Eu . J. Mine al., 37, 53–62, 2025
h ps://doi.o g/10.5194/ejm-37-53-2025
© Au ho (s) 2025. This wo k is dis ibu ed unde
he C ea i e Commons A ibu ion 4.0 License.
Finge p in ing o uby and sapphi e gems ones h ough
Fou ie - ans o m in a ed (FTIR) me hodologies
An ónio Soa es de Sousa1, Elsa Ma ia Ca alho Gomes2, Lau a Bayés-Ga cía1,
Alessand a Di Ma iano1, and Mai e Ga cia-Valles1
1Depa amen de Mine alogia, Pe ologia i Geologia Aplicada, Uni e si a de Ba celona,
Ba celona 08028, Spain
2Cen e o Ea h and Space Resea ch o he Uni e si y o Coimb a – CITEUC, Depa men o Ea h Sciences,
Facul y o Sciences and Technology, Uni e si y o Coimb a, Rua Síl io Lima, 3030-790 Coimb a, Po ugal
Co espondence: An ónio Soa es de Sousa (lopessoa [email protected])
Recei ed: 4 July 2024 – Re ised: 14 No embe 2024 – Accep ed: 12 Decembe 2024 – Published: 7 Feb ua y 2025
Abs ac . Gems ones ha e signi ican economic, cul u al, and a is ic alue. Ad ances in he ea men and
p oduc ion o syn he ic gems ones c ea e he need o mo e p ecise iden i ica ion me hods o dis inguish na u al
s ones om hei syn he ic and ea ed coun e pa s. Fou ie - ans o m in a ed (FTIR) spec oscopy, a non-
des uc i e echnique, is widely employed in ad anced gemological analysis. In his s udy, 25 ubies and sap-
phi es (na u al, syn he ic, and ea ed) om he Gemology School o he Uni e si y o Ba celona we e analysed
using s anda d gemological ins umen s and FTIR spec oscopy. Dis inc spec al inge p in s we e iden i ied o
di e en ca ego ies and ea men s. Un ea ed na u al s ones showed a band a 3230 cm−1(wi h an addi ional
peak a 3310 cm−1in sapphi es), whe eas Ve neuil specimens showed peaks a 3185, 2230, and 3310 cm−1(wi h
his las peak being mo e in ense he one a 3310 cm−1in sapphi es), and lux specimens showed a 3310 cm−1
band. Rega ding ea ed gems ones, di usion- ea ed samples showed a ain band cen ed a 3310 cm−1; he
glass- illed ones exhibi ed cha ac e is ic bands a 2250, 2600, and 3300 cm−1; and he ea ed Ve neuil uby
showed a band cen ed a 3310 cm−1. These spec al inge p in s can be used o dis inguish be ween na u al,
syn he ic, and ea ed ubies and sapphi es and con ibu e o exis ing da abases, allowing o simple and as e
gemological analysis in u u e s udies.
1 In oduc ion
The in e es gene a ed by gems ones is well known, no only
om a comme cial pe spec i e bu also om a cul u al and
a is ic poin o iew (Hughes, 1990). One o he mos signi -
ican gems ones is co undum, which consis s o c ys allised
alumina (Al2O3). As an alloch oma ic mine al, co undum is
comple ely colou less in i s pu e s a e, wi h i s colou esul -
ing om mino impu i ies. The e m uby is used o e e
o i s ib an - ed o pu plish- ed colou a ie y, ela ed o C
impu i ies in i s s uc u e. All he o he colou s belong o he
sapphi e a ie y, in which he blue colou is due o he p es-
ence o Fe and Ti (Dubinsky e al., 2020; Hughes, 1997).
