Optical Spectra of Epidote, Ca₂(Al₂Fe)[Si₂O₇][SiO₄]O(OH) 

• Grum-Grzhimailo SV, Brilliantov NA, Sviridov DT, Sviridova RK, Sukhanova ON (1963) Absorption spectra of crystals containing Fe³⁺ at temperatures down to 1.7 K. Optika i Spektroskopiya 14, 228-233 (in Russian)
• White WB, Keester KL (1966) Optical absorption spectra of iron in the rock-forming silicates. American Mineralogist 51, 774-701.
• Burns RG, Strens RGJ (1967) Structural interpretatoin of polarised absorption spectra of Al-Fe-Mn-Cr epidote. Mineralogical Magazine 36, 204-226.
• Marfunin AS, Mineeva RM, Mkrtchyan AR, Nyussik YM, Fedorov VE (1967) Optical and Moessbauer spectroscopy of iron in rock-​forming silicates. Izvestiya Akademii Nauk SSSR, Seriya Geologicheskaya (1967), 86-102. (In Russian)
• Burns RG (1970) Mineralogical Applications of Crystal Field Theory. Cambridge University Press, 1970, p66-67.
• Parkin KM, Burns RG (1980) High temperature crystal field spectra of transition metal-bearing minerals: Relevance to remote-sensed spectra of planetary surfaces. Proceedings of the 11th Lunar and Planetary Science Conference 1, 731-755.
• Burns RG (1994) Mineralogical Applications of Crystal Field Theory. Cambridge University Press, Cambridge, 2nd ed. 551 pages.
• Petrusenko SI, Taran NM, Platonov AN, Gevorkyan SV (1992) The investigation of minerals of the epidote group from deposits of Rhodopy's area by methods of optical and infrared spectroscopy. Reviews of the Bulgarian Geological Survey 58, 1-9. (In Russian) 
• Taran MN, Langer K (2000) Electronic absorption spectra of Fe³⁺ in andradite and epidote at different temperatures and pressures. European Journal of Mineralogy 12, 7-15. 
• Liebscher A (2004) Spectroscopy of Epidote Minerals. Reviews in Mineralogy & Geochemistry 56, pp. 125-170.

Optical Spectra of Clinozoisite, Ca₂Al₃[Si₂O₇][SiO₄]O(OH) 

• Reddy BJ, Sarma KBN (1982) Absorption spectra of Mn²⁺ in manganoan clinozoisite. Acta Physica Academiae Scientiarum Hungaricae 52, 117-122.
• Schmetzer K (1982) Absorptionsspektroskopie und Farbe von V³⁺-haltigen natūrlichen Oxiden und Silikaten - ein Beitrag zur Kristallchemie des Vanadiuiims. Neues Jahrbuch für Mineralogie Abhandlungen 144, 73-106.
• Taran MP, Platonov AN, Petrusenko, S.; Khomenko VM, Belichenko VP (1984) Optical absorption spectrum of manganese(3+) ion in natural clinozoisites. Geokhimiya, Mineralogiya i Petrologiya 19, 43-51. Sofia, Bulgaria Academy of Science (In Russian)

Optical Spectra of Piemontite, Ca₂Al₂Mn(Si₂O₇)(SiO₄)O(OH)

• Abu-Eid RM (1976) Absorption spectra of transition metal-​bearing minerals at high pressures. RGJ Strens, editor. Physics and Chemisry of Minerals and Rocks, NATO Advanced Study Institute. "Petrophys." (1976), 641-75.
• Langer K, Abu-Eid RM (1977) Measurement of the polarized absorption spectra of synthetic transition metal-​bearing silicate microcrystals in the spectral range 44,​000-​4,​000 cm^-​1. Physics and Chemistry of Minerals 1, 273-299.
• Kersten M, Langer K, Almen H, Tillmanns E (1988) The polarized single crystal spectra and structures of thetic thulite and piemontites, Ca₂Al_3-pMn³⁺[O/OH/SiO/SiO], with 0.5 < p < 1.6. Zeitschrift für Kristallographie 185, 111.
• Langer K, Tillmanns E, Kersten M, Almen H, Arni RK (2002) The crystal chemistry of Mn³⁺ in the clino- and orthozoisite structure types, Ca₂M₃³⁺[OH|O|SiO₄|Si₂O₇]: A structural and spectroscopic study of some natural piemontites and “thulites” and their synthetic equivalents. Zeitschrift für Kristallographie 217, 563-580.