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1457

The Canadian Mineralogist

Vol. 38, pp. 1457-1466 (2000)



ADAMSITE-(Y), A NEW SODIUM–YTTRIUM CARBONATE MINERAL SPECIES

FROM MONT SAINT-HILAIRE, QUEBEC

JOEL D. GRICE

§

 and ROBERT A. GAULT



Research Division, Canadian Museum of Nature, P.O. Box 3443, Station D, Ottawa, Ontario K1P 6P4, Canada

ANDREW C. ROBERTS



Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada

MARK A. COOPER



Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada

A

BSTRACT



Adamsite-(Y), ideally NaY(CO

3

)



2

•6H


2

O, is a newly identified mineral from the Poudrette quarry, Mont Saint-Hilaire, Quebec.

It occurs as groups of colorless to white and pale pink, rarely pale purple, flat, acicular to fibrous crystals. These crystals are up

to 2.5 cm in length and form spherical radiating aggregates. Associated minerals include aegirine, albite, analcime, ancylite-(Ce),

calcite, catapleiite, dawsonite, donnayite-(Y), elpidite, epididymite, eudialyte, eudidymite, fluorite, franconite, gaidonnayite,

galena, genthelvite, gmelinite, gonnardite, horváthite-(Y), kupletskite, leifite, microcline, molybdenite, narsarsukite, natrolite,

nenadkevichite, petersenite-(Ce), polylithionite, pyrochlore, quartz, rhodochrosite, rutile, sabinaite, sérandite, siderite, sphalerite,

thomasclarkite-(Y), zircon and an unidentified Na–REE carbonate (UK 91). The transparent to translucent mineral has a vitreous

to pearly luster and a white streak. It is soft (Mohs hardness 3) and brittle with perfect {001} and good {100} and {010} cleav-

ages. Adamsite-(Y) is biaxial positive, 

␣ = 1.480(4), ␤ = 1.498(2), ␥ = 1.571(4), 2V

meas.


 = 53(3)

°

, 2V



calc.

 = 55


°

 and is nonpleochroic.

Optical orientation: X = [001], Y = bZ 

 a = 14

°

 (in 


␤ obtuse). It is triclinic, space group P¯1, with unit-cell parameters refined

from powder data: a 6.262(2), b 13.047(6), c 13.220(5) Å, 

␣ 91.17(4), ␤ 103.70(4), ␥ 89.99(4)

°

V 1049.1(5) Å



3

 and Z = 4. The

strongest six X-ray powder-diffraction lines [d in Å(I)(hkl)] are: 12.81(100)(001), 6.45(70)(002), 4.456(60)(¯1¯21,¯120),

4.291(60)(003), 2.571(60)(005, 043) and 2.050(50)(125,¯126). Electron-microprobe and thermogravimetric analyses, supported

by crystal-structure analysis and infrared-absorption spectroscopy, yield Na

2

O 8.64, CaO 0.05, Y



2

O

3



 22.88, Ce

2

O



3

 0.37, Nd

2

O

3



1.41, Sm

2

O



3

 1.02, Gd

2

O

3



 1.92, Tb

2

O



3

 0.56, Dy

2

O

3



 3.28, Ho

2

O



3

 0.90, Er

2

O

3



 2.83, Tm

2

O



3

 0.27, Yb

2

O

3



 1.04, CO

2

 25.10, H



2

O

29.90, total 100.17 wt.%. The empirical formula, based on 12 oxygen atoms, is Na



1.00

 (Y


0.72

Dy

0.06



Er

0.05


Gd

0.04


Nd

0.03


Yb

0.02


Sm

0.02


Ho

0.02


Ce

0.01


Tb

0.01


Tm

0.01


)

⌺0.99


 C

2.04


H

11.87


O

12

. The calculated density (from the empirical formula) is 2.27 g/cm



3

, and the meas-

ured density is 2.27(2) g/cm

3

. The structure has been refined to R = 0.046. The structure is layered, with two different carbonate



groups, one parallel and one perpendicular to the layering. Slabs of [NaY(CO

3

)] are separated by [H



2

O] layers. Adjacent [H

2

O]

layers are only H-bonded together, which gives rise to the perfect {001} cleavage. The mineral is named after Frank Dawson



Adams (1859–1942), geologist and professor at McGill University, Montreal.

Keywords: adamsite-(Y), new mineral species, sodium yttrium dicarbonate hexahydrate, crystal structure, Mont Saint-Hilaire,

Quebec.


