Figure 1.
The five stone samples used as test objects in the experiments—(a) granite; (b) sedimentary rock; (c) limestone; (d) marble; and (e) sandstone.
Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.