Optical Spectra of Spinel, MgAl₂O₄       (gahnite below)

• Conrin F (1934): Spectre d'absorption de la viri dine. Bulletin de la Société belge de géologie, de paléontologie et d'hydrologie 44, 313-315.

• Grum-Grzhimailo SV (1958) The color of idiochromatic minerals. Zapiski Vserossiiskogo Mineralogicheskogo Obshchestva 87, 129-50. (in Russian) 

• Slack GA, Ham FS, Chrenko RM (1966) Optical absorption spectra of tetrahedral Fe²⁺ (3d⁶) in cubic ZnS, CdTe and MgAl₂O₄. Physical Review 152, 376-402. 
• Wood DL, Imbusch GF, MacFarlane RM, Kisliuk P, Larkin PM (1968) Optical spectrum of Cr³⁺ in spinels. Journal of Chemical Physics 48, 5255-5262.
  
• Ferguson J, Wood dL, van Uitert LG (1969) Crystal-field spectra of d^3,7 ions. V. Tetrahedral Co²⁺ in ZnAl₂O₄ spinel. Journal of Chemical Physics 51, 2904-4909.
• Reed KS. Lau HF (1969) Optical Spectra of 3d Transition Metal Ions in MgO·Al₂O₃ - MgO·3.5Al₂O₃ Spinel. Journal of The American Ceramic Society 52, 307-311.
• Sakurai T, Ishigame M, Arashi H (1969) Absorption spectrum of Ni²⁺ ions in spinel. Journal of Chemical Physics 50, 3241-3245.    

• Boksha ON, Grum-Grzhimailo SV, Popova AA, Sviridov DT, Smirnova EF (1970) Optical spectra of spinels. Grum-Grzhimailo SV, editor. Spektrosk Krist, Mater. Simp. 2d , 302-308.
• Reed JS (1971) Optical absorption spectra of Cr³⁺ in MgO·Al₂O₃ - MgO·3.5Al₂O₃ spinels. Journal of The American Ceramic Society 54, 202-204.
• Boksha ON, Varina TM, Popova AA (1972) Optical-spectra of Cr and Mn in synthetic spinels MgO-Al₂O₃. Kristallografiya 27, 1063- (in Russian).
• Gaffney ES (1973) Spectra of tetrahedral Fe²⁺ in MgAl₂O₄. Physics Review B8, 3484-3486.
• Sviridov DT, Sevastyanow BK, Orekhova VP, Sviridova RK, Veremeichik TF (1973) Optical absorption spectra of excited Cr3+ ions in magnesium spinel at room and liquid nitrogen temperatures. Opt Spect 35, 59-61.
• Mao HK, Bell PM (1974) Crystal-field effects in spinel: oxidation states of iron and chromium. Carnegie Inst. Washington Yearbook 73, 332-341
• Shankland TJ, Duba AG, Woronow A (1974) Pressure shifts of optical absorption bands in iron-bearing garnet, spinel, olivine, pyroxene and periclase. Journal of GeoPhysical Research 79, 3273-3282. 
• Mao HK, Bell PM (1975) Crystal-field effects in spinel: oxidation states of iron and chromium. Geochim Cosmochim Acta 39, 865-874
• Dickson BL, Smith G (1976) Low temperature optical absorption and Mössbauer spectra of staurolite and spinel. Canadian Mineralogist 14, 206-215.
• Mao HK (1976) Charge-transfer processes at high pressure. In: The Physics and Chemistry of Minerals and Rocks. RGJ Strens, ed., J Wiley, New York, p. 573-581
• Bukanov VV, Platonov AN, Taran MN (1977) Colour of gem quality spinels from Kuhilal deposit. Zapiski Vsesoyuznogo Mineralogicheskogo Obshchestva 5,  565-571 (in Russian).
• Yagi T, Mao HK (1977) Crystal-field spectra of the spinel polymorph of Ni₂SiO₄ at high pressure. Carnegie Institute of Washington Yearbook 17, 505-508
• Burns RG, Sung CM (1978) The effect of crystal field stabilization on the olivine - spinel transition in the system Mg₂SiO₄ - Fe₂SiO₄. Physics and Chemistry of Minerals 2, 349-364