S

OMMAIRE


La nouvelle espèce minérale adamsite-(Y), de composition idéale NaY(CO

3

)



2

•6H


2

O, a été découverte à la carrière Poudrette,

au mont Saint-Hilaire, Québec. Elle se présente en groupes de cristaux incolores, blancs ou rose pâle, et plus rarement violacés,

plats et aciculaires ou fibreux. Ces cristaux atteignent 2.5 cm en longueur et forment des agrégats fibroradiés. Lui sont associés

aegyrine, albite, analcime, ancylite-(Ce), calcite, catapleiite, dawsonite, donnayite-(Y), elpidite, epididymite, eudialyte,

eudidymite, fluorite, franconite, gaidonnayite, galène, genthelvite, gmelinite, gonnardite, horváthite-(Y), kupletskite, leifite,

microcline, molybdénite, narsarsukite, natrolite, nenadkevichite, petersenite-(Ce), polylithionite, pyrochlore, quartz,

rhodochrosite, rutile, sabinaïte, sérandite, sidérite, sphalérite, thomasclarkite-(Y), zircon et un carbonate à Na–REE non encore

identifié (UK 91). Le minéral est transparent à translucide et possède un éclat vitreux à nacré et une rayure blanche. Il s’agit d’un

minéral mou (dureté de Mohs de 3) et cassant, ayant un clivage {001} parfait et des clivages {100} et {010} assez bons.

§

E-mail address: jgrice@mus-nature.ca

V

1457 38#6-déc.00-2203-13



27/02/01, 13:29

1457


1458

THE


 

CANADIAN


 

MINERALOGIST

I

NTRODUCTION



The new mineral species described herein, adamsite-

(Y), is the latest in a series of new carbonate minerals

recently described from the Poudrette quarry, Mont

Saint-Hilaire, Rouville County, Quebec. Fifty-seven

carbonate species are known to occur at Mont Saint-

Hilaire, many of them containing essential Na and rare-

earth elements (REE) (Grice & Gault 1998). To date, a

total of 333 mineral species have been identified from

this locality, a well-known source of rare and exotic

minerals (Horváth & Gault 1990).

Adamsite-(Y) was initially recognized as being a

new species in 1992 by Dr. G.Y. Chao, Carleton Uni-

versity, on material submitted by a private collector,

Gilles Haineault, and was designated as UK 96. In 1998,

more material was found, but the chemical and X-ray

data were not compared with those of the initial find,

and the mineral from this second find was designated

UK 106. It has since been determined that these two

minerals are identical. Another mineral with similar

chemical composition, similar appearance, and found in

the same environment as adamsite-(Y), has been desig-

nated as UK 91. This material is more finely fibrous

than adamsite-(Y), however, and has a significantly dif-

ferent X-ray powder-diffraction pattern.

Adamsite-(Y) is named in honor of Frank Dawson

Adams (1859–1942), geologist and professor at McGill

University, Montreal. After graduating in chemistry and

mineralogy from McGill University, he joined the Geo-

logical Survey of Canada in 1879 as “lithologist” and

chemist. He studied the new science of petrography at

Heidelberg, Germany in 1881 and went on to become

the Survey’s leading specialist in the study of crystal-

line rocks. In 1889, he was appointed Logan Professor

of Geology at McGill University, where he continued

his studies on Precambrian rocks, particularly those of

the Laurentian and Grenville regions of Quebec and

Ontario. It was during this period that he studied the

Cretaceous igneous rocks of the Monteregian Hills, of

which Mont Saint-Hilaire is a member, and was the first

to describe this group of hills as the Monteregian Hills

petrographic province (Adams 1903). As well, he served

as president of the Geological Society of America and

the Canadian Mining Institute.

The new mineral and mineral name were approved

by the Commission on New Minerals and Mineral

Names, IMA. Cotype material is housed in the collec-

tion of the Canadian Museum of Nature under catalogue

numbers CMNMC 82939 and CMNMC 82940.

