Science column: The diamond deposit in your backyard

(postindependent.com) - Under grubby soils of northern Colorado lies the nation's biggest diamond deposit. Its crystalline bounty was almost found by accident. In the late 1960s, Colorado State University geologists were studying some rather unusual, crumbly rocks northwest of Fort Collins. These drab-green exposures were notable because burrowing animals liked to tunnel through them and because only certain types of trees and bushes thrived atop them. The rocks also contained a variety of "indicator" minerals that tend to form under high temperature, high pressure conditions that prevail deep in the earth. The geologists mapped the distribution of these rocks and found they originally formed in a series of funnel-shaped volcanic pipes. The worn-down tops of the "kimberlite" pipes – named after Kimberly, South Africa, where they are abundant – are visible from outer space. They extend from southern Wyoming all the way down to the People's Republic of Boulder.
A decade or so after their discovery, a student was grinding down samples of these rocks so they could be examined under the microscope. They made an astounding observation. Rather than the rocks being ground down by the polishing grits and plate, the rocks were etching grooves into the polishing plate. The likely culprit? The hardest mineral in the world. Analysis of the wafer-thin rock samples by the professor down the hall provided confirmation. Diamonds!