ROCKS

Directional hemispherical spectra of both solid (usually a freshly 
broken surface) and finely powdered (0-75 micrometer) igneous 
rocks were measured for the JHU collection.  The infrared portions of 
these spectra were originally published as a USGS Open File Report 
((Salisbury, J. W., Walter, L. S., and D'Aria, D. M., 1988, Mid-Infrared 
(2.5-13.5 micrometer) Spectra of Igneous Rocks: Open-File Report 
88-686)). 

Spectra of sedimentary and metamorphic rocks were measured both 
fine (0-75 micrometer) and coarse (500-1500 micrometer) 
particulate samples.  Spectra of the very coarse samples were meant 
to simulate spectra of freshly broken (rough) surfaces.