More on Rock Cork from Infoplease:

• Rock Cork - Rock Cork A variety of asbestos, resembling cork. It is soft, easily cut, and very light. Source: ...
• elm - elm elm, common name for the Ulmaceae, a family of trees and shrubs chiefly of the Northern ...
• Dictionary of Phrase and Fable: R - Definitions, origins, and illustrative excerpts for words, phases, and literary allusions starting with "R"