"Don Bruder" wrote in message
...
Actually, by my understanding, quartz is indeed a form of silica, but
the reverse isn't necessarily true. For piezo to be involved, the
crystal structure is important, and not all forms of silica have the
right structure. Silica in the form of quartz has the right structure.
Silica in most of its other forms doesn't.

Common 'silica' is an amorphous supercooled fluid. Some pundits even argue
that it continues to flow (albeit slowly) in its 'solid' state. I dunno.

Quartz is crystalline.

LLoyd