Is onyx a good medium for carving?

["Simon Brown" <moonsong@zzzzzzzzzzzzzzz>]

Tim,

The gemstone onyx is formed from silica, although some stone companies
market varieties of calcite under the name onyx because of their
translucent, banded appearance.

If you can get your material as boulders, it's likely to be calcite. Try the
acid test- a few drops of dilute acid will produce a bubbling reaction on
calcite but no reaction on silica.

If your stone is calcite, treat it the same as marble. The usual care with
cracks and inclusions applies.

If it is silica, it will be much harder and more brittle to carve, but will
still polish well- treat it like granite.

Simon