Gemological Characteristics and Discoloration Mechanism of Color-Chang Pyrope-Spessartine Garnet

Xiaoxu Yan; Suwei Yue; Shiyu Chen

doi:10.3788/LOP202259.1333001

Laser & Optoelectronics Progress, Volume. 59, Issue 13, 1333001(2022)

Gemological Characteristics and Discoloration Mechanism of Color-Chang Pyrope-Spessartine Garnet

Xiaoxu Yan¹, Suwei Yue^1,2、*, and Shiyu Chen¹

Author Affiliations

¹School of Jewelry, Guangzhou City University of Technology, Guangzhou 510800, Guangdong , China

²Institute of Jewelry, Guangzhou City University of Technology, Guangzhou 510800, Guangdong , China

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Figures & Tables(9)

Fig. 1. Feature of color-change garnet samples

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Fig. 2. Mid-infrared absorption spectral characteristics of color-change garnets

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Fig. 3. UV-Vis absorption spectral characteristics of color-change garnet

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Fig. 4. PL spectral characteristics of color-change garnet sample Sps-1

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$Sps-Prp-Alm ternary phase diagram projection of color-change garnet. (a) Sample species; (b) refractive index$

Fig. 5. Sps-Prp-Alm ternary phase diagram projection of color-change garnet. (a) Sample species; (b) refractive index

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Table 1. Standard gemological characteristics of color-change garnets

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Table 1. Standard gemological characteristics of color-change garnets

Sample	Weight /g	Color		Fluorescence	Luster	Specific gravity	Refractance index^*
Sample	Weight /g	Daylight	Incandescent light	Fluorescence	Luster	Specific gravity	Refractance index^*
Sps-1	0.128	Cyan	Orange	Inert	Glassy	4.16	1.775
Sps-2	0.104	Cyan	Orange	Inert	Glassy	4.15	1.770
Sps-3	0.106	Cyan	Orange	Inert	Glassy	4.14	1.773

Table 2. Component of sample Sps-1 with EPMA

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Table 2. Component of sample Sps-1 with EPMA

Component	Percentage of mass /%			Relative molecular mass	State of ion	Amount of ion /mol
Component	Sps-1	Sps-2	Sps-3	Relative molecular mass	State of ion	Sps-1	Sps-2	Sps-3
SiO₂	39.327	36.684	37.552	60.08	Si⁴⁺	3.0709	2.8722	2.9512
TiO₂	0.033	0.067	0.080	79.90	Ti⁴⁺	0.0019	0.0040	0.0047
Al₂O₃	20.614	21.372	21.870	101.96	Al³⁺	1.8971	1.9721	2.0257
Cr₂O₃	0.222	0.240	0.211	151.99	Cr³⁺	0.0137	0.0149	0.0131
TFeO^a	2.455	2.118	2.441	71.84	Fe^3+b	0.0407	0.0956	0.0000
TFeO^a	2.455	2.118	2.441	71.84	Fe^2+b	0.1197	0.0431	0.1604
MnO	26.636	27.859	27.299	70.94	Mn²⁺	1.7617	1.8475	1.8172
MgO	7.421	9.112	7.269	40.30	Mg²⁺	0.8639	1.0636	0.8516
CaO	2.175	2.023	2.384	56.08	Ca²⁺	0.1820	0.1697	0.2007
Total	98.883	99.475	99.106
Fomula of sample Sps-1：（Mn_1.762Mg_0.864Ca_0.182Fe_0.120）_2.928（Al_1.897Fe_0.041Cr_0.014Ti_0.002）_1.954Si_3.071O₁₂
Fomula of sample Sps-2：（Mn_1.848Mg_1.064Ca_0.170Fe_0.043）_3.125（Al_1.972Fe_0.096Cr_0.015Ti_0.004）_2.087Si_2.872O₁₂
Fomula of sample Sps-3：（Mn_1.817Mg_0.852Ca_0.200Fe_0.160）_3.029（Al_2.026Cr_0.013Ti_0.005）_2.044Si_2.951O₁₂

Table 3. Mid-infrared absorption spectral characteristics and peak arrangement of color-change garnet

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Table 3. Mid-infrared absorption spectral characteristics and peak arrangement of color-change garnet

Absorption of color-change garnet samples /cm^-1			Arrangement of absorptions	Absorption of Ref.［15-17］/cm^-1
Sps-1	Sps-2	Sps-3	Arrangement of absorptions	Absorption of Ref.［15-17］/cm^-1
980（s）	982（s）	982（s）	ν_as（Si―O―Si）	964-980
899（m）	897（m）	897（m）		884-890
866（m）	866（m）	865（m）		860
638（w）	635（w）	635（w）	γ_as（Si―O―Si）	630-637
575（s）	577（s）	575（s）		556-570
527（sh）	527（sh）	527（sh）		521
486（s）	484（m）	486（m）		480
453（m）	453（m）	451（m）	δ（Al―O―Si）	451

Table 4. Mass fraction of each end member in color-change garnet samples
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Table 4. Mass fraction of each end member in color-change garnet samples
Sample RI Mass fraction /%
Uvt Adr Prp Sps Grs Alm Other Total
Sps-1 1.775 0.70 2.08 29.51 60.18 3.43 4.09 — 99.99
Sps-2 1.770 0.71 4.59 34.05 59.14 0.13 1.38 — 100.00
Sps-3 1.773 0.64 — 27.85 59.42 5.92 5.25 0.92 100.00

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Xiaoxu Yan, Suwei Yue, Shiyu Chen. Gemological Characteristics and Discoloration Mechanism of Color-Chang Pyrope-Spessartine Garnet[J]. Laser & Optoelectronics Progress, 2022, 59(13): 1333001

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