Patuxent River stone
The Patuxent River stone is the state gem of the U.S. state of Maryland. According to official state records, it is a form of agate; however, it is in fact an iron-stained quartzite. Patuxent River stone is found only in Maryland, and its colors reflect the state flag.
The Patuxent River stone became the state gem effective October 1, 2004, through the passage of Chapter 272, Acts of 2004; Code State Government Article, sec. 13-319.