Differentiation between gems and synthetic minerals by laser Raman microspectroscopy

135

Journal of MolecularStructure, 143 (1986) 135-138 ElsevierScience Publkhers B.V., Amsterdam-Printed in The Netherlands

DIFFERENTIATION BETWEEN NATURAL GEMS AND SYNTHETIC

MINERALS

BY LASER RAMAN MICRO-

SPECTKOMETRY.

M.L. DELE-DUBOISl, P. DHAMELINCOURTl, J.P. POIROTZ, H.J. SCHUBNEL3 1 Laboratoire de spectrochimie infrarouge et Raman, LP.2641 CNRS, BStiment C.5 Universite de Lille I, 59655 Villeneuve d'Ascq Cedex, France. 2 Chambre de Commerce et d'Industrie de Paris, Service Public du Contr6le des diamants, des perles fines et des perles precieuses, 2 Place de la Bourse, 75002 Paris, France 3 Museum National d'Histoire Naturelle, 36 rue Geoffroy Saint Hilaire, 75005 Paris, France.

ABSTRACT By allowing positive identification of fluid and solid inclusions inside minerals laser Raman microspectrometry has proved to be a perfect technique for discriminating between natural gems or synthetic minerals made for jewellery (sapphire, ruby, emerald).

INTRODUCTION For the gemmologist importance logical

the identification

both for their authentication

of inclusions

and for the determinatibn

at least partial

destruction

destructive

technique,

any special

studies

sample preparation.

ser beam can be focused clusion

of their geo-

origin.

Prior to the use of the Raman microprobe, involved

in gems is of the utmost

to be recorded.

sis. This last method, to a complete

radiations

through

a crystalline

the Raman spectrum

only an elemental

many solids and fluid inclusions

did not always

lead

With the help of Raman

Available

according

and that of the host in order to minimize

With this technique

were identiprobe analy-

the nature of molecules

spectra.

are 488, 514.5, 647.1 nm. They were choosen

of the inclusion

inclusions

analysis,

to identify

from their vibrational

the la-

of this inclusion

and electron

of the nature of inclusions.

it is now possible

structures

out without

or cut facet into the in-

such as visual observation

identification

of inclusions

that the host gem is transparent

thus allowing

furnishing

techniques

and polyatomic

Provided

in gems may be carried

Prior to the use of the Raman microprobe

fied by the use of methods

microprobing

identification

of gems.. Now by using this "in situ" non

of inclusions

directly

to be characterized,

positive

excitation

to the nature

fluorescence.

in gems have been studied.

In previous works a large variety of inclusions have been identified for example : - Chromite, forsterite, mond

iron oxyde,

graphite,

garnet

(Ref. 2).

oO22-2860/86/$03.50

0 1986 ElsevierScience PublishersB.V.

(Ref. l), diopside

in dia-

136 - Oligoclase,

monazite,

te, rutile

pargasite,

phlogopite,

zircon, apatite,

albi-

(Ref. 3) in sapphire.

- Sphalerite, - Apatite,

britholite,

calcite,

pyrite,

nepheline,

amphibole

fassarte

in ruby.

(Ref. 3), N2, CO2 and hydrocarbons

in emerald

(Ref. 2). The results lid inclusions diamond", Columbia

presented ranging

sapphire

here include

positive

from Australia

and Columbia,

and on the other hand in synthetic

Flux fusion method

(CHATHAM, GILSON,

KASHAN) and hydrothermal

method

I. INCLUSION

GEMS

IN NATURALS

A diamond which particles

or tentative

from one to fifty microns

Ruby from Africa,

minerals

LENNIX,

identification

in size in several

obtained

KNISCHKA,

gems

of so-

: "star

Emerald

from

by two methods

RAMOURA,

SEIKO,

:

IGMERALD,

(LINDE).

is cut along the A3 axis exhibit

which form dark areas seeming arranged

numerous

blackish

included

in the cut plates at angle of

120'. They are inclusions of graphite. Only the Raman line at 1580 cm-I is obser-1 ved as the second graphite line occuring at 1360 cm is completely masked by the -1 very intense 1332 cm diamond line. In the same diamond a rare fluid inclusion of nitrogen, -1

cm

one micron

size, has been characterized

by the Raman line at 2342

.

In a sapphire

from Columbia

the spectra were recorded

from an inclusion

of apa-

tite inside an inclusion of zircon. These compounds were identified by their line -1 -1 -1 at 963 cm and 437-356 cm for apatite and at 1009 cm for zircon. In a sapphire

from Australia

noting that for the included

inclusion

of zircon was also found.

It is worth

zircon a shift of several wavenumbers in the posi-1 was observed. It could be related to a pres-

tion of the Raman line at 1009 cm sure effect

that is very interesting

have been brought revealed

up to surface

otherwise

in their crossing

to observe

by volcanic

by mechanical

macles.

because

eruption.

in both cases sapphires

This explains

Theses macles exhibit

the stress

some hollow canals

; nothing was found inside except iron oxydes as it was fore-

seen. An inclusion a shift towards doublet.

of chromite

was identified

higher frequencies

inside a ruby from Africa.

was observed

This shift must be related

for'the

to a different

in Cr203, MgO, A1203 and Fe0 + Fe203 compared found in diamond

(Ref. 4). In another

found exhibiting

characteristic

caracteristic

composition

600-700

cm

-1

of the chromite

to the same chromite

Ruby from Africa

However

an inclusion

inclusion of Pyrite was

Raman lines at 438, 380 and 344 cm-l.

