vajra

[Rosati]

Greetings-

As a student of Buddhist Tantra, I am interested in how Indra's Vajra came
to have connotations like "adamantine" "diamond" "indestructible". I have
been looking at the occurrences in the Rigveda, and notice that it is
sometimes described as made or iron or metal and with edges (sounding much
like the Tibetan rdo rje). Macdonell mentions that it is "sometimes spoken
of as a stone or rock." Does anyone know what he is referring to, or of any
works or monographs on this interesting word?

Thank you

Dante Rosati
http://users.rcn.com/dante.interport/prajna.html