE~ A HEW 5II~EI~AL, FROM

SOUTH-WEST AFRICA.

155

I t may be mentioned that the data recorded above for the natural
crystals were all determined before the identity of the mineral with theartificial crystals was established by ~ r . Mountain's analysis.
The
substance could not be identified from the crystallographic data alone,since a copy of Fedorov's ' Tables for Crystallo-chemical A n a l y s i s ' was
not available.
PseudomorThs of anglesite after schultenite(?).--Another specimen[B.M. 1922, 388] from Tsun~eh, acquired from ~Ir. W. Maucher in 1922,
was labelled ' A n g l e s i t e pseudomorphous after a monoclinic mineral(lanarkite ? or gypsum ?) '. This shows lath-shaped tabular crystals up
to 189 cm. long which are completely changed to an aggregate of small
crystals of anglesite and stained with a later thin deposit of bayldonite.
Most of the pseudo-crystals are merely hollow Crusts, and, consisting ofan aggregate of anglesite crystals, the form is not always distinct.
Terminated crystals, however, show a form suggestive of fig. 1, and it
is possible that these are really pseudomorphs of anglesite after
schultenite.

Chemical Analysis of Sc7~ultenite.
The total weight of available material was 0.2981 gram. The crystal
fragments were collected by Dr. Spencer and contained only a minutetrace of bayldonite, the copper of which was not sufficient to determine.
A specific gravity1 determination by the pyknometer method gavea corrected value of 5.943.
The analysis was made on 0"2917 gram. The water was determined
as loss of weight on heating to incipient fusion. The residual powder
was dissolved in a small quantity of dilute nitric acid and the lead wasprecipitated as lead sulphate. Subsequently the arsenic w a s estimatedas sulphide after prolonged reduction by hydrogen sulphide. The
analysis gave the following results :l~Iolec, ratios.
Calculated.
PbO . . . . . .
63.97
...
0.287
2...
64.24
As20~ . . . . . .
~2.18 ...
0.140
1...
33.17
I420 . . . . . .
2.88...
0.160 1...
2.59
99.03

100.00This corresponds with the formula 2PbO. As205 . H20 or P b H A s Q .
i Specific gravity of the artificial crystals 6.076 (Schulten, 1904), 6.053(NcDonall and Smith, 1916).