To mee he cu en g owing ma ke demand, imp o e-
men s in echniques and echnologies ha e led o an in-
c ease in he p oduc ion capaci y o syn he ic gemological
ma e ial in he labo a o y (Pellice , 2001; Shigley, 2000). As
desc ibed by Nassau (1980), he mos well-known g ow h
echniques used a e hose om a mel (e.g. Ve neuil) and
om a solu ion (e.g. lux). In addi ion o hese syn heses,
he modi ica ion o ce ain physicochemical p ope ies o
lowe -quali y gems ones is common, o bo h imp o e ce -
ain cha ac e is ics alued in na u al gems ones and c ea e
subs i u es (Roselló, 2004). Hea ea men , i adia ion, im-
p egna ion, dyeing, and coa ing a e some o hese ea men s,
which a e desc ibed well by Nassau (1984). In many cases,
he in o ma ion on he ea men and syn hesis me hods used
is no dissemina ed, and, al hough hey o en display dis inc-
i e gemological cha ac e is ics, some ea ed and syn he ic
gem ma e ials can be di icul o iden i y (Shigley, 2000).
Published by Cope nicus Publica ions on behal o he Eu opean mine alogical socie ies DMG, SEM, SIMP & SFMC.
54 A. Soa es de Sousa e al.: Finge p in ing o uby and sapphi e gems ones
In his con ex , based on a cons an ly e ol ing indus y, i
has become an essen ial and necessa y ask o gemological
labo a o ies o de elop a me hodology ha allows he es ab-
lishmen o p o ocols o he p ecise iden i ica ion o hese
ma e ials, he di e en ia ion be ween na u al and syn he ic
coun e pa s, and he de ec ion o speci ic ea men s.
While classical me hods o gemological cha ac e isa ion
and s udy ha e ce ain limi a ions in his ask, Fou ie -
ans o m in a ed (FTIR) spec oscopy, a non-des uc i e
me hod based on he de ec ion o molecula ib a ions, has
p o en o be a echnique wi h g ea po en ial. T adi ion-
ally used on o he ma e ials o a a ie y o pu poses, his
echnique ep esen s a e y signi ican ad ance in he s udy
o gemological ma e ials, including co undum, allowing he
iden i ica ion o he mine als and hei impu i ies (Hain-
schwang and No a i, 2008). As a nominally anhyd ous min-
e al, co undum can inco po a e a ce ain amoun o hyd o-
gen in he o m o s uc u al OH g oups, which can be ob-
se ed using in a ed spec oscopy. This allows us o ob ain
e y aluable in o ma ion abou a gems one in a sho ime
(Balan, 2020). FTIR spec al inge p in s can also be used as
a e e ence o u u e analyses, making i possible o com-
pa e he spec al in o ma ion o di e en s ones (F i sch and
S ock on, 1987).
In o de o con ibu e o a simple and as e app oach
o he iden i ica ion o gem-quali y co undum, in his s udy,
he spec al inge p in s o a g oup o 25 na u al, syn he ic,
and ea ed ubies and sapphi es belonging o he Gemol-
ogy School o he Uni e si y o Ba celona a e es ablished
using FTIR spec oscopy. The analysis was complemen ed
by a s anda d gemological cha ac e isa ion.
2 Ma e ials and me hods
A o al o 25 ubies and sapphi es belonging o he Gemol-
ogy School o he Uni e si y o Ba celona we e selec ed o
his s udy, whose ela ed mic oscopy images a e shown in
Fig. 1. Sample IDs we e de ined by speci ying he s one a-
ie y (R o uby, S o sapphi e) ollowed by hei o igin
(N o na u al, S o syn he ic). Addi ionally, T was used o
e e o ea ed gems ones. This se consis ed o six na u al
ubies, se en syn he ic ubies, six na u al sapphi es, and six
syn he ic sapphi es.
S anda d gemological ins umen s we e used o measu e
s one p ope ies. A combina ion o long- (365 nm) and sho -
wa e (254 nm) Ray ech ul a iole (UV) lamps we e used o
luo escence obse a ions. Mic oscopic obse a ion was pe -
o med using a Mo ic GM-171 mic oscope, wi h a magni i-
ca ion capaci y o 3.75× o 25×, equipped wi h a da k- ield,
b igh - ield, and o e head illumina ion sys em and a Mo i-
cam S6 came a.
