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Amethyst and morion quartz gemstone raw materials from Turkey: colorsaturation and enhancement by gamma, neutron and beta irradiationM. Hatipoğlua; C. Helvacıb; R. Kibarc; A. Çetinc; Y. Tuncerc; N. Canc

a Gemmology and Jewellery Program, Izmir Multidisciplinary Vocational School, Dokuz EylülUniversity, Izmir, Turkey b Department of Geology, Faculty of Engineering, Dokuz Eylül University,Izmir, Turkey c Department of Physics, Faculty of Arts and Science, Celal Bayar University, Muradiye,Manisa, Turkey

First published on: 23 June 2010

To cite this Article Hatipoğlu, M. , Helvacı, C. , Kibar, R. , Çetin, A. , Tuncer, Y. and Can, N.(2010) 'Amethyst and morionquartz gemstone raw materials from Turkey: color saturation and enhancement by gamma, neutron and betairradiation', Radiation Effects and Defects in Solids, 165: 11, 876 — 888, First published on: 23 June 2010 (iFirst)To link to this Article: DOI: 10.1080/10420150.2010.489611URL: http://dx.doi.org/10.1080/10420150.2010.489611

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Radiation Effects & Defects in Solids: Incorporating Plasma Science & Plasma Technology

Vol. 165, No. 11, November 2010, 876–888

Amethyst and morion quartz gemstone raw materials fromTurkey: color saturation and enhancement by gamma, neutron

and beta irradiation

M. Hatipoglua, C. Helvacıb, R. Kibarc, A. Çetinc, Y. Tuncerc and N. Canc*

aGemmology and Jewellery Program, Izmir Multidisciplinary Vocational School, Dokuz Eylül University,35160 Buca, Izmir, Turkey; bDepartment of Geology, Faculty of Engineering, Dokuz Eylül University,

35160 Buca, Izmir, Turkey; cDepartment of Physics, Faculty of Arts and Science, Celal Bayar University,45140 Muradiye, Manisa, Turkey

(Received 5 March 2010; final version received 25 April 2010 )

Color-enhancement investigations without using heating treatment from dull or pale to ideal saturationand/or changes to the formation of the rarer attractive colors are widely conducted to revalue abandoned gemmaterial sources in the world. Such an investigation is carried out on pale or dull purple-colored amethystand smoky-colored morion samples, which are two important gem species of the crystalline quartz (SiO2)mineral that are currently abandoned in natural deposits in Turkey because of their unattractive coloration.The results of color enhancements observed on these samples, after irradiation with artificial gamma,neutron and beta beams, were examined by comparing with samples with the ideal color saturation andalso with colorless samples, using optical absorption (OA) and radioluminescence (RL) spectroscopy. TheICP-AES analyses reveal that the main impurity elements of over 100 ppm in abundance in these quartzspecies are aluminum, iron and titanium for amethyst, and aluminum, iron, titanium and manganese formorion. The OA spectra indicate that vivid purple coloration of amethyst is due to the transmittance at about395–420 nm band gap as a result of absorbance peaks at 375, 480 and 530 nm. These absorbances may berelated to the unusual oxidized small proportions of certain impurity ions, after being exposed mainly togamma irradiation, such as Al(IV) from the total aluminum, Ti(V) from the total titanium and Fe(IV) fromthe total iron, respectively. However, the RL spectroscopy of amethyst samples before and after they wereexposed to artificial gamma, neutron and beta radiation beams demonstrates that the ions most affected byirradiation are Fe(IV) first and Al(IV) and Ti(V) second, and these ions represent the RL peaks at 600, 720and 495 nm, respectively. The OA spectra indicate that dark smoky coloration in morion is due to a lack oftransmittance at the visible region as a result of the absorbance peaks at 375, 450–490, 620 and 730 nm.These absorbances also may be related to the unusual oxidized small proportions of certain impurity ionsby irradiation, such as Al(IV) from the total aluminum, Ti(V) from the total titanium and Mn(III) from thetotal manganese, respectively. In addition, the buoyancies of these absorbance peaks in the visible regionproduce the color hues between light smoky and dark smoky colorations in morion samples. These oxidizedion states are more resistant and stable against environmental destructive conditions in comparison withamethyst. Thus, the dark smoky coloration of morion becomes dull or pale after relatively longer periods.But, the RL spectroscopy of morion before and after being exposed to gamma, neutron and beta irradiationbeams demonstrates that the most induced ions from the irradiation are Mn(III) and Al(IV) first and Ti(V)second. These ions represent the RL peaks at about 400, 720 and about 500 nm, respectively.

