So-called "geyserite" is a variety of opal formed in fumarole deposits. Apparently these were collected by a Dr. Leidy in 1877 on a trip, and brought back to give to the Academy for its collections. Half a dozen samples were here, all with the same number handpainted on the backsides, denoting common origin. This piece comes with a copy of the original label. NOTE: Collecting in the park is prohibited today.