In an emerald from Siberia inclusion of Rutile was characterized by doublet at -1 612 and 447 cm . It is worth noting that Raman spectra permit also the identification of the different Calcite

polymorph

was also identified

of Ti02

(Rutile, anatase,

in the same emerald

(Fig. 1).

Brookite)

(Ref. 5).

137

Lalci>

I 1000

fl

&d Fig. 1

II.

600

800

LOO

200

: Spectrum of calcite inclusion in an emerald from Columbia

INCLUSIONS IN SYNTHETIC MINERALS In synthetic

crystals

cutable

found to be very different Inclusions tly studied.

in synthetic Transparent

from those analyzed minerals

inclusions

and from "Seiko" were identified Si-0 stretch

tic emerald

from "Igmerald",

In a Chatham

were

gems.

inside both synthetic

emeralds

from "Gilson"

from the sharp line at 876 cm -I of

as polymolybdate

"Gilson",

synthetic

A frequency

shift of the principal

stone to another.

Chatham

emerald

looked

formed

in natural

inclusions

made by flux fusion methods were subsequen-

as Phenakite

sions which

the acidity

as expected,

and three weak lines at 948, 920, 914 cm-l. On the other hand inclu-

sions of solvant were identified

Chatham.

for jewellery,

of the solution

minerals

; synthetic Ruby from Knishka and

were in fact identified

as polymolybdate.

line (960 to 940 cm-') was observed

solutions

this variation

in frequency

(Ref. 6). Here we may suppose either

from melts at different

: synthe-

"the cloud" formed by very small inclu-

like fluid inclusions

In aqueous

in different

pH or mixture

of polymolybdates

from one

is linked to

solid solutions

involving

diffe-

rent cations.

In a synthetic

ruby made by "Kashan"

710, 270, 144 cm-l were identified "Ramoura"

inclusions

360 and 330 cm inclusions

-1

. By comparison

were found to contain Raman spectra

as carbonates.

of orthovonodates

are probably

some inclusions

with spectra

two types of inclusions

show that the transparent

In two synthetic

were identified

sodium orthovanadate.

exhibiting

(transparent

of Moo3 in variable

proportions.

emerald

exhibited

inclusions

these emeralds

and dark in colour).

ones are quartz with

the dark ones, more or less colored,

synthetic

orthovanadates,

the Lemix synthetic

and beryls, whereas

Sometimes

rubies from

by the Raman lines at 827,

of different Finally

lines at 1084,

line at 464 cm-l

are mixture

of polymorphs

of quartz in the same -1 Raman lines at 820 and 998 cm indicative of traces

138 of orthorhombic

Moo3 (Ref. 7). Up to now the dark blue inclusions

to be metallic

Platinum.

Raman spectroscopy

The presence

were assumed

of this metal cannot be confirmed

because metals which are totally opaque materials

using

to visible

light do not yied Raman spectra. On the other hand in synthetic Phenakite

(without

and perhaps

Obj. 100 I

I

the best method

for discriminating

absence

X = 488 nm

C02). Raman

is then an easy

natural emerald

between

and hydro-

synthetic

according

method

I

with a water filled

spectroscopy

thermal

"Linde" made by hydrothermal

(Fig. 2) was found

associated cavity

Emerald

II

I

emerald

to the presence

of phenakite

or

and C02.

e

A%m”

’

’

Fig. 2

CONCLUSION

*

800

’

’

600

’

’

’

MO

200

: Spectrum of Phenakite inclusion in "Linde" synthetic

emerald.

This work show that micro Raman spectroscopy inclusions

is a choice method

inside gems. However

rial, are too opaque, gnal stronger

for "in situ" non destructive

difficulties

fluorescent

are sometimes

or when inclusions

than that of the host (low density

analysis

encountered

are to small to yield

gas inclusion,

of

when matea si-

small or deep in-

clusion). Mrs Bettetini,

Hlnni, Lagache,

Vincent

nished samples of some of the minerals

are very acknoledged

which

for having

fur-

have studied.

REFERENCES Del+Dubois M.L., Dhamelincourt P., Schubnel H.J., XI General Meeting of International Mineralooical association, Novosibirsk URSS. 1978. Revue-Francaise de gemmoloDel&Dubois M.L., Dhamelincourt P. Schubnel H.J., gie, 1981, no 63, p. 11-14, no 64, p. 13-16. M.L. Del&Dubois, l&e Conference Europeenne des Pierres Precieuses de couleurs, Anvers, Octobre 1983. Malezieux J.M., Barbillat J., C.R. Acad. Sci. Paris, 1980, t.271, serie D, p. l-3. Clarence Karr, I.R. and Raman spectroscopy of lunar and terrestrial minerals. Academic Press, New York. Katsuo Murata, Shigero Ikeda, Spectrochimica Acta, vol. 39 A, no 9, p.787-794, 1983. Payen E., These, Lille, 1983.