Keywords: natural gemmy amethyst and smoky (morion) quartz crystals; color saturation and enhance-ment; radiation beams; ICP-AES, OA; RL; Turkey

*Corresponding author. Email address: cannurdogan@yahoo.com

ISSN 1042-0150 print/ISSN 1029-4953 online© 2010 Taylor & FrancisDOI: 10.1080/10420150.2010.489611http://www.informaworld.com

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1. Introduction

Quartz (SiO2) crystals with some impurity elements substituting for Si4+ absorb energy fromionizing radiation and modify their color, producing the color centers (1, 2). The colorationmechanisms of amethyst and smoky quartz or dark smoky morion quartz (crystalline gem quartzspecies) have been already disputed and have been the subject of many investigations. The studieson the color origins of these quartz species have shown that some mechanic procedures take placeduring the coloring of the amethyst (3–6).

This study is focused on amethyst and smoky quartz species, which are the two most importantcrystalline silica gem materials of Turkey. However, vivid or saturated-colored gem roughs aremore precious than those of dull or pale-colored roughs. The vivid purple coloration of amethystand the smoky or dark smoky (morion variety) coloration of smoky quartz (7, 8) is desirable ingem markets worldwide (4). Nevertheless, large reserves of these rough materials found in naturalsources consist of mainly dull- or pale-colored samples. Thus, they have been mostly abandonedas useless roughs, as is the case in Turkey.

It has been proved experimentally via synthetic productions of both amethyst and smokyquartz species that color formations in both crystalline silica species are due to the color cen-ters that are produced as a result of exposure mainly to gamma irradiation of some substitutedimpurity elements (mainly iron and aluminum) in the SiO4 tetrahedral in the quartz lattice(1, 9–11). The main scope of this study is the experimental investigation of whether or not artifi-cial irradiation inducements are an alternative technique to the traditional heating inducement forcolor enhancement for ideal color saturation and/or color change for producing rare colorationsof dull or pale-colored abandoned gem materials from natural sources. According to this, first,the impure elements producing the color centers in amethyst and smoky (morion) quartz samplesfrom Turkey are precisely established by chemical analyses (XRF and ICP-AES). Second, thecolor enhancements to vivid purple and dark smoky (morion) and/or color changes to yellow dis-playing in spectroscopic graphics (OA and RL) are compared with each other and with colorlessquartz samples of both natural and synthetic origin. In the mean time, the inducement relationsbetween impure ions substituting for Si4+ in the silica lattice and irradiation will be revealed.

2. Materials and experimental procedure

Samples of natural amethyst from the Dursunbey-Balıkesir region and smoky quartz from Koçarlı-Aydın region were chosen because of both the excellent saturated and dull or pale colors they canenhance (Figures 1 and 2). Initial gamma-irradiated amethyst crystals in the region are filled intothe post-volcanic tension fractures with NW–SE direction formed during the Early Miocene Period(about 18–23.8 Myr), cutting the andesitic–dasitic volcanic surrounding rocks (12, 13). Initialgamma-irradiated smoky quartz crystals in the region are filled into the post-metamorphic tensionfractures with E–W direction formed during the Late Oligocene Period (about 23.8–28 Myr),cutting the schist and gneiss metamorphic basement rocks (14).

In addition, in order to compare natural colorless quartz samples from the Çine-Aydın regionand synthetic-produced Lumbered Y-bar-type colorless quartz, samples from Sawyer ResearchProducts, Inc., Eastlake, OH, USA, were obtained. Slices of 10 × 10 × 1 mm3 were cut fromthese samples with the square faces perpendicular and parallel to the ‘c’ crystal axis. Both sidesof the slices with various thicknesses were mechanically polished with four different diamondpastes from 200 to 3000 mesh.