FTIR spec oscopy was pe o med using a Pe kinElme
F on ie FTIR spec ome e equipped wi h an op ical po as-
sium b omide (KB ) beam spli e and a iglycine sul a e
(TGS) de ec o , adap ed wi h a di use e lec ance acces-
so y. The spec a be ween 400 and 4000 cm−1we e ob-
ained h ough 32 scans, and he esolu ion was se a 4 cm−1,
wi h 1.928 cm−1da a spacing. Be o e each measu emen ,
he spec ome e was calib a ed wi h KB . Spec a we e col-
lec ed using he Pe kinElme Spec um so wa e.
I is well known ha spec a a e closely ela ed o he way
he inciden adia ion passes h ough each s one. Then, ac-
o s such as posi ion, cu , size, anspa ency, ac u es, and
inclusions can la gely a ec he spec al ou pu (Thongnop-
kun and Ekgasi , 2005). To ensu e high-quali y esul s and
o assess he in luence o sample posi ioning on spec al da a
consis ency, a iables such as he gems one o ien a ion and
placemen on he spec ome e we e es ed. The op imal po-
si ion was adjus ed acco ding o he speci ic cha ac e is ics
o each sample, and he xposi ions o he abso p ion peaks
we e analysed o e i y consis ency.
3 Resul s and discussion
3.1 Gemological p ope ies
The analysed s ones p esen ed masses anging om 0.238
o 8.174 c . The cu s we e mos ly mixed. Some s ones a -
ied be ween b illian , s ep, o cabochon cu s. The colou s o
he ubies anged om ed o pu plish ed, while he sap-
phi es anged om pale pu ple o blue (see Table 1). Mos o
he s ones we e anspa en , excep o s ones RN2 and RS4,
which we e opaque, and RNT1, RNT2, and SNT1, which
we e anslucen due o he glass- illed issu es.
Re ac i e indexes we e hose ypical o co undum, wi h a
sligh inc ease in s one SNT1 due o he p esence o cobal
glass (1.765–1.773) (Leelawa anasuk e al., 2013). S ones
RNT1 ( illed wi h lead glass), RNT2, and SNT1 ( illed wi h
cobal glass) had a highe speci ic g a i y (4.02, 4.18, and
4.08).
Rega ding he esponse o gems ones o UV adia ion, na -
u al ubies exhibi ed a weak o e y s ong ed colou un-
de long-wa e adia ion (365 nm). The weak ed shown by
uby RNT1 was caused by he p esence o lead glass (Pa -
dieu, 2010). Syn he ic ubies showed a e y s ong ed, and
sapphi es we e all ine excep o s one SNT1, which was
illed wi h cobal glass. This s one exhibi ed a weak o ange-
ed colou , also obse ed by Leelawa anasuk e al. (2013),
cha ac e is ic o cobal -glass- illed sapphi es. All he s ones
we e ine unde sho -wa e UV adia ion (254 nm).
As o pleoch oism, all ubies showed pu ple o ed dich o-
ism, and na u al and syn he ic sapphi es showed signi ican
di e ences in his espec . Na u al sapphi es exhibi ed blue
o iole -blue dich oism, while a iole -blue o g eenish-blue
dich oism was obse ed in syn he ic sapphi es. S ones RNT1
and SNT1 showed weake dich oism, which Leelawa ana-
suk e al. (2013, 2015) a ibu ed o he iso opy o he glass.
Abso p ion spec a showed he expec ed cha ac e is ics o
he di e en a ie ies o co undum, excep o s one SNT1.