O

CCURRENCE



Adamsite-(Y) occurs as a late-stage, low-tempera-

ture hydrothermal phase within cavities in a large alka-

line pegmatite dike, informally designated the Poudrette

dike, exposed in the southern corner of the Poudrette

quarry. The quarry, in turn, is situated on the northeast-

ern flank of Mont Saint-Hilaire, one of a series of plu-

tons aligned along the St. Lawrence Valley for almost

150 km eastward from Oka to Megantic, in the prov-

ince of Quebec. The pegmatite dike, which pinches and

swells from 2 to 4 m across, has been exposed on levels

6, 7, 8 and 9 of the quarry. Five new Na- and REE-bear-

ing carbonate mineral species have been described from

this dike: lukechangite-(Ce), horváthite-(Y), reederite-

(Y), thomasclarkite-(Y) and adamsite-(Y), the subject

of this paper. Minerals found in that portion of the dike

in which adamsite-(Y) was discovered include aegirine,

albite, analcime, ancylite-(Ce), calcite, catapleiite, daw-

sonite, donnayite-(Y), elpidite, epididymite, eudialyte,

eudidymite, fluorite, franconite, gaidonnayite, galena,

genthelvite, gmelinite, gonnardite, horváthite-(Y),

kupletskite, leifite, microcline, molybdenite, narsarsuk-

L’adamsite-(Y) est biaxe positive

␣ = 1.480(4), ␤ = 1.498(2), ␥ = 1.571(4), 2V

mes.


 = 53(3)

°

, 2V



calc.

 = 55


°

, et non pléochroïque.

Son orientation optique est: X = [001], Y = bZ 

 a = 14

°

 (dans l’angle 



␤ obtus). Le minéral est triclinique, groupe spatial P¯1,

avec une maille élémentaire affinée à partir des données obtenues sur poudre: a 6.262(2), b 13.047(6), c 13.220(5) Å, 

␣ 91.17(4),

␤ 103.70(4), ␥ 89.99(4)

°

V 1049.1(5) Å



3

 et Z = 4. Les six raies les plus intenses du spectre de diffraction X [d en Å(I)(hkl)] sont:

12.81(100)(001), 6.45(70)(002), 4.456(60)(¯1¯21,¯120), 4.291(60)(003), 2.571(60)(005, 043) et 2.050(50)(125, ¯126). Les analyses

obtenues par microsonde électronique et par thermogravimétrie, supplémentées par une ébauche de la structure cristalline et un

spectre d’absorption dans l’infra-rouge, mène à la composition Na

2

O 8.64, CaO 0.05, Y



2

O

3



 22.88, Ce

2

O



3

 0.37, Nd

2

O

3



 1.41,

Sm

2



O

3

 1.02, Gd



2

O

3



 1.92, Tb

2

O



3

 0.56, Dy

2

O

3



 3.28, Ho

2

O



3

 0.90, Er

2

O

3



 2.83, Tm

2

O



3

 0.27, Yb

2

O

3



 1.04, CO

2

 25.10, H



2

O 29.90,


pour un total de 100.17% (poids). La formule empirique, fondée sur une base de 12 atomes d’oxygène, est Na

1.00


 (Y

0.72


Dy

0.06


Er

0.05


Gd

0.04


Nd

0.03


Yb

0.02


Sm

0.02


Ho

0.02


Ce

0.01


Tb

0.01


Tm

0.01


)

⌺0.99


 C

2.04


H

11.87


O

12

. La densité calculée (à partir de la formule empirique) est



2.27 g/cm

3

, et la densité mesurée est 2.27(2) g/cm



3

. La structure a été affinée jusqu’à un résidu R de 0.046. L’adamsite-(Y) est un

minéral en couches ayant deux groupes de carbonate distincts, un parallèle aux couches et l’autre perpendiculaire. Les couches de

composition [NaY(CO

3

)] sont séparées par des couches de [H



2

O]. Les couches adjacentes de [H

2

O] ne sont interliées que par



liaisons hydrogènes, ce qui rend compte du clivage {001} parfait. Le minéral honore Frank Dawson Adams (1859–1942), géologue

et professeur à l’Université McGill.

(Traduit par la Rédaction)

Mots-clés: adamsite-(Y), nouvelle espèce minérale, bicarbonate de sodium et yttrium hexahydraté, structure cristalline, mont

Saint-Hilaire, Québec.

V

1457 38#6-déc.00-2203-13



27/02/01, 13:29

1458


ADAMSITE

-(

Y



FROM


 

MONT


 

SAINT


-

HILAIRE


QUEBEC


1459

F

IG



. 1.

Photograph of adamsite-(Y). Photograph by Harry Taylor. The National History Museum, London, specimen number

BM 1998, 172. Scale bar: 1 cm.

1457 38#6-déc.00-2203-13

27/02/01, 13:29

1459


1460

THE


 

CANADIAN


 

MINERALOGIST

ite, natrolite, nenadkevichite, petersenite-(Ce), poly-

lithionite, pyrochlore, quartz, rhodochrosite, rutile,

sabinaite, sérandite, siderite, sphalerite, thomasclarkite–

(Y), zircon and an unidentified Na–REE–carbonate (UK

91). We discuss the genesis of adamsite-(Y) later in this

paper.