To determine the impurity elements of the amethyst and morion quartz samples, the XRF formajor oxides, ICP-AES for trace elements and WST-SIM for loss of igneous techniques (Table 1)by the accredited ALS Chemex Laboratory, Canada, were performed.

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Figure 1. Amethyst samples found in natural sources in Turkey. Vivid and pale purple-colored samples with a maximumcrystalline teeth size of 5 cm (a). Pale purple-colored sample with a maximum crystalline teeth size of 1 cm (b). Vividpurple-colored sample with a maximum crystalline teeth size of 5 cm (c). Natural location (Dursunbey-Balıkesir region) inTurkey (d). Initial gamma-irradiated amethyst crystals in the region are filled into the post-volcanic tension fractures withNW–SE direction formed during the Early Miocene Period (about 18–23.8 Myr), cutting the andesitic–dasitic volcanicsurrounding rocks (12, 13), (e) and (f).

Optical absorption (OA) spectra of both the natural and artificially irradiated samples weretaken using Varian DMS 90 UV/VIS and Sosco Model 7800 UV/VIS spectrophotometers in therange of 200–800 nm.

Dull or pale-colored amethyst and morion samples were irradiated with gamma, neutron andbeta beams. The temperature in the irradiation room was in the range of 15–35◦C. For gamma (γ )irradiation, a Gammacell-220 dry gamma irradiator device was used. Its radioactive material is60Co. Its radiation energy is 12.400 Ci and I = 0.08 Mrad. The samples were irradiated for 24 and43 h. For neutron irradiation, a Siemens device was used. The samples were irradiated by 3 MeVneutrons with two different neutron fluxes. After 2 h 20 min, 15.15 × 107 n/cm2 were counted in

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Figure 2. Smoky quartz samples found in natural sources in Turkey. Dark smoky-colored morion quartz samples of amaximum 20 cm in size (a). Pale smoky-colored quartz samples of a maximum 4 cm in size (b). Smoky-colored quartzsample of 8 cm in size (c). Natural location (Koçarlı-Aydın region) in Turkey (d). Initial gamma-irradiated smoky quartzcrystals in the region are filled into the post-metamorphic tension fractures with the E–W direction formed during theLate Oligocene Period (about 23.8–28 Myr), cutting the schist and gneiss metamorphic basement rocks (14) (e). Displayof the samples by local miner (f).

the monitor for the first group. After 2 h 50 min, 20.42 × 107 n/cm2 were counted in the monitorfor the second group. For beta (β) irradiation, a Siemens Betatron-500A device was used and thesamples were irradiated for 10 min in a 7 MeV electron each at 800 pulses to 2.000 rad and 1600pulses to 4.000 rad.

For radioluminescence (RL) measurements of the natural and irradiated samples, a JobinYvonspectrophotometer coupled with a CCD detector was used. X-ray irradiation was supplied via atungsten X-ray tube (Machlett OEG-50A) with a current setting of 15 mA and a voltage of 30 kV,delivering a dose rate of 10 Gy/min to the samples. Signals were recorded over the wavelengthrange of 200–800 nm.

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Table 1. Chemical bulk and trace element analyses of the natural amethyst and smoky quartz samples from Turkey.

Samples Samples

Oxides % Instrument Amethyst Smoky quartz Elements Instrument Amethyst Smoky quartz

SiO2 XRF 97.92 98.45Al2O3 XRF 0.17 0.12 Al ICP-AES 0.12% 0.09%Fe2O3 XRF 1.48 1.17 Fe ICP-AES 1.08% 0.84%TiO2 XRF <0.01 0.02 Ti ICP-AES <0.01% <0.01%MnO XRF 0.01 0.08 Mn ICP-AES 71 ppm 554 ppmCr2O3 XRF 0.01 <0.01 Cr ICP-AES 8 ppm 5 ppmNa2O XRF 0.05 0.02 Na ICP-AES 0.02% 0.01%K2O XRF 0.03 0.03 K ICP-AES 0.02% 0.02%CaO XRF 0.07 0.06 Ca ICP-AES 0.03% 0.04%MgO XRF 0.09 0.08 Mg ICP-AES 0.01% 0.01%SrO XRF <0.01 0.01 Sr ICP-AES 2.5 ppm 4 ppmBaO XRF <0.01 <0.01 Ba ICP-AES 34.4 ppm 30 ppmP2O5 XRF <0.01 0.014 P ICP-AES 6 ppm 30 ppmLOI XRF 0.2 −0.08 Ag ICP-AES 0.5 ppm <0.5 ppmTotal XRF 100.04 99.98 As ICP-AES 2.2 ppm 6 ppm

