Slate streak colors are used in mineralogy studies to classify properties of a mineral based on the shade of its crushed powder. When rubbed against a porcelain slate, minerals leave streak marks that assist in determining their chemical composition.
A mineral's color characteristics may appear differently in powdered form as opposed to exterior shade. Similarly colored minerals may be more easily identified if their slate streaks are compared, as each might produce a different shade of streak. Fragments of calcite and quartz, for example, appear externally indistinguishable but differ in slate streak color, as both manifest in a diverse variety of natural shades.