Some questions to Ask-a-Geologist are so off-the-wall that they rock me back on my heels and make me really think. Here's an example:
Q: is there a type of rock that dries faster than another?
- Shea P.
A: That's an interesting - and delightfully atypical - question. There are at least two issues involved:
- 1. The rugosity (or ruggedness) of the rock's surface. The smoother it is (like obsidian), the less surface is exposed to water and the less available in the way of nooks and crannies to trap and hold water. A sandstone would likely keep some moisture on it's surface longer than obsidian would.
- The surface tension/hydration of the rock's minerals. Certain minerals like clays adsorb (some also absorb) water on their surfaces in a pretty strong manner. Bentonite, for instance, will expand on contact with water and it takes forever to dry it out. When I lived in Denver I noticed that the ground sloped up to foundations of our tiny new house. I was emphatically warned by the realtor to not disturbed that grading. If water got under the eaves of my house, he told me, it could be funneled up against the side, and I could get heaving and major cracks in the basement walls as the swelling clay crushed into the concrete.
- Is the entire rock in contact with air, or is some of it buried?
- What is the humidity of the air?
- Is the air circulating?