Be ICP-AES 2 ppm <0.5 ppmBi ICP-AES <0.1 ppm <0.2 ppmCd ICP-AES 0.4 ppm <0.5 ppmCo ICP-AES 2.8 ppm 1 ppmCu ICP-AES 10.6 ppm 5 ppmGa ICP-AES 9.8 ppm <10 ppmLa ICP-AES 0.1 ppm <10 ppmMo ICP-AES 6.1 ppm 1 ppmNi ICP-AES 19.9 ppm 4 ppmPb ICP-AES 32.1 ppm 3 ppmS ICP-AES <0.02% 0.02%

Sb ICP-AES 3.3 ppm <5 ppmSc ICP-AES 1 ppm <1 ppmTh ICP-AES <0.1 ppm <20 ppmTa ICP-AES <10 ppm <10 ppmU ICP-AES <0.1 ppm <10 ppmV ICP-AES 11 ppm 3 ppmW ICP-AES 0.4 ppm <10 ppmZn ICP-AES 66 ppm 8 ppm

Notes: Al, Fe and Ti elements in the amethyst sample and Al, Fe, Ti and Mn elements in the smoky quartz sample substituting for the Sielement in a silica lattice are remarkable as ≥100 ppm. Because the irradiation beams in fact affect all these impurity elements: they areresponsible for the producing of the color centers directly and indirectly.

3. Results and discussion

Two important colored gem species of the crystalline quartz (SiO2) minerals, amethyst and morion,are investigated to reveal whether or not both color enhancement for producing vivid colorationand color changes to produce rare colors occurs, such as citrine enhancement by artificial radiationbeams such as gamma, neutron and beta.

Chemical bulk and trace element analyses (Table 1) of the natural amethyst and smoky quartzsamples from Turkey demonstrate that the Al, Fe, Ti elements in the amethyst samples and Al,Fe, Ti and Mn elements in the smoky quartz samples substituting for Si element in the silicalattice are remarkable as ≥100 ppm. In the previous studies based on the synthetic produc-tions of both amethyst and smoky quartz, it is proved that certain impurity elements producethe color centers (2, 10). However, the kinds and oxidization states of the impurity elementshave already divided researchers. Al and Fe elements are the most accepted and investigatedimpurity elements (5, 15–19). Some researchers have stated that H and OH play an impor-tant role in some quartz species (20–23). As seen, the role of other impurity elements should

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have been kept away from the sight of producing color centers. This study comparatively inves-tigated amethyst and morion crystalline quartz species from Turkey and found that the Ti inamethyst and Ti and Mn in morion may play important roles in producing color centers in thesespecies. The existence of Ti in Turkish amethyst seems to be slightly different from Brazilianamethyst (24, 25). This differential situation may be attributed to different geological formationsand depositions.

On the other hand, we know well that the production of the color centers of these impurityelements without being irradiated is impossible. Thus, the quartz crystal samples including someimpurity elements absorb energy from the ionizing radiation and modify their color by producingthe color centers. The most effective irradiation is gamma beams for both amethyst and smokyquartz species (2, 11, 26). The main outstanding problem is the inducement gradations and newoxidation ion states of these impurity elements after being exposed mainly to gamma irradiation.In particular, the existence of unusual oxidized Fe(IV) in amethyst samples has been stated inmany papers (10, 11, 17, 27, 28). We have concluded that all impurity elements were induced byirradiation and were oxidized to unusual ion stages even if small amounts were present.