P

HYSICAL


 

AND


 O

PTICAL


 P

ROPERTIES

Adamsite-(Y) occurs as flat, acicular to fibrous crys-

tals, up to 2.5 cm in length. They typically form spheri-

cal groups of radiating crystals, and rarely form

reticulated groups (Fig. 1). The mineral is elongate on

[001] and flat on (001). Forms observed are the

pinacoids {010} and {001}. It is colorless to white, oc-

casionally pale pink, and rarely pale purple. It is trans-

parent to translucent with a vitreous and occasionally

pearly luster, and a white streak. It is brittle with perfect

{001} and good {100} and {010} cleavages. Adamsite-

(Y) is relatively soft (Mohs hardness 3) and does not

fluoresce in either long- or short-wave ultraviolet light.

The density, measured by suspension in a solution of

bromoform and butyl alcohol, is 2.27(2) g/cm

3

, which


compares very well to the density of 2.27 g/cm

3

 calcu-



lated for the empirical formula.

Adamsite-(Y) is biaxial positive, 

␣ 1.480(4), ␤

1.498(2), 

␥ 1.571(4); 2V

meas.


 = 53(3)

°

, 2V



calc.

 = 55


°

, (for


␭ = 590 nm). The optical orientation is X = [001], Y = b,

Z 

  a = 14

°

 (in 


␤ obtuse). It is nonpleochroic. A

Gladstone–Dale calculation gives a compatibility index

of –0.009, which is regarded as superior (Mandarino

1981).


C

HEMICAL


 C

OMPOSITION

Chemical analyses were done in wavelength-disper-

sion (WD) mode on a JEOL 733 electron microprobe

using Tracor Northern 5500 and 5600 automation. Data

reduction was done with a PAP routine in XMAQNT

(pers. commun., C. Davidson, CSIRO). The analysis of

adamsite-(Y) by electron microprobe was problematic

because of decrepitation of the sample and the lifting of

the carbon coating due to dehydration under prolonged

vacuum. The decrepitation results from the weak H-

bonding linking adjacent H

2

O groups in the structure.



To minimize this effect, calibration of the standards was

performed first, and the samples were later introduced

into the specimen chamber and analyzed immediately.

This method, along with adoption of a rather large di-

ameter of the beam, 50 

␮m, limited Na migration, vola-

tilization and general burn-up of the sample. The

operating voltage of the electron probe was 15 kV, and

the beam current was 20 nA. Data for all elements in

the samples were collected for 25 s or 0.50% precision,

whichever was attained first. A 100 s energy-dispersion

scan indicated no elements with Z > 8 other than those

reported here. Seven analyses were performed on three

crystals. The presence of CO

2

 and H


2

O was confirmed

by infrared-absorption spectroscopy, and their concen-

trations were established by thermogravimetric analy-

sis (TGA). As only one-half of the CO

2

 was evolved



during TGA, the amount given below consists of two

summed portions, one measured (the gas evolved, 12.9

wt.%) and the other, the ideal amount determined by

crystal-structure analysis (non-evolved during heating,

12.2 wt.%).

The following standards were used in the electron-

microprobe analyses: albite (NaK

␣), calcite (CaK␣),

synthetic yttrium iron garnet (YIG) (YK

␣), and a set of

synthetic REE phosphates (CeL

␣, NdL␣, SmL␣, GdL␣,

TbL

␣, DyL␤, HoL␣, ErL␣, TmL␣, YbL␣). La, Pr and

Eu were sought but not detected. Lu was detected in

trace amounts. Data for standards were collected for 50

s or 0.25% precision, whichever was attained first. The

REE raw data were corrected for overlaps. The chemi-

cal composition is Na

2

O 8.64, CaO 0.05, Y



2

O

3



 22.88,

Ce

2



O

3

 0.37, Nd



2

O

3



 1.41, Sm

2

O



3

 1.02, Gd

2

O

3



 1.92,

Tb

2



O

3

 0.56, Dy



2

O

3



 3.28, Ho

2

O



3

 0.90, Er

2

O

3



 2.83,

Tm

2



O

3

 0.27, Yb



2

O

3



 1.04, CO

2

 25.10, H



2

O 29.90, total

100.17 wt.%. The empirical formula, based on 12 at-

oms of oxygen, is Na

1.00

(Y

0.72



Dy

0.06


Er

0.05


Gd

0.04


Nd

0.03


Yb

0.02


Sm

0.02


Ho

0.02


Ce

0.01


Tb

0.01


Tm

0.01


)

⌺0.99


C

2.04


H

11.87


O

12

.



