Re: What different types of rocks are resistant to weathering ?

First thing you need to decide is what kind of weathering you mean. You may
find that certain rock types are better against one than the other. There 
are both physical and chemical reactions that can destroy the rock.

Chemical weathering generally results from the action of acids in the 
atmosphere. These may be natural (mostly H2CO3) or from air pollution
(HNO3, H2SO4).  Rock types that have component minerals that are 
attacked by these agents will be more readily weathered. For example, most
feldspars decompose into clays, mostly via acid and water.

Physical weathering can occur when water penetrates a stone and freezes. 
This puts terrific expansion force on the rock and can crumble it. Rocks 
with lots of grains (and thus, grain boundaries, which tend to be weak 
points) or porous (conglomerates, sandstones) are going to be more prone to
this kind of attack.

But all this gets difficult in practice. For example, take sandstone. It is 
mostly quartz, and that should mean great resistance to chemical 
weathering. But some sandstones are held together by redeposited carbonates
and others by redeposited silica. The former are going to crumble under
acid attack, but the latter won't.  Limestones or marble, on the other 
hand, are readily attacked by acids, but often very resistant to physical
weathering because they are essentially "one rock", with few grains, few 
cracks,and thus not very permeable to water.

For your experiments, then, I'd suggest that you work on two things:

	a. How much water can the rock absorb when wetted (especially with
a solution containing some acid)? This may be measureable if you have 
access to an accurate enough scale. You may try to conduct some stress 
cycling: soak the rock, freeze it, warm it, soak the rock, freeze it, warm 
it, etc. This is a common type of test in industry to see how well products
(all sorts, not just rocks) stand up to harsh conditions.
	b. What happens to the rock when exposed to typical atmospheric
agents, specifically acidic solutions of H2CO3, HNO3, or H2SO4? This
is probably harder to do, but you may be able to put an acid solution on
it and measure the amount of removed material by examining the cations
that the solution has liberated from the rock. This will require some 
quantitative analytical chemical tests for metallic cations like Al, Ca, 
Fe, Na and K. You might also gather some of your local rainwater and see 
what its pH is and how much of each acid may be in it.

I'd also suggest that you contact some local architects and civil 
engineers. They may have detailed data on real weathering rates of actual
rock types as quarried.