A few of thoughts:
Marble will probably be a lot cheaper, but neither
will be as little as $40. I had to buy a 5 1/2" x
3/4 x 8' awhile back and I think that was $70. But
it was also a stock threshold. Custom pieces cost
more and often you have to pay for the whole sheet
if the stone shop doesn't have a scrap.
Marble is more typical in baths. (Downright common.)
It looks nice with something like white tile. Granite
would give you more creative design options.
If you use the marble, try to set it in a fair amount
of thinset. It's very brittle. I cut it on a diamond blade
tile saw easily, but it tends to snap off as it gets close
to the end of the cut. (You may have noticed that it's
not uncommon to see broken up marble thresholds in
bathrooms when people have made the mistake of just
setting it on the underlayment.) Granite, by contrast,
has a large percentage of quartz, which is hardness 7.
That may be its main down side, in addition to cost: A
child running or elderly person falling is a lot better off
hitting their head on marble than on granite.
Also, a side note: You can get a grinder fairly cheap
and tile places will sell different grits of grinding wheels.
Grinding finished edges and roundovers on marble, should
you need to, is actually fairly easy. It's so soft that there's
actually a risk of overgrinding. You have to do it carefully.
| I'm remodeling the downstairs bathroom. I have a raised ranch and on
| the lower level at the foundation top we have a very wide windowsill,
| about 8" or so. The walls will be porcelain tile up to about 5'. The
| present sill is wood so I'm thinking of either a marble or granite piece
| 3/4" thick.
| Is either of these materials not suitable for some reason? One better
| than the other? Cost is not going to be a big factor, when spending
| thousands of dollars already, forty bucks either way won't make much