Rocks and Minerals:  The Allen County Museum has an extensive rock and mineral exhibit. Most of the minerals were collected and donated by James MacDonell. Some of the specimens are rare including large samples of topaz and “angel wing” calcite.  As dazzling as the real thing, the “Herkimer Diamond” quartz pocket, excavated in Herkimer County , New York , was believed to have been formed about 500 million years ago.  Igneous, sedimentary and metamorphic rocks are displayed with some spectacular samples of lava, pumice and obsidian.  The museum also has a dark room display illustrating the way in which some minerals react to ultra-violet light.