Genesis of chrysoberyl in the pegmatites of southern Kerala, India

Abstract

ABSTRACT. In southern Kerala, India, chrysoberyl occurs in granitic pegmatites in association with quartz in alkali feldspar and is thought to crystallize earlier than beryl and sillimanite. The pegmatites are thought to have derived from the residual melts of granitic liquids formed by partial melting of the khondalites. In the absence of pyrometasomatic, desilication or aluminium-contamination processes, the genesis of chrysoberyl is explained by the CO 2 activity in residual melts. This model is at variance with the known concepts and may also explain the genesis of chrysoberyl in Sri Lanka where it is still controversial.

Chrysoberyl-sillimanite association from the Roncadeira pegmatite, Borborema Province, Brazil: implications for gemstone exploration

“…S2), which homogenize at c. 400 °C in the fluid phase. With respect to high CO 2 activity and homogenization temperatures, our preliminary results resemble those reported by Soman and Nair (1985) from Cbl occurrences in pegmatites from Kerala, India, and Petersen et al (2002) in kyanite-garnet-mica schists and quartzites from Minaçu, State of Goiás, Brazil. The primary pegmatitic origin of the Cbl was presumed by the former authors, while the metamorphic origin was proposed for the Brazilian occurrence.…”

Gahnite, chrysoberyl and beryl co-occurrence as accessory minerals in a highly evolved peraluminous pluton: The Belvís de Monroy leucogranite (Cáceres, Spain)

“…Chrysoberyl from the Belvís BU has FeO contents ranging from 0.44 to 0.60 wt.%, much lower than those from metamorphic rocks (2.5 to 3.2 wt.%; Downes and Bevan, 2002) or metamorphosed pegmatites (1.79 wt.%; Franz and Morteani, 1984), and slightly lower than in granitic pegmatites ( 0.67 to 1.3 wt.%; González del Tánago, 1991 ;Sornan and Nair, 1985; Fig. 11A).…”

“…This mineral association has only been described in Na-metasomatized pegmatites (Alfonso and Melgarejo, 2008 ), but chrysoberyl was interpreted as a secondary product of beryl replacement Beryl is a common accessory mineral in rare-element granitic pegmatites (Alfonso and Melgarejo, 2008;Cerny et al, 2003;Charoy, 1999;Rao et al, 2011 ;Thomas et al, 2009Thomas et al, , 2011Tindle and Breaks, 1998;Uher et al, 201 O), or in highly evolved granites (Charoy, 1999;Charoy and Noronha, 1996). Occasionally, it has been found associated with chrysoberyl in Be-rich pegmatites (González del Tánago, 1991;Sornan and Nair, 1985). The mineral association gahnite + chrysoberyl has been previously found in sorne Al-rich pegmatites Qacobson and Webb, 1947 ), but never associated with beryL However, gahnite micro-inclusions in large pegmatitic beryl crystals have also been reported (Uher et al, 201 O;Zhaolin et al, 1999), although interpreted as crystallized from an immiscible melt included during the beryl crystal growth.…”

Geographic Origin Determination of Alexandrite

“…Chrysoberyl has been mined in five Indian states-Kerala, Madhya Pradesh, Odisha (formerly Orissa), Andhra Pradesh, and Tamil Nadu-since the 1980s and '90s. Alexandrite is found there either in pegmatites intruding granitic rock or in biotite schists developed along the contact zone of pegmatites and peridotites (Soman and Nair, 1985;Patnaik and Nayak, 1993;Newlay and Pashine, 1993;Panjikar and Ramchandran, 1997;Valentini, 1998).…”