• Schmetzer K, Gübelin E (1980) Alexandrite-like spinel from Sri Lanka. Neues Jahrbuch für Mineralogie Mh 1980, 428-432.
• Schmetzer K (1982) Absorptionsspektroskopie und Farbe vokn V³⁺-haltigen natūrlichen Oxiden und Silikaten - ein Beitrag zur Kristallchemie des Vanadiuiims. N Jb Mineral Abhandlungen 144, 73-106.
  
• Shigley JE, Stockton CM (1984) Cobalt-blue gem spinels. Gems & Gemology 20, 34-41.
• Harding RR, Wall F (1987) Blue spinel from the Hunza valley, Pakistan. Journal of Gemmology 29, 403-405.
• Taran MN, Platonov AN, Pol'shin EV, Matsyuk SS (1987) Optical spectra and coloration of natural spinels of the (Mg,Zn,Fe)(Al,Fe)₂O₄ composition. Mineralogicheskiy Zhurnal 9, 3-15 (in Russian)
• Matsyuk, SS, Platonov AN, Polshin EV, Taran MN, Tatarintsev VI, Badion NS, Vishnevski AA, Safronov AF, Smirnov GI  (1989) Spinels of Mantle Rocks. Pavliship VI, editor. Academy of Sciences of the Ukrainian SSR. Kiev: Science Dumka 1989. 212 pages.
• Schmetzer K, Haxel C, Amthauer G (1989) Colour of natural spinels, gahnospinels and gahnites. Neues Jahrbuch für Mineralogie. Abhandlungen 160, 159‒180.
• Taran MN, Bondar YuH, Matsyuk SS, Polshin EV (1989) Spectroscopic investigations of olivine and chromite from the Marjalachti meteorite. Mineralogicheskiy Zhurnal 11,  80-87 (in Russian)

• Taran MN, Matsuk SS, Bondar YV (1991) Optical spectra and composition of olivine and spinel from the Marialakhti and Eagle Station pallasites. Geochem International 28, 110-118; Translated from Geokhimiya 4, 573-582.
• Czaja M, Mazurak Z (1993) Vibrational structure of luminiscence spectrum of Cr³⁺ in MgAl₂O₄. Physics and Chemistry of Minerals 20, 120-122.
• Taran MN, Langer K, Platonov AN, Indutny VV (1994) Optical absorption investigation of Cr³⁺ ion-bearing minerals in the temperature range 77-797 K. Physics and Chemistry of Minerals 21, 360-372.
• Langer K, Taran MN, Platonov AN (1997) Compression modui of Cr³⁺-centered octahedra in a variety of oxygen-based rock-forming minerals. Physics and Chemistry of Minerals 24, 109-114.

