This is a polyhedral representation of the crystal structure of the pyroxene diopside (CaMgSi₂O₆), which is part of a solid solution series of pyroxene compositions. The blue polyhedra represent the Si-O tetrahedra that are linked to create the basic chain structure of all pyroxenes. The magenta polyhedra represent the M1 cation site (filled by Mg), and the green atoms (shown with their bonds) are Ca atoms filling the M2 cation site. All of the molecules in the structure vibrate (stretching and bending along bonds), resulting in absorption features in the middle infrared portion of the EM spectrum. This view is looking along the C-axis of the mineral, parallel to the chains of Si-O tetrahedra.

This is the thermal infrared emission spectrum of diopside. If you are more familiar with reflectivity spectra, simply invert the spectrum. If you are familiar with transmission (absorption) spectra, this is not a comparable spectrum, although it may look similar.

Due to the nature of emission (or reflection) spectroscopy, and the complex nature of vibrational interactions in crystalline solids, the absorption features in this type of spectrum do not represent the actual vibrational frequencies of the mineral. Regardless, they are still diagnostic of mineral type, even in the minerals of a solid solution series. This characteristic allows us to distinguish all minerals from each other, including silicates, oxides, carbonates, etc. The same is true for rocks - every rock contains a different percentage of constituent minerals. Mineral spectra add linearly (in proportion to their abundance) in the spectra of rocks. The variable percentages of minerals in rocks allow us to discriminate not only between basalt, sandstone, schist, and granite, for example, but also between different compositions within each rock type. We can use linear deconvolution to determine the composition of Martian meteorites from their spectra.