According to Massachusetts General Law chapter 272, section 41:
"Whoever wilfully disturbs persons assembled in a public library, or a reading room connected therewith, by making a noise or in any other manner during the time when such library or reading room is open to the public shall be punished as provided in the preceding section."
The preceding section of the law cites a penalty of 30 days in jail or $100 fine, or both.
These days, more and more libraries are encouraging people to talk and interact in libraries, so this may be a moot point for you. However, just remember to try to be considerate of others while in the library. After all, isn't considerateness what laws are really all about?