• Andreozzi GB. Hålenius U, Skogby H (2001) Spectroscopic active ^IVFe³⁺-^VIFe³⁺ clusters in spinel-magnesioferrite solid solution crystals: a potential monitor for ordering in oxide spinels. Physics and Chemistry of Minerals 28, 435-444.
• Rossman GR, Taran MN (2001) Spectroscopic standards for four- and five-coordinated Fe²⁺ in oxygen-based minerals.  American Mineralogist 86, 896-903
• Hålenius U, Skogby H, Andreozzi GB (2002) Influence of cation distribution on the optical absorption spectra of Fe³⁺-bearing spinel s.s.–hercynite crystals: evidence for electron transitions in ^VIFe²⁺–^VIFe³⁺ clusters. Physics and Chemistry of Minerals 29, 319-330.
• Skogby H, Hålenius U (2003) An FTIR study of tetrahedrally coordinated ferrous iron in the spinel-hercynite solid solution. American Mineralogist 88, 489-492.
• Andreozzi GB, Baldi G, Bernardini GP, Benedetto GD, Romanelli M (2004) ⁵⁷Fe Mössbauer and electronic spectroscopy study on a new synthetic hercynite-based pigment. Journal of the European Ceramic Society 24, 821–824.
• Lenaz D, Skogby H, Princivalle F, Hålenius U (2004) Structural changes and valence distribution in the MgCr₂O₄-FeCr₂O₄ solid solution series. Physics and Chemistry of Minerals 31, 633-642. 
• Ikeda K, Nakamura Y, Masumoto K, Shima H (2005) Optical Spectra of Synthetic Spinels in the System MgAl₂O₄–MgCr₂O₄. Journal of the American Ceramic Society 80, 2672-2676.
• Reddy BJ, Frost RL (2005) Spectroscopic characterization of chromite from the Moa-Baracoa Ophiolitic Massif, Cuba. Spectrochimica Acta Part A 61, 1721–1728.
• Taran MN, Koch-Mūller M, Langer K (2005) Electronic absorption spectroscopy of natural (Fe²⁺, Fe³⁺)-bearing spinels of spinel s.s.-hercynite and gahnite-hercynite solid solutions at different temperatures and high-pressures. Physics and Chemistry of Minerals 32, 175-188.
• Jouini A, Sato H, Yoshikawa A, Fukuda T, Boulon G, Kato K, Hanamura E (2006) Crystal growth and optical absorption of pure and Ti, Mn-doped MgAl₂Os spinel. Journal of Crystal Growth 287, 313-317.
• Lenaz D, Skogby H, Princivalle F, Hålenius U (2006) The MgCr₂O₄-FeCr₂O₄ solid solution series: Effects of octahedral Fe³⁺ on T-O bond lengths. Physics and Chemistry of Minerals 33, 465-474.
• Bosi F, Hålenius U, Andreozzi, GB, Skogby H, Lucchesi S (2007) Structural refinement of Mn-doped spinel: a case for tetrahedrally coordinated Mn³⁺ in an oxygen-based structure. American Mineralogist 92, 27-33.
• Hålenius U, Bosi F, Skogby H (2007) Galaxite, MnAl₂O₄, a spectroscopic standard for tetrahedrally coordinated Mn²⁺ in oxygen-based mineral structures. American Mineralogist 92, 1225-1231.
• García-Lastra JM, Barriuso MT, Aramburu JA, Moreno M (2008) Microscopic origin of the different colors displayed by MgAl₂O₄:Cr³⁺ and emerald. Physical Review B 78, 085117.
• Taran MN, Koch-Müller M, Feenstra A (2009) Optical spectroscopic study of tetrahedrally coordinated Co²⁺ in natural spinel and staurolite at different temperatures and pressures. American Mineralogist 94, 1647-1652.

• Hålenius U, Andreozzi, GB, Skogby H (2010) Structural relaxation around Cr³⁺ and the red-green color change in the spinel (sensu stricto)-magnesiochromite (MgAl₂O₄-MgCr₂O₄) and gahnite-zincochromite (ZnAl₂O₄-ZnCr₂O₂) solid-solution series. American Mineralogist 95, 456–462.
• Malsy A, Klemm L (2010) Distinction of Gem Spinels from the Himalayan Mountain Belt. Chimia 64 (2010) 741–746
• Bosi F, Hålenius U, D'Ippolito V, Andreozzi GB (2012)  Blue spinel crystals in the MgAl₂O₄-CoAl₂O₄ series: Part II. Cation ordering over short-range and long-range scales. American Mineralogist 97, 1834–1840.
• Malasy AK, Karampelas S, Schwarz D, Klemm L, Armbruster T, Taun DA (2012) Orangey-red to orangey-pink gem spinels from a new deposit at Lang Chap (Tan Huong-Truc Lau), Vietnam. Journal of Gemmology 37, 19-27.
• Fregola RA, Skogby H, Bosi F, D’Ippolito V, Andreozzi GB, Hålenius U (2014) Optical absorption spectroscopy study of the causes for color variations in natural Fe−bearing gahnite: Insights from iron valency and site distribution data. American Mineralogist, 99, 2187−2195.
• Taran MN, Parisi F, Lenaz D, Vishnevskyy AA (2014) Synthetic and natural chromium-bearing spinels: an optical spectroscopy study. Physics and Chemistry of Minerals 41, 593-602.
• D’Ippolito V, Andreozzi GB, Hålenius U, Skogby H, Hametner K, Günther D (2015) Color mechanisms in spinel: cobalt and iron interplay for the blue color. Physics and Chemistry of Minerals 42, 431–439.
• Verger L, Darguad O, Rousse G, Rozsalyi E, Juhin A, Cabaret D, Cotte M, Glatzel P, Cormier L (2016) Spectroscopic properties of Cr³⁺ in the spinel solid solution ZnAl_2−xCr_xO₄. Physics and Chemistry of Minerals 43, 33-42.
• Promwongnan S, Ounorn P, Maneekrajangsaeng M, Leelawatanasuk T (2017) An unusual blue synthetic star spinel. The Journal of Gemmology 35, 500-502.
• Palke AC, Sun Z (2018). What Is Cobalt Spinel? Unraveling the Causes of Color in Blue Spinels. Gems & Gemology 54, 262.
  