This simplifies to the ideal formula NaY(CO

3

)



2

•6H


2

O.

Adamsite-(Y) readily dissolves with strong efferves-



cence in 10% HCl and decrepitates owing to dehydra-

tion in acetone (rapid) and alcohol (slow).

T

HERMOGRAVIMETRIC



 

AND


 D

IFFERENTIAL

T

HERMAL


 A

NALYSIS


Two differential thermogravimetric analyses (DTG)

of adamsite-(Y) were done using a Mettler–Toledo

TA8000 system (software version 3.0), which uses a

Mettler TG50 module linked to a Mettler M3 microbal-

ance. The purge gas was dry nitrogen, with a flow rate

of 200 mL/min. Two samples of pure material, weigh-

ing 10.196 and 10.847 mg, respectively, were each

ground to a fine powder and heated from room tempera-

ture to 1000

°

C at a rate of 5



°

C/min. The weight losses

of 4.334 mg (42.5 wt.%) and 4.670 mg (43.1 wt.%) oc-

curred in two major steps (DTG, Fig. 2): between 80

and 270

°

C, 27.0 wt.% on average and between 380 and



590

°

C, 15.8 wt.% on average. The interpretation of the



DTG scan is given in Table 1. The first weight-loss step

is interpreted as the loss of 10 (H

2

O) groups, which ide-



ally should be 25.0 wt.%, making the measured value a

V

1457 38#6-déc.00-2203-13



27/02/01, 13:29

1460


ADAMSITE

-(

Y



FROM


 

MONT


 

SAINT


-

HILAIRE


QUEBEC


1461

little high. The second weight-loss step is interpreted as

the loss of two additional (H

2

O) groups plus the break-



up of one of the (CO

3

)



2–

 anions and its loss as CO

2

(Mochizuki et al. 1974). Ideally, this second weight-loss



step should be 12.2 wt.%, making the observed value of

12.9 wt.% a little high. Mochizuki et al. (1974) dis-

cussed their DTG and differential thermal analysis

(DTA) results on synthetic double carbonates similar in

composition to adamsite-(Y). The TGA and DTA curves

they presented are very similar to those of adamsite-(Y).

They proposed that the final product after heating is a

REE oxycarbonate, e.g., YNaO(CO

3

). Although the



final product after heating was X-rayed, we found no

suitable match to any compound listed in the Powder

Diffraction File (PDF), including NaYO

2

 (PDF 32–



1203). It is well established that the production of so-

dium peroxide, Na

2

O

2



, takes place at temperatures

below 500

°

C (Cotton & Wilkinson 1980). Thus an al-



ternative explanation is that Na acts as a reducing agent

for the entire system and evolves CO, not CO

2

, and that



the final product is a peroxide, NaYO

4

. Although two



possible end-products of heating have been postulated,

there is a preference for the REE oxycarbonate based

on a chemical test with HCl that produced efferves-

cence.


The differential thermal analysis curve (DTA, Fig.

2) reveals one smooth endothermic peak for the initial

loss in H

2

O, followed by a distinct shoulder that corre-



sponds to almost 25% of the weight percent loss in H

2

O.



This weight loss would be the H

2

O groups more strongly



bonded to both Na and Y (OW13 and OW15; see be-

low), whereas the other H

2

O groups are bonded to Na



only (OW17, OW18, OW19, OW20, OW21, OW22,

OW23 and OW24). The second weight-loss is trimodal

on the DTA curve and is due to the difference in energy

required to drive off two additional H

2

O groups (OW14



and OW16) and the two less strongly bonded (CO

3

)



2–

groups.


F

IG

. 2.



Differential thermogravimetric analysis (DTG) and

differential thermal analysis (DTA) of adamsite-(Y).

F

IG

. 3.



Infrared-absorption spectrum of adamsite-(Y).

1457 38#6-déc.00-2203-13

27/02/01, 13:29

1461


1462

THE


 

CANADIAN


 

MINERALOGIST

I

NFRARED


 S

PECTROSCOPY

The infrared-absorption spectrum of adamsite-(Y)

(Fig. 3) was obtained using a Bomem Michelson MB–

120 Fourier-transform infrared spectrometer equipped

with a diamond-anvil cell as a microsampling device.

