Re: marble and granite

Lngknife29@... wrote:
Subject: Re: marble and granite

most marble is the same hardness as quartz--that is if it hasnt weathered too
badly-
and thats a little harder than glass

[Where did you get this bit of misinformation? Not from working with both
materials, I'd guess. Marble is basically Calcium carbonate, with a Mohs
hardness of about 3.5 (it varies a little, but the hardest isn't more than
4. ). Quartz has a hardness of 7. Glass has a hardness of 6, or softer. The
Mohs scale isn't a linear scale, so while I don't think you can really say
quartz is twice as hard, it is very noticably harder (and considerably more
difficult to carve) . Try this simple test: Get a steel tool, like a
knifeblade. Try scratching a piece of marble. (Don't do this in a museum).
It scratches quite easily, leaving a mark and raising a little dust. Now
try this with your piece of glass. The knife, being about the same hardness
(although much tougher- this is a different matter) will slide over the
surface- no scratch, no dust. But a sharp piece of quartz will noticably
scratch glass. Weathering, by the way, doesn't affect the hardness of
marble, but it can affect its cohesiveness, which is also a different
thing.]

Andrew Werby
for more info on this sort of thing, read the alt.sculpture FAQs at:
http://unitedartworks.com

Andrew Werby - United Artworks
Sculpture, Jewelry, and Other Art Stuff
http://unitedartworks.com