• Andreozzi GB, D'Ippolito V, Skogby H, Hålenius U, Bosi F (2019) Color mechanisms in spinel: a multi-analytical investigation of natural crystals with a wide range of coloration. Physics and Chemistry of Minerals 46, 343–360. 
• Zoyza G, Lomthong P, Schwarz D, Yanyu C, Kleismantas A (2019) Spinels From Sri Lanka. 36th International Gemmological Conference IGC, August 2019, Nantes, France, p67-70. 

• Buathong A, Narudessombat N (2020) A Rare Bicoloured Spinel. The Journal of Gemmology 37, 250-251.
• Chankhantha C, Amphon R, Rehman HU, Shen AH (2020) Characterisationof Pnk-to-Red Spinel from Four Important Localities. The Journal of Gemmology 37, 393-403.
• Kruzslicz ÁB, Nasdala L, Wildner M, Škoda R, Redhammer GJ, Hauzenberger C, Wantanachaisaeng B (2020) Black spinel - a gem material from Bo Ploi, Thailand. The Journal of Gemmology 37, 66-79.
• Belley PM, Palke AC (2021) Purple gem spinel from Vietnam and Afghanistan: Comparison of trace element chemistry, cause of color, and inclusions. Gems & Gemology 57, 228-238.
• Soonthorntantkiul W, Weeramongkhonlert V, Palke A (2021) Spectroscopic characteristics of low-temperature heated blue to violet spinel. Gems & Gemology 57, 288-290..
• Williams C, Williams B, Laurs BM (2021) Grey Spinel from Ocua, Mozambique. The Journal of Gemmology 37, 772-774.
• Chankhantha C, Kitkhunthod P, Amphon R, Rehman HU, Shen AH (2022) Spectroscopic Characteristics and Causes of Colour Modification in Heat-Treated Pink-to-Red Spinel from Luc Yen, Vietnam.The Journal of Gemmology 38, 348-362
  
