Originally Posted by Londonee
Nice, just was driving down to DC and thought of that last weekend.
The white granite should be more brilliant and reflect light more than any white marble. The white marble on the Ritz(Girard Bank) is from the state of Georgia and is as dense as marble gets so it is very bright in sun light, particularly right after the restoration in 2000. City Hall is clad in a white marble from the state of MA and is somewhat course and collects dirt over time. If you are old enough you might remember it was almost black from soot from trains in the first half of the 20th c.
Granite is an igneous rock and was once molten so it is as dense as rock gets. Marble started out as limestone( a sedimentary rock) was then put under high heat and pressure causing the calcite in the limestone to recrystallize into larger crystal structures so it doesn't have the density of granite.
So what you see now, i.e., the grey concrete, will be transformed utterly.