Applications of nonlinear unmixing models based on the Shkuratov theory to fit laboratory spectra of intimate mixtures and to derive imaginary refraction indices of minerals are presented. The tests are performed using mafic minerals (pyroxenes, olivine, plagioclase). Abundance estimates of end-members are accurate to within 5--10% for the analyzed mixtures, while the estimate particle sizes are within the intervals of actual sizes, given the reflectance spectra of the end-members only. The type of mixture (areal versus intimate) can be tested. A quantitative modeling of basalt, a dark rock mainly composed of bright minerals, is also presented. The limitations of our modeling method are discussed.