File:Lamproitic Volcanic Tuff from Arkansas.jpg

English: Lamproitic volcanic tuff (Prairie Creek Lamproite) of early Cretaceous age (~106 Ma) from the Crater of Diamonds State Park, south of Murfreesboro, Arkansas, USA.

This rock is from the only publicly-accessible diamond collecting site in America - Crater of Diamonds State Park, just south of Murfreesboro, in Pike County, southwestern Arkansas (34° 01’ 55” to 34° 02’ 05” North, 93° 40’ 18” to 93° 40’ 25” West). There, diamondiferous, lamproitic rocks of the Prairie Creek Lamproite (a.k.a. Prairie Creek Pipe) are exposed (actually, it’s just a field of rocky dirt). Diamonds are found by tourists on a daily basis. The Prairie Creek Lamproite is an ultramafic pipe that intrudes Proterozoic-aged (Grenvillian) basement rocks. Rocks of the Prairie Creek complex date to about 106 million years (mid-Albian Stage, late Early Cretaceous).

Three distinctive lithofacies occur at Crater of Diamonds - a lamproite pipe facies, a lamproitic volcanic breccia facies, and a lamproitic volcanic tuff facies. This pale bluish rock is from the tuff facies, although it does have obvious large fragments.