The dominant absorption band is that of the O–H

stretching mode (3297 cm

–1

). The (H



2

O) bending band

(1673 cm

–1

) forms a shoulder on the large, split, asym-



metric stretching band for (CO

3

)



2–

. This splitting (1513

and 1377 cm

–1

) is explained by the fact that the carbon-



ate groups are very distorted, with distinctly differing

C–O bond lengths, as seen in the crystal-structure de-

termination. For this same reason, the (CO

3

)



2–

 symmet-


ric band is also split (1115 and 1070 cm

–1

). The weak



intensity of this symmetric band is due to the limited

ability of the (CO

3

)

2–



 group to undergo this type of

stretching mode. The 876 and 849 cm

–1

 bands may be



due to out-of-plane bending of (CO

3

)



2–

. The remainder

of the spectra could not be unequivocally assigned. This

infrared-absorption spectrum is very similar in appear-

ance to that of thomasclarkite-(Y) (Grice & Gault 1998).

In thomasclarkite-(Y), the splitting of the carbonate

peaks is due to the presence of the (HCO

3

)



 anion,


whereas in adamsite-(Y), the splitting of the carbonate

peaks is due to the influence of H-bonding.

X-R

AY

 C



RYSTALLOGRAPHY

 

AND



C

RYSTAL


-S

TRUCTURE


 D

ETERMINATION

Precession single-crystal photographs initially

showed adamsite-(Y) to be pseudo-orthorhombic, with

diffraction symmetry mmm. These crystals are twinned

by reflection on {001}; subsequent more precise work

on single crystals using a four-circle diffractometer in-

dicated triclinic symmetry, but metrically close to mono-

clinic. Much of the problem with the early single-crystal

work was the failure to realize that this mineral reacts

with the binding agent, amyl acetate, causing dehydra-

tion and subsequent almost complete decrepitation of

the crystal. This decrepitation reaction was exacerbated

by intense X-radiation; crystals subjected to this treat-

ment developed a crazed appearance. The crystal used

for the final data-collection was mounted on a glass fiber

with non-reacting epoxy. X-ray powder-diffraction data,

obtained with a Debye–Scherrer camera having a diam-

eter of 114.6 mm and using CuK

␣ radiation, are given

in Table 2. Whereas neither variation in intensity nor

shifting of d-values was noted in the X-ray powder pat-

terns during this study, other researchers have noted

some variability in the patterns, possibly indicating that

adamsite-(Y) may not be stable under minor fluctuations

in humidity levels (pers. commun., A.M. McDonald,

Laurentian Univ.). Indexing the powder data was diffi-

cult owing to the previously mentioned pseudosym-

metry, but the process was successful with the aid of

powder-pattern intensities calculated from the results of

the crystal-structure analysis.

In the final stage of data collection, a crystal frag-

ment of adamsite-(Y), measuring 160

 ϫ 180 ϫ 40 ␮m

for [100]

 ϫ [010] ϫ [001], was mounted on a CCD-

equipped Bruker P4 fully automated four-circle

diffractometer operated at 40 kV and 40 mA. With the

CCD detector, almost a full sphere of intensity data was

collected out to 2

␪ = 60

°

 using a 15 s frame time and a



crystal-to-detector distance of 4 cm. The lowering of the

incident radiation power and the high-speed data col-

lection were in anticipation of potential problems with

crystal decrepitation. With these operating conditions,

1457 38#6-déc.00-2203-13

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1462


ADAMSITE

-(

Y



FROM


 

MONT


 

SAINT


-

HILAIRE


QUEBEC


1463

no decrepitation was evident in the final analysis of the

intensity standards. Information relevant to the data

collection and structure determination is given in

Table 3. The three-dimensional data were reduced for

Lorentz, polarization, and background effects using the

Bruker program SAINT. An empirical plate-absorption

correction was done on the basis of 3998 reflections and

reduced the merging R of this dataset from 3.45% be-

fore the absorption correction to 3.10% after the absorp-

tion correction with a glancing angle of 7

°

.



Phasing of a set of normalized structure-factors gave

a mean value | E

2

 – 1 | of 0.862. A calculated sharpened



Patterson function for space group P¯1 located the two Y

sites, the two Na sites and six lighter-element sites. This

model refined to R = 0.22. Additional O and C sites were

added following a series of 

F synthesis maps, which,

in turn, reduced the R index to 0.066. In the final least-

squares refinement, all atomic positions were refined

with anisotropic-displacement factors to a residual of R

= 0.046. The addition of an isotropic-extinction factor

did not improve the results. Although the |E

2

 – 1| statis-



tic is low for centrosymmetric structures, lowering the

symmetry to P1 did not improve the refinement, nor was

there any indication that the lower symmetry suggested

a better structural model. Use of the program MISSYM

(Le Page 1987) suggests the possible presence of a two-

fold axis. The Laue merging for monoclinic symmetry

is 6.1%. The metric deviation from monoclinic symme-

try is only 0.2

°

, with a 25.72, b 6.260, c 13.085 Å, 



90.19, 


␤ 91.21 and ␥ 89.87. Essentially the same struc-

ture can be refined in C2/c (R = 0.06) with four of the

six H

2

O groups coordinated to the Na site split into two



half-occupied sites each. We view the 0.2

°

 metric devia-



tion, the 6.1% Laue merging and the site splitting in C2/

c as sufficient evidence to rule out monoclinic symmetry.

