It has recently been shown that amorphization and melting of ice (O. M
ISHIMA, Nature, 384 (1996) 546) were intimately linked. In this letter
, we infer from molecular-dynamics simulations on the SiO2 system that
the extension of the alpha-quartz melting line in the metastable pres
sure-temperature domain is the pressure-induced amorphization line. It
seems therefore likely that melting is the physical phenomenon respon
sible for pressure-induced amorphization. Moreover, we show that the s
tructure of a ''pressure glass'' is similar to that of a very rapidly
(10(13) to 10(14) kelvins per second) quenched thermal glass.