Eu . J. Mine al., 37, 53–62, 2025 h ps://doi.o g/10.5194/ejm-37-53-2025
A. Soa es de Sousa e al.: Finge p in ing o uby and sapphi e gems ones 55
Figu e 1. (a) Na u al uby RN1, (b) na u al uby RN2, (c) na u al uby RN3, (d) na u al uby RN4, (e) na u al uby (glass- illed) RNT1,
( ) na u al uby (glass- illed) RNT2, (g) syn he ic uby (Ve neuil) RS1, (h) syn he ic uby (Ve neuil) RS2, (i) syn he ic uby (Ve neuil) RS3,
(j) syn he ic uby (Ve neuil) RS4, (k) syn he ic uby ( lux) RS5, (l) syn he ic uby ( lux) RS6, (m) syn he ic uby ( lux) RS7, (n) na u al
sapphi e SN1, (o) na u al sapphi e SN2, (p) na u al sapphi e (glass- illed) SNT1, (q) na u al sapphi e (di usion- ea ed) SNT2, ( ) na u al
sapphi e (di usion- ea ed) SNT3, (s) na u al sapphi e (di usion- ea ed) SNT4, ( ) syn he ic sapphi e (Ve neuil) SS1, (u) syn he ic sapphi e
(Ve neuil) SS2, ( ) syn he ic sapphi e (Ve neuil) SS3, (w) syn he ic sapphi e ( lux) SS4, (x) syn he ic sapphi e ( lux) SS5, and (y) syn he ic
sapphi e ( lux) SS6. O e head illumina ion, 3.75×.
This cobal -glass- illed sapphi e showed abso p ion bands
be ween 500 and 565, 580 and 600, and 630 and 660 nm,
ypical o cobal glass (de Mi anda Pin o e al., 2011), and a
weak line a 450 nm, co esponding o he p esence o i on in
he sapphi e.
The mic oscopic images o selec ed ubies and sapphi es
a e shown in Fig. 2. Mic oscopic obse a ion e ealed he
p esence o u ile inclusions as he main cha ac e is ic o
he un ea ed na u al specimens. These we e p esen in he
o m o needles, pa icles, and angula bands o ming along
g ow h ea u es. Pa ially healed issu es and ension halos
we e also de ec ed. In addi ion, hese s ones con ained a a-
ie y o uniden i ied mine al inclusions (Fig. 2a). Appa en
py ochlo e c ys als we e obse ed in s one SN1, sugges ing
a na u al basal ic o igin (Soon ho n an ikul e al., 2019) (see
Fig. 2b).
h ps://doi.o g/10.5194/ejm-37-53-2025 Eu . J. Mine al., 37, 53–62, 2025
56 A. Soa es de Sousa e al.: Finge p in ing o uby and sapphi e gems ones
Table 1. Gemological p ope ies o he cha ac e ised s ones.
ID Va ie y T ea men Colou Cu Dimensions (mm) Weigh
(c )
RN1 Na u al uby Pu plish- ed Pea mixed 3.39 ×4.77 ×1.88 0.238
RN2 Na u al uby Pu plish- ed O al cabochon 10.52 ×9.55 ×7.31 7.515
RN3 Na u al uby Pu plish- ed O al mixed 4.02 ×5.18 ×2.49 0.475
RN4 Na u al uby Pu plish- ed O al mixed 3.69 ×4.43 ×1.81 0.263
RNT1 Na u al uby Lead-glass- illed O angey- ed O al mixed 5.70 ×9.42 ×3.29 1.939
(majo )1
RNT2 Na u al uby Glass- illed2Pu plish- ed O al b illian 6.25 ×9.22 ×4.01 2.324
(medium)
RS1 Syn he ic uby (Ve neuil) Red O al b illian 4.08 ×6.04 ×2.71 0.571
RS2 Syn he ic uby (Ve neuil) Red Squa e mixed 6.38 ×6.65 ×2.98 1.283
RS3 Syn he ic uby (Ve neuil) Red Round b illian 6.08 ×6.01 ×3.79 0.998
RS4 Syn he ic uby (Ve neuil) Pu plish- ed Round cabochon 8.95 ×8.89 ×4.25 3.493
(as e ism)
RS5 Syn he ic uby ( lux) Red O al b illian 4.00 ×5.95 ×2.66 0.534
RS6 Syn he ic uby ( lux) Red Round b illian 6.93 ×6.91 ×4.28 1.608
RS7 Syn he ic uby ( lux) Red O al mixed 4.60 ×6.43 ×3.21 0.898
SN1 Na u al sapphi e Blue O al mixed 4.56 ×5.15 ×3.42 0.675
