Hardrock

The federal system for "hardrocks," pursuant to the Mining Law of 1872, allows the discovery, location, and development of these minerals without payment to the federal government.

Source: wiktionary

Reflection coefficients calculated from impedance contrasts between felsic and mafic rocks and other common lithologies in hardrock terranes often exceed 6%, the estimated minimum value required to give strong reflections.

Source: wiktionary

In this context, you asked us to provide information on (1) which types of royalties the 12 western states assess on hardrock mining operations and (2) trends on imports and exports of hardrock minerals.

Source: wiktionary

The Western U.S. sample was separated into the recording site categories of hardrock ( i.e., crystalline rock outcrop) , intermediate ( i.e., sedimentary rock or thin alluvium) and alluvium ( i.e., thick alluvium), and average residuals were computed for each of the three subsets.

Source: wiktionary