As seen in the OA spectra of both amethyst and morion samples (Figures 3–5), the vividpurple coloration of amethyst is due to the transmittance of light rays at about 395–420 nm afterabsorbances of light rays at 375 nm in the UV region and 480 and 530 nm in the visible region.This transmitting area represents ‘H’ and ‘K’ as Fraunhofer lines (3, 29). However, the darksmoky coloration of morion is due to a lack of transmittance of light rays in the visible regionafter absorbances of light rays at 375 nm in the UV region, 450–490 and 600–640 nm in the

Figure 3. OA spectra of natural gem quality of vivid purple amethyst and dark smoky (morion) quartz samples fromTurkey, compared with the natural gem quality colorless quartz sample from Turkey and the synthetic LumberedY-bar-typecolorless quartz sample from Sawyer Research Product, Inc., Eastlake, OH, USA.

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Figure 4. OA spectra of natural purple amethyst sample with vivid color saturation and of initially pale purple-coloredamethyst samples after they were exposed to artificial gamma, neutron and beta irradiations. Vivid purple coloration ofthe amethyst is due to the transmittance of light rays at about 390–420 nm after absorbances of light rays at 375 nm in theUV region and 480 and 530 nm in the visible region. This transmittance area represents ‘H’ and ‘K’ as Fraunhofer lines.

visible region and 730 nm in the IR region. Because of the lack of any transmittance in the visibleregion, the transmitting area does not represent as Fraunhofer lines. These absorption peaks maybe related to the oxidized ion stages of impurity elements. This correlation is given in Table 2

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Figure 5. OA spectra of natural dark brown smoky quartz sample with vivid color saturation and of initially palebrown-colored smoky quartz samples after they were exposed to artificial gamma, neutron and beta irradiations. Darkbrown-blackish coloration of smoky quartz is due to the lack of transmittance of light rays in the visible region afterabsorbance of light rays at 375 nm in the UV region, 450–490 and 600–640 nm in the visible region and 730 nm in theIR region. Because of the lack of any transmittance in the visible region, the transmittance area does not represent asFraunhofer lines.

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Table 2. Correlation between main impurity elements producing color centers (≥100 ppm) and spectroscopic peaks ofoptical absorption and radioluminescence spectra.

Samples with gamma-induced color centers

Amethyst Smoky quartz

Impurity ions and Optical Radioluminescence Optical Radioluminescenceoxidized states absorption (nm) (nm) absorption (nm) (nm)

Al(IV) 375 720 375 720Ti(V) 480 495–510 450–490 495–510Fe(IV) 530 600 – –Fe(II) or Fe(III) – – 620 –Mn(III) – 385–410 730 385–410

Notes: It is noted that the Fe(II) ion, which is more abundant than the Fe(III) ion in the smoky quartz sample, is relatively resistant toirradiation beams. Thus, the RL spectra do not display a remarkable peak.

for Turkish amethyst and morion species. It is well known that the main absorption peak at about530 nm in the OA spectra of the amethyst species is related to the Fe(IV) ion (10, 11, 27, 28),though this peak was related to Fe(III) by some researchers (16, 19).

OA graphics (Figures 4 and 5) of initially dull or pale purple-colored amethyst and smoky-colored quartz samples, after they were exposed to artificial gamma, neutron and beta irradiationdepending on the various doses and periods, demonstrate that only gamma irradiation affects thecolor enhancement of the ‘useless’gem roughs. On the other hand, these artificial radiation induce-ments do not cause any color changes to produce rare silica species, such as citrine or ametrine(10–30). Color enhancement and changing results are revealed according to the Color HarmonyManual (31). This situation demonstrates that the residue impurity elements, except their initialoxidized proportions, are not induced, except a small amount by any irradiation in a short period.

To reveal which impurity elements were induced from the radiation beams, the RL graphics(Figures 6 and 7) of the same samples are taken and irradiated with both natural and artificialgamma, neutron and beta beams. The RL spectroscopy results are given in Table 1 and related tothe oxidized impurity ions. Ultimately, it is fact that the Fe(II) ion from the total iron, which is moreabundant in morion crystals than in amethyst crystals, based on the optical spectrum, is relativelyresistant to irradiation even if the ion is partially oxidized to Fe(III) ion by irradiation. Whilefinding these relationships, we first considered a comparison with the RL graphics (Figure 8)of both natural and synthetic quartz samples. We have concluded that the RL peak at 720 nmcertainly represents the oxidized Al(IV) ion. In conclusion, we can say that this RL study is moredistinctive than other luminescence data to detect the locations of the induced impurity elementswhen compared with previous studies (9, 21, 23, 32).