SN2 Na u al sapphi e Da k-blue Rec angle s ep 4.17 ×5.09 ×2.59 0.524
SNT1 Na u al sapphi e Cobal -glass- illed Da k-blue O al mixed 9.85 ×11.95 ×5.13 5.119
(medium)
SNT2 Na u al sapphi e Di usion Pu plish-blue Round mixed 5.06 ×4.99 ×2.99 0.550
SNT3 Na u al sapphi e Di usion Da k-blue O al mixed 4.33 ×5.64 ×2.01 0.491
SNT4 Na u al sapphi e Di usion Blue O al cabochon 3.91 ×5.17 ×2.18 0.507
SS1 Syn he ic sapphi e (Ve neuil) Pu plish-blue Rec angle s ep 7.04 ×8.99 ×4.20 2.948
SS2 Syn he ic sapphi e (Ve neuil) Da k-blue O al b illian 4.10 ×5.97 ×2.79 0.628
SS3 Syn he ic sapphi e (Ve neuil) Ligh -blue O al mixed 11.58 ×12.68 ×5.18 8.174
SS4 Syn he ic sapphi e ( lux) Pu plish-blue O al b illian 6.02 ×7.99 ×3.90 1.499
SS5 Syn he ic sapphi e ( lux) Pale-pu ple O al b illian 4.90 ×6.90 ×3.21 0.984
SS6 Syn he ic sapphi e ( lux) Pu plish-blue O al cabochon 7.31 ×9.05 ×4.61 3.367
1The e ms “majo ” and “medium” a e ela ed o he quan i y o glass p esen in he s one, judging by isual inspec ion. 2I was no possible o de e mine he ype o glass
used o ea his s one.
Glass- illed s ones showed a cloudy appea ance and zones
o colou concen a ion wi h an i idescen e ec on he in-
e nal issu es as hei main cha ac e is ics. Se e al ypical
apped gas bubbles we e also de ec ed in he illed issu es
(Fig. 2c, d). The su aces o hese s ones showed di e ences
in elie and lus e (Kane, 1984).
Di usion- ea ed na u al sapphi e showed e y ine u ile
pa icles. The size o he u ile c ys als and he absence o
o he inclusions we e indica i e o he high empe a u es o
which he sample was subjec ed (Emme e al., 2003).
Apa om he cabochon-cu s ones, all Ve neuil speci-
mens exhibi ed cu ed g ow h ma ks (Fig. 2e), wi h gas bub-
bles isible in some samples (Fig. 2 ).
Eu . J. Mine al., 37, 53–62, 2025 h ps://doi.o g/10.5194/ejm-37-53-2025
A. Soa es de Sousa e al.: Finge p in ing o uby and sapphi e gems ones 57
Figu e 2. (a) Bands o u ile pa icles and pa ially healed issu es in na u al uby RN3 (da k- ield illumina ion, 25×). (b) Red c ys als in
na u al sapphi e SN1 (possibly py ochlo e) (da k- ield illumina ion, 25×). (c) In e nal issu es wi h a cloudy appea ance and gas bubbles in
glass- illed uby RNT1 (da k- ield illumina ion, 15×). (d) In e nal issu es wi h colou concen a ion and gas bubbles in glass- illed sapphi e
SNT1 (da k- ield illumina ion, 15×). (e) Cu ed g ow h ma ks in Ve neuil uby RS3 (da k- ield illumina ion, 15×). ( ) Gas bubbles isible in
Ve neuil sapphi e SS2 (da k- ield illumina ion, 25×). (g) Flux esidue in lux-g own uby RS5 (da k- ield illumina ion, 20×). (h) Hexagonal
opaque inclusion in lux-g own uby RS5 (possibly pla inum)(o e head illumina ion, 25×).
The mos dis inc i e aspec o he lux-g own syn he ic
specimens was he p esence o lux esidue (Fig. 2g). Ad-
di ionally, s one RS5 showed a hexagonal opaque inclusion,
mos likely pla inum o igina ing om he g ow h c ucible,
which is ypical o specimens om his syn hesis (Fig. 2h)
(Gubelin and Koi ula, 2004; Pellice , 2001).
3.2 FTIR
In Table 2, he main abso p ion FTIR peaks and bands ob-
se ed o each s one a e summa ised.
All he s ones showed he cha ac e is ic peaks o Al2O3.
