Ceiling tile for rock strata

A while ago, I believe that someone asked which kind of ceiling tile worked well to depict rock strata. I've seen ct used for this, but I was curious
about what kind to use as well. Now that I'm in need of a rock face after a mountain cut is complete, I'd like to add my question to his as well... what kind or kinds of ceiling tile works well for rock strata? I'm working in HO scale.
Thanks.
dlm --------------------------- Dan Merkel
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Dan Merkel wrote:

Look for some older tile that give a nice looking edge when broken.
The new tile I have checked is made from finer grind material and does not break like some of the tuff from 30 years ago.
So find someone that is remodeling or maybe an abandoned house.
Howard
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in article 4oQ2h.1018$ snipped-for-privacy@bignews4.bellsouth.net, Howard R Garner at snipped-for-privacy@bellsouth.net wrote on 11/3/06 3:41 PM:

Just make sure that the tile you use is asbestos free. Many types of old ceiling tile contained that hazardous substance when can cause health problems, including mesotheoloma, years later. It is safe enough when undisturbed or encapsulated (painted over), but breaking it up frees the fine fibers which cause problems. I would not even trust a filter mask to protect me, I would just avoid it.
--
Ed Oates
http://homepage.mac.com/edoates
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