Table 4 contains the final positional anisotropic-dis-

placement factors and equivalent isotropic-displacement

parameters, and Table 5 contains selected interatomic

distances and angles. Observed and calculated structure-

factors have been submitted to the Depository of Un-

published Data, CISTI, National Research Council of

Canada, Ottawa, Ontario K1A 0S2, Canada.

1457 38#6-déc.00-2203-13

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1463


1464

THE


 

CANADIAN


 

MINERALOGIST

D

ESCRIPTION



 

AND


 D

ISCUSSION

 

OF

 



THE

 S

TRUCTURE



The structure of adamsite-(Y) has four large-cation

sites with two distinct polyhedra. The two Na sites, each

with six-fold coordination, occupy [Na(H

2

O)



6

] polyhe-

dra that may be described as a bifurcated tetragonal

pyramid with the Na atom slightly above the square

base. This base consists of four H

2

O groups, whereas



the bifurcated apex has two additional H

2

O groups. The



nine-fold coordination (seven O atoms and two H

2

O



groups) around each Y site may be described as a

monocapped square antiprism. All (CO

3

) polyhedra



share edges with this (Y

9



) polyhedron (

␾ is an unspeci-

fied ligand).

The crystal structure of adamsite-(Y) is layered on

(001) (Fig. 4). The layering of REE-bearing carbonates

is described in detail by Grice et al. (1994). In adamsite-

(Y), there are thick slabs (Fig. 4) composed of a unit of

Y atoms and parallel “flat-lying” (CO

3

) polyhedra sand-



wiched between layers of Na(H

2

O)



6

 polyhedra and per-

pendicular “standing-on-end” (CO

3

) polyhedra (Grice



et al. 1994). These [NaY(CO

3

)] slabs are H-bonded to-



gether, and it is these H-bonds that give rise to the per-

fect {001} cleavage and the relatively unstable nature

of adamsite-(Y).

Adamsite-(Y), NaY(CO

3

)

2



•6H

2

O, and thomas-



clarkite-(Y), NaY(HCO

3

)(OH)



3

•4H


2

O (Grice & Gault

1998), are found intimately associated with one another

at Mont Saint-Hilaire. These two minerals share simi-

larities in chemical composition and crystal structure.

In both minerals, there is a distinctive fundamental unit

that consists of a stacked, edge-sharing unit of three

polyhedra centered by a C, a Y and a Na atom (Fig. 5).

Although the two sets of polyhedra differ in coordina-

tion number (Y polyhedron) and ligands (OH groups



versus H

2

O groups in both the Na and Y polyhedron),



the fundamental building block is essentially the same.

In adamsite-(Y), the Na–Y–C tri-polyhedra form planes

and have a strong cross-linkage in the (001) plane with

the (YO


9

) polyhedra, sharing corners and edges and

being further reinforced by the “flat-lying” carbonate

groups (Fig. 5a). In thomasclarkite-(Y), the Na–Y–C tri-

polyhedra share edges, forming single chains parallel to

[001] (Fig. 5b).



Genesis of adamsite-(Y)

Adamsite-(Y) occurs as a very late-stage, low tem-

perature, hydrothermal phase within cavities in an alka-

line pegmatite dike in the nepheline syenite intrusion.

In these cavities, adamsite-(Y) appears to crystallize

after rhodochrosite and petersenite-(Ce), is contempo-

raneous with horváthite-(Y) and donnayite-(Y), and pre-

cedes thomasclarkite-(Y), which has been observed as

an epitactic growth on adamsite-(Y) (pers. commun., L.

