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A transparent to translucent glassy mineral, essentially aluminum beryllium silicate, Be3Al2Si6O18, occurring in hexagonal prisms and constituting the chief source of beryllium. Transparent varieties in white, green, blue, yellow, or pink are valued as gems.
[Middle English, from Old French, from Latin bēryllus, from Greek bērullos, from bērullion, from Prakrit veruliya, from Pali veḷuriya; perhaps akin to Tamil veḷiru or viḷar, to whiten, become pale.]
ber′yl·line (-ə-lĭn, -līn′) adj.