These peaks we e loca ed a 485, 515, and 630 cm−1and
we e a ibu ed o he s uc u al ib a ions o Al–O (Chen e
al., 2021). Figu e 3 shows hese peaks clea ly isible in he
sapphi e SN1 spec um.
A se ies o peaks a ound 2350 cm−1we e also exhibi ed
by all gems ones, which may be associa ed wi h CO2 om
luid inclusions and/o a mosphe ic CO2, un ela ed o he
s one (Ka an oni e al., 2021).
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58 A. Soa es de Sousa e al.: Finge p in ing o uby and sapphi e gems ones
Table 2. Main abso p ion peaks and bands in he FTIR spec um (in cm−1) o he s ones and hei causes.
Na u al uby Na u al sapphi e Syn he ic uby Syn he ic sapphi e Assignmen ∗
RN1 RN2 RN3 RN4 RNT1 RNT2 SN1 SN2 SNT1 SNT2 SNT3 SNT4 RS1 RS2 RS3 RS4 RS5 RS6 RS7 SS1 SS2 SS3 SS4 SS5 SS6
3696 3681 3696 3696 3696 OH
3647 3647 3647 3647 3648 3647 3647 3647 3647 3647 OH
3565 3565 3565 3565 OH
3310 3310 3300 3310 3310 3309 3310 3310 3310 3310 3315 3309 3310 3308 3310 3310 3305 OH
3298 3300 3296 H2O
3280 OH
3238 3233 3240 3220 3232 3232 3233 3232 3232 2230 OH
3186 3185 3186 3180 3180 3180 OH
3164 OH
2960 2955 2955 C–H
2899 2910 2922 2920 2918 2918 2916 2916 2918 C–H
2853 2850 2850 2848 2850 2848 2850 C–H
2606 2600 2590 Si–OH
2354 2351 2351 2350 2349 2352 2355 2355 2356 2355 2351 2347 2351 2357 2355 2350 2350 2350 CO2
2319 2331 2326 2326 2340 2340 2340 2328 2344 2332 2318 2325 2326 2336 2340 CO2
2250 2230 2250 Si–OH
631 632 631 637 640 630 630 644 643 641 643 640 630 631 641 630 630 630 645 620 630 Al–O
516 514 507 514 514 516 512 510 514 517 515 512 516 510 508 516 514 512 513 515 520 Al–O
483 485 485 486 490 490 484 486 485 486 483 485 484 485 484 484 483 490 490 485 486 490 480 490 Al–O
∗Balan (2020), Be an and Rossman (2006), Bidny e al. (2010), Ca ie (2009), Chen e al. (2021), E imo e al. (2003), Ka an oni e al. (2021), Kuma and Boe ge (2014), Leelawa anasuk e al. (2013), Mona umi e al. (2014), Phlay ahan e al. (2018), Saengbuangamlam and Buppa enoo (2022),
Scholze (1991), Se o (2012), Soon ho n an ikul e al. (2019), and Volyne s e al. (1972).
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A. Soa es de Sousa e al.: Finge p in ing o uby and sapphi e gems ones 59
Table 3. Cha ac e is ic abso p ion peaks and bands o he di e en a ie ies and ea men s o uby and sapphi e.
T ea men Va ie y Peaks/bands (cm−1)
Na u al – (n=6)∗Ruby Band a 3230
Sapphi e Band a 3230 and a peak a 3310
Di usion (n=3) Sapphi e Fain band a 3310
Glass- illed (n=3) Ruby Bands a 2250, 2600, and 3300
Sapphi e
Syn he ic – (n=6) Ve neuil uby Peaks a 3185, 3230, and 3310
Ve neuil sapphi e
Hea (n=1) Ve neuil uby Band a 3310
– (n=6) Flux uby Band a 3310
Flux sapphi e
∗nmeans he numbe o samples analysed.
Figu e 3. Al2O3peaks obse ed in he FTIR spec um o he sap-
phi e SN1 in he 900–400 cm−1 egion.
Figu e 4 shows cha ac e is ic FTIR spec a o gem-
s ones analysed in his wo k wi hin he egion om 4000 o
2000 cm−1.