Ultimately, when we evaluate together the simplified RL graphics (Figure 9) of all colored andcolorless samples after artificial gamma radiation inducements, we can see the locations of thesame and different, unusual oxidized impurity ions.

4. Conclusions

OA and RL spectroscopy were performed and analysed on optically polarized amethyst andmorion quartz crystal samples obtained from deposits in Turkey, before and after irradiation withartificial gamma, neutron and beta rays at several energy doses and times. In addition, the resultswere compared with those of natural and synthetic colorless quartz crystal samples. As notedhere, both OA and RL spectra of the amethyst and morion gem quartz species from Turkey areslightly different.

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Figure 6. RL spectra of natural purple amethyst sample with vivid color saturation and of initially pale purple-coloredamethyst samples after they were exposed to artificial gamma, neutron and beta irradiation.

As a result, this study sheds light on the color saturation and changing enhancements by artificialirradiation (gamma, neutron and beta) for dull-colored silica gem materials such as amethyst andmorion. Both the vivid purple color formation of the amethyst samples and the dark smoky colorformation of the morion samples are due to the unusual oxidized ion states in small proportions

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Figure 7. RL spectra of the natural dark smoky (morion) quartz sample and of initially pale smoky-colored quartzsamples after they were exposed to artificial gamma, neutron and beta irradiation. It is accepted that the Fe(II) ion, whichis more abundant than the Fe(III) ion in the smoky quartz samples, is relatively resistant to irradiation beams.

of the certain impurity elements substituting for Si4+ ion in the SiO4 tetrahedral, after they wereexposed mainly to gamma irradiation. During this process, a few of impurity elements wereoxidized to the unusual ion states, such as Al(IV) from Al(III), Fe(IV) from Fe(III), Ti(V) from

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Figure 8. RL spectra of natural and synthetic colorless quartz samples after they were exposed to artificial gammaradiation beams. Collective RL peak is at 720 nm. This represents the most affected impurity ion [Al(IV)] from theradiation inducement. The distinctive RL peak at 390 nm may be attributed to the existence of a residue impurity ion[Mn(III)] affected from the radiation inducement in natural colorless quartz sample.

Figure 9. Collective display of the reaction bands and their peaks in the simplified RL graphics of the most affectedimpurity ions from the radiation inducement, after the artificial gamma irradiation beam of natural pale-colored amethystand smoky quartz samples, and also the natural and synthetic colorless quartz samples.

Ti(IV) and Mn(III) from Mn(II). Thus, these produce the unstable color centers in crystallinequartz lattice. Nevertheless, the oxidized ion states are no longer stable when exposed to artificialdestructive heating, such as firing and/or lighting, such as sunshine. As a result of these destructiveconditions on both amethyst and morion, with a reversible process, the unstable oxidized ionswere reduced to a stable oxidation state, thus becoming colorless or pale-colored again.

In addition, the coexistence of huge diversities from purple to violet in amethyst and fromlight smoky to dark smoky in morion in the same deposit is due to the broadening or shiftingof the main OA bands of these species depending on the irradiation dose. The more the unusual

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oxidized proportions from total amounts of the certain impurity elements, the better the vivid ordark coloration.

Both color enhancement for producing vivid coloration and color changes to produce rare colors,such as citrine, reveal that dull or pale-colored amethyst and morion crystals may be enhanced byartificial gamma irradiation only to produce vivid purple and dark smoky colorations. Neutron andbeta are not suitable irradiation sources for this purpose. Therefore, many raw amethyst and smokyquartz samples from natural sources which have been abandoned in Turkey and worldwide becauseof their unattractive coloration may be revalued and become economically useful by carrying outthe artificial gamma irradiation method, as well as cutting and polishing the gem objects.

In addition, it is revealed that the artificial gamma, neutron and beta irradiation could notcreate different colorations in the amethyst and smoky quartz species. Therefore, the irradiationmethod cannot be an alternative method for color changing instead of the traditional heatingtreatment method.

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