Tourmalines from Bottino essentially preserve primary pre-metamorphic features. In particular, some tourmaline crystals show sharp, concentrical colour zones, interpreted to represent primary growth structures. Post-growth chemical exchange with fluids of probable metamorphic origin have led to the local development of discordant palecoloured tourmaline rims. Microprobe analyses reveal that growth and discordant zonings mainly depend upon Fe/(Fe+Mg) and Na/(Na+Ca) variations, respectively. Colour zoning of the crystals appears to be related to Ti content rather than to Fe/(Fe+Mg) variations. Except for (rare) discordant zoning, the effect of greenschist-facies metamorphism on tourmaline composition appears limited, as shown by the lack of systematic cation partitioning between coexisting tourmaline and metamorphic chlorite.
Mineral chemistry of tourmalines from the Bottino mining district, Apuane Alps (Italy) / Benvenuti M.; Costagliola P.; Lattanzi P.; Tanelli G.. - STAMPA. - Vol. I:(1990), pp. 5-6. (Intervento presentato al convegno 15th IMA Congress, tenutosi a Beijing (China) nel 28 June-3 July, 1990).
Mineral chemistry of tourmalines from the Bottino mining district, Apuane Alps (Italy)
BENVENUTI, MARCO;COSTAGLIOLA, PILARIO;LATTANZI, PIERFRANCO;TANELLI, GIUSEPPE
1990
Abstract
Tourmalines from Bottino essentially preserve primary pre-metamorphic features. In particular, some tourmaline crystals show sharp, concentrical colour zones, interpreted to represent primary growth structures. Post-growth chemical exchange with fluids of probable metamorphic origin have led to the local development of discordant palecoloured tourmaline rims. Microprobe analyses reveal that growth and discordant zonings mainly depend upon Fe/(Fe+Mg) and Na/(Na+Ca) variations, respectively. Colour zoning of the crystals appears to be related to Ti content rather than to Fe/(Fe+Mg) variations. Except for (rare) discordant zoning, the effect of greenschist-facies metamorphism on tourmaline composition appears limited, as shown by the lack of systematic cation partitioning between coexisting tourmaline and metamorphic chlorite.I documenti in FLORE sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.