Ve neuil specimens showed abso p ion peaks a 3185,
3230, and 3310 cm−1(see Fig. 4a, b). Acco ding o Be an
and Rossman (2006), hese may be associa ed wi h OH bonds
in he s one’s s uc u e. The 3310 cm−1peak became mo e
in ense in sapphi es (Fig. 4a). Phlay ahan e al. (2018) ela ed
his peak o he p esence o TiO2in co undum, a ibu ing i
o he s e ching o he Ti–OH bonds. Al hough no a de e -
mining ac o in he iden i ica ion o a Ve neuil specimen,
he p esence o hese h ee peaks may be a good indica o o
a syn he ic ma e ial, as i is less common in un ea ed na u al
specimens (Be an and Rossman, 2006).
In addi ion o hose men ioned abo e, Ve neuil uby RS2
showed addi ional peaks a 3160 and 3280 cm−1. Volyne s
e al. (1972) also epo ed hese peaks in Ve neuil syn he ic
co undum, ela ing hem o s uc u al OH.
Ve neuil uby RS4 only showed a weak abso p ion
band cen ed a 3310 cm−1. Mona umi e al. (2014) de-
sc ibed he disappea ance o he 3184, 3237, and 3309 cm−1
peaks in Ve neuil specimens a e high- empe a u e ea -
men (1650 °C). This was a ibu ed o he b eaking o me al–
OH bonds. The spec a o hese specimens also exhibi ed
wo s ong addi ional peaks a 2850 and 2918 cm−1and an-
o he less in ense one a 2955 cm−1, which we e assigned
o C–H s e ching ib a ions. Gi en he high in ensi y o he
peaks, hey could ha e been caused by he p esence o a -
i icial esin. K zemnicki (2018) epo ed simila peaks in a
uby illed wi h a i icial esin (Fig. 4c).
The lux specimens (RS5 and SS4) showed an abso p ion
band cen ed a 3310 cm−1(Fig. 4d, e). The lack o cha -
ac e is ic peaks in he OH egion (3100–3600 cm−1) (Be an
and Rossman, 2006) helped o con i m hei syn hesis. Flux
specimens a e syn hesised om pu e Al2O3, wi h he addi-
ion o some me allic elemen s, and a e ee o OH o H2O
in hei composi ion (Bidny e al., 2010; Kane, 1982).
All un ea ed na u al s ones exhibi ed a b oad abso p ion
band, wi h a maximum a 3230 cm−1associa ed wi h s uc-
u al OH (Fig. 4 , g). In sapphi es, hese bands showed a peak
a 3310 cm−1(Fig. 4g). As wi h Ve neuil sapphi es, he di -
e ence be ween he wo a ie ies may be caused by TiO2.
Di usion- ea ed na u al sapphi es showed an almos un-
de ec able band cen ed a a ound 3310 cm−1(Fig. 4h). The
high empe a u es o which he s ones a e subjec ed by his
ea men may cause he emo al o hyd ogen in he s one
and, consequen ly, a dec ease in he abso p ion ela ed o OH
bonds (Emme e al., 2003).
Typical abso p ion bands a 2250, 2600, and 3300 cm−1
o glass- illed co undum (Leelawa anasuk e al., 2013; Pa -
dieu, 2010) we e disce ned in na u al ubies (RNT1 and
RNT2) and sapphi e (SNT1) ha we e subjec ed o his ea -
men (Fig. 4i, j). Among hese signals, Scholze (1991) a -
ibu ed he band a 3300 cm−1 o he abso p ion o wa e
molecules. The bands a 2250 and 2600 cm−1we e ela ed
o Si–OH ib a ions (E imo e al., 2003). They we e mo e
h ps://doi.o g/10.5194/ejm-37-53-2025 Eu . J. Mine al., 37, 53–62, 2025
60 A. Soa es de Sousa e al.: Finge p in ing o uby and sapphi e gems ones
Figu e 4. FTIR spec a o Ve neuil sapphi e SS1 (a), Ve neuil uby RS3 (b), Ve neuil uby RS4 (c), lux uby RS5 (d), lux sapphi e SS4 (e),
un ea ed na u al uby RN2 ( ), un ea ed na u al sapphi e SN1 (g), di usion- ea ed na u al sapphi e SNT2 (h), glass- illed uby RNT1 (i),
and glass- illed sapphi e SNT1 (j) in he 4000–2000 cm−1 egion.
in ense in sample RNT1, which is consis en wi h he amoun
o glass p esen in he s one, as judged by isual inspec ion.