• Liu Y, Qi L, Schwarz D, Zhou Z (2022) Color mechanism and Spectroscopic Thermal Variation of Pink Spinel Reportedly from Kuh-I-Lai, Tajikistan. Gems & Gemology 58, 338-353.
• Pluthametwisute T, Wanthanachaisaeng B, Saiyasombat C, Sutthirat C (2022) Minor Elements and Color Causing Role in Spinel: Multi-analytical Approaches. Minerals 2022, 12, 928. https://doi.org/10.3390/min12080928
• Schwarz D, Liu Y, Zhou Z, Lomthong P, Rozet T (2022) Spinel from the Pamir Mountains in Tajikistan. The Journal of Gemmology 38, 138-154.
• Sun X, Gao Y, Zhao H (2022) Interesting Inclusions in a Purple Spinel from Tanzania. The Jourmal of Gemmology 38, 315-316.
• Wang ZM, Mao XT, Yin ZW, Chen C, Cheng TJ (2022) Study on the Spectral Characteristics and the Color-Change Effect of Spinel. Spectroscopy and Spectral Analysis 42, p3541.
• Williams C, Williams B (2022) Violet Spinel with Stong Green Fluorescence. The Jourmal of Gemmology 38, 219-221.
• Zhao L, Li G, Weng L (2022) Gemological snd Spectroscopic Characteristics of "Jedi" Spinel from Man Sin, Myanmar. Minerals 12, 1359.
• Jollands M, Ludlam A, Palke A, Vertriest W, Jin S, Cevallos P, Arden S, Myagkaya E, D'Haenens-Johannson U, Weeramongkhonlert V, Sun Z (2023) Color Modification of Spinel by Nickel (Ni) Diffusion: A New Treatment in the Gem Market. Gems & Gemology https://www.gia.edu/gia-news-research/nickel-diffused-spinel
• Krzemnicki, MS, Leuenberger A, Balmer W (2023) Cobalt-bearing Blue Spinel from Lukande, near Mahenge, Tanzania. The Journal of Gemmology 38, 474-493.
• Wu J, Sun X, Ma H, Ning P, Tang N, Ding T, Li H, Zhang T, Na Y (2023) Purple-violet gem spinel from Tanzania and Myanmar: Inclusion, spectroscopy, chemistry, and color. Minerals 13, 226.  https://doi.org/10.3390/min13020226.
  
• Wu J, Ma H, Li H (2023) Forsterite in a purple Tanzanian spinel. Gems & Gemology 59, 150-153.
• Bellley PM, Schollenbruch K, Groat LA, Wilson BS (2024) Cobalt-Blue Spinel from Baffin Island, Canada: Comparison to Other Mg-Al Spinels and a Chemical Discrimination Approach for the Colouration of Spinel. The Journal of Gemmology 39, 220-240.
• Xu  Q, Xu  B, Gao Y, Li S (2024) Characterization of Red, Pink, Orange, and Purple Gem-Quality Spinel from Four Important Areas.   Crystals 2024, 14, 50; https://doi.org/10.3390/cryst14010050  
  

Optical Spectra of Gahnite, ZnAl₂O₄

• Schmetzer K, Haxel C, Amthauer G (1989) Color of natural spinels, gahnospinels and gahnites. N Jb Mineral Abh 160, 159-180 

• Taran MN, Koch-Mūller M, Langer K (2005) Electronic absorption spectroscopy of natural (Fe²⁺, Fe³⁺)-bearing spinels of spinel s.s.-hercynite and gahnite-hercynite solid solutions at different temperatures and high-pressures. Physics and Chemistry of Minerals 32, 175-188.

• Lorenzi G, Baldi G, Di Benedetto F, Faso V, Lattanzi P, Romanelli M (2006) Spectroscopic study of a Ni-bearing gahnite pigment. Journal of the European Ceramic Society 26. 317–321. 

• Hålenius U, Andreozzi, GB, Skogby H (2010) Structural relaxation around Cr³⁺ and the red-green color change in the spinel (sensu stricto)-magnesiochromite (MgAl₂O₄-MgCr₂O₄) and gahnite-zincochromite (ZnAl₂O₄-ZnCr₂O₂) solid-solution series. American Mineralogist 95, 456–462.
• Fregola RA, Skogby H, Bosi F, D'Ippolito V, Andreozzi GB, Hålenius U (2014) Optical absorption spectroscopy study of the causes for color variations in natural Fe-bearing gahnite: Insights from iron valency and site distribution data. American Mineralogist 99, 2187–2195.

• Stephan T, Henn U, Müller S (2022) On the Colour Mechanism of Blue Gahnite from Nigeria. The Journal of Gemmology 38, 183-193.
• Pluthametwisute T, Wanthanachaisaeng B, Saiyasombat C, Sutthirat C (2022) Minor Elements and Color Causing Role in Spinel: Multi-Analytical Approaches. Minerals 12, 928. https://doi.org/10.3390/min12080928
  
• Jaisanit N (2023) A "Cobalt Blue" Gahnospinel. Gems & Gemology 58, 476-477,