Horváth). This sequence of crystallization is indicative

of lowering carbonate activity and Lewis basicity. Com-

paring the formulae of the minerals involved shows a

decrease in the ratio of carbonate groups relative to the

number of cations plus the other chemical species in-

volved [(H

2

O), (OH), F]. The lowering of Lewis basic-



ity is effected by the distribution of the H atoms. As H

bonds to O, the basicity decreases; for example, typical

Lewis base strengths (valence units) (O’Keeffe &

Navrotsky 1981) are: (CO

3

)

2–



 0.22, (HCO

3

)



 0.17, O


2–

0.50, (OH)

 0.40, (H



2

O) 0.20. Thus in the transition

from adamsite-(Y) to thomasclarkite-(Y), there is a shift

from a carbonate to a bicarbonate. Grice & Gault (1998)

and Grice (1991) discussed the typical formation of bi-

carbonate minerals at low-temperature, slightly acidic

conditions. Similarly, in this transition, more of the O

atoms become protonated, thus lowering the Lewis base

strength of thomasclarkite-(Y) relative to adamsite-(Y).

1457 38#6-déc.00-2203-13

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1464


ADAMSITE

-(

Y



FROM


 

MONT


 

SAINT


-

HILAIRE


QUEBEC


1465

A

CKNOWLEDGEMENTS



The authors thank Gregory Young and Elizabeth

Moffatt, Canadian Conservation Institute, Ottawa, for

the thermogravimetric and infrared-absorption analyses,

respectively, and Dr. F.C. Hawthorne, University of

Manitoba, for use of the fully automated CCD-equipped

four-circle diffractometer. Dr. Peter Tarassoff gener-

ously provided the specimens that were used in this

study. We also thank László and Elsa Horváth for infor-

mation regarding the occurrence and associated species

of adamsite-(Y), Dr. Andrew McDonald, Laurentian

University, for biographical information on F.D.

Adams, and Dr. Terry Williams, The Natural History

F

IG

. 4.



The adamsite-(Y) structure projected along [010]. Red triangles represent (CO

3

)



polyhedra, the Na atoms are yellow, the Y atoms are orange, and the (H

2

O) groups are



blue. The unit cell is outlined.

F

IG



. 5.

a) The adamsite-(Y) structure projected along [010]

with c vertical. Red triangles represent (CO

3

) polyhedra,



the Na polyhedra are yellow, and the Y polyhedra, orange.

b) The thomasclarkite-(Y) structure projected on [100] with



b vertical. Same color scheme as for adamsite-(Y).

1457 38#6-déc.00-2203-13

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1465


1466

THE


 

CANADIAN


 

MINERALOGIST

Museum, London, for providing the photograph of

adamsite-(Y) shown in Figure 1. The manuscript was

improved by the comments and suggestions of two ref-

erees, Drs. Andrew McDonald and Carlo Gramaccioli

and Editor Dr. Robert F. Martin. This research was made

possible by the Canadian Museum of Nature.

R

EFERENCES



A

DAMS


, F.D. (1903): The Monteregian Hills – a Canadian

petrographical province. J. Geol. 11, 239-282.

C

OTTON


, F.A. & W

ILKINSON


, G. (1980): Advanced Inorganic

Chemistry (4

th

 ed.). Wiley-Interscience, New York, N.Y.



(497-498).

G

RICE



, J.D. (1991): Bicarbonate minerals: crystal chemistry

and geological significance. Geol. Assoc. Can. – Mineral.



Assoc. Can., Program Abstr. 16, A47.

________ & G

AULT

, R.A. (1998): Thomasclarkite-(Y), a new



sodium – rare-earth-element bicarbonate mineral from

Mont Saint-Hilaire, Quebec. Can. Mineral. 36, 1293-1300.

________, V

AN

  V



ELTHUIZEN

, J. & G


AULT

, R.A. (1994):

Petersenite-(Ce), a new mineral from Mont Saint-Hilaire,

and its structural relationship to other REE carbonates. Can.



Mineral. 32, 405-414.

H

ORVÁTH



, L. & G

AULT


, R.A. (1990): The mineralogy of Mont

Saint-Hilaire, Quebec. Mineral. Rec21, 284-360.

L

E

 P



AGE

, Y. (1987): Computer derivation of the symmetry el-

ements implied in a structure description. J. Appl.

Crystallogr. 20, 264-269.

M

ANDARINO



, J.A. (1981): The Gladstone–Dale relationship.

IV. The compatibility concept and its application. Can.



Mineral19, 441-450.

M

OCHIZUKI



, A., N

AGASHIMA


, K. & W

AKITA


, H. (1974): The

synthesis of crystalline hydrated double carbonates of rare

earth elements and sodium. Bull. Chem. Soc. Japan  47,

755-756.


O’K

EEFFE


, M. & N

AVROTSKY


, A. (1981): Structure and Bond-

ing in Crystals. Academic Press, New York, N.Y.

Received June 12, 2000, revised manuscript accepted Septem-

ber 30, 2000.

1457 38#6-déc.00-2203-13



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1466


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