Acco ding o Se o (2012), he ampli ude o he bands e-
lec s he amoun o glass p esen in he gems one.
Table 3 summa ises all he cha ac e is ic abso p ion bands
o he di e en ypes o uby and sapphi e analysed.
As shown, all un ea ed gems ones p esen ed a band
a 3230 cm−1, wi h an addi ional peak in sapphi es a
3310 cm−1. Na u al di usion- ea ed sapphi es showed an
almos unde ec able band a 3310 cm−1, whe eas ypical
b oad bands o hose ha we e glass- illed occu ed a 2250,
2600, and 3300 cm−1. Rega ding Ve neuil samples, a se-
Eu . J. Mine al., 37, 53–62, 2025 h ps://doi.o g/10.5194/ejm-37-53-2025
A. Soa es de Sousa e al.: Finge p in ing o uby and sapphi e gems ones 61
ies o peaks a 3185, 3230, and 3310 cm−1we e obse ed,
wi h he peak a 3310 cm−1being mo e in ense in sapphi es.
Among hem, a Ve neuil uby wi h e idence o hea ing ea -
men (RS4) exhibi ed a band cen ed a 3310 cm−1. Finally,
syn he ic- lux gems ones showed a band a 3310 cm−1.
4 Conclusions
We examined a se o 25 ubies and sapphi es, bo h na u al
and syn he ic, using FTIR spec oscopy o es ablish a eli-
able me hodology o dis inguishing na u al om syn he ic
s ones, as well as iden i ying di e se ea men s.
Gemological analysis and FTIR spec oscopy e ealed
dis inc cha ac e is ics in he specimens o di e en a ie ies
and ea men s, wi h he samples showing speci ic cha ac e -
is ic bands and peaks.
The esul s ob ained pe mi ed us o dis inguish na u al u-
bies and sapphi es om hei syn he ic coun e pa s o om
hose ha ha e unde gone some kind o ea men . These
spec al inge p in s may con ibu e o exis ing da abases and
be applied o u u e s udies o uby and sapphi e iden i ica-
ion and o he de e mina ion o aud. In addi ion, hey also
p o ide a simple and as e app oach o FTIR spec oscopy
analysis.
Da a a ailabili y. All da a de i ed om his esea ch a e p e-
sen ed in Figs. 1, 2, 3, and 4 and Tables 1, 2, and 3.
Au ho con ibu ions. MGV and EMCG concep ualised he
p ojec . Expe imen s, da a acquisi ion, and analyses we e ca ied
ou by ASdS, wi h he supe ision o LBG and ADM. The o igi-
nal d a o he pape was p epa ed by ASdS, and i was e ised by
MGV and LBG. Funding acquisi ion was done by MGV. All au ho s
discussed and in e p e ed he esul s.
Compe ing in e es s. The con ac au ho has decla ed ha none
o he au ho s has any compe ing in e es s.
Disclaime . Publishe ’s no e: Cope nicus Publica ions emains
neu al wi h ega d o ju isdic ional claims made in he ex , pub-
lished maps, ins i u ional a ilia ions, o any o he geog aphical ep-
esen a ion in his pape . While Cope nicus Publica ions makes e -
e y e o o include app op ia e place names, he inal esponsibili y
lies wi h he au ho s.
Acknowledgemen s. The au ho s acknowledge he Gemology
School o he Uni e si y o Ba celona. This esea ch has been sup-
po ed by he Gene ali a de Ca alunya (g an no. 2021 SGR 00262)
and E asmus+P COIMBRA01.
Re iew s a emen . This pape was edi ed by Giuseppe C uciani
and e iewed by wo anonymous e e ees.
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