Surface weathering preduees coatings of mineral materials which may be similar to

or quite differeflt from

the minerals of the underlying parent rock. These coating are usually only microns to millimeters in thickness

but they completely control the reflectance spectra of the terrain. In a similar way coatings formed from adherence of wind-borne dusts

cemented or not

will also dominate the reflectance spectra as seen in remotely sensed imagery. Cemented coatings are often dark-colored （even black） and are usually termed "desert vanish" from their common occurrence in arid regions. Despite their featureless

dark color to our eyes

these coatings （often clays）

show characteristic reflectance minima in the short-wave infrared （SWIR） regions

by which their mineralogical composition can be deduced. Thus to relate remotely sensed imagery to actual ground "geology" reqinres a good knowledge of the surficial character of the exposed rock outcrops. It is not always possible to find "fresh" surfaces in the field

and one must always differentiate "upper-surface" spectre （and also "lower-surface" spectra） from the spectra of the "inner rock" materials. This paper describs the spectral effects in deeply-weatherad Mafic

Ultrabasic

and Felsic Rocks in arid terrains of the central Western Australia.