  The discovery of magnetism by the ancient Greeks was enabled by the natural
occurrence of lodestone -- a magnetized version of the mineral magnetite.
Nowadays, natural minerals continue to inspire the search for novel magnetic
materials with quantum-critical behavior or exotic ground states such as spin
liquids. The recent surge of interest in magnetic frustration and quantum
magnetism was largely encouraged by crystalline structures of natural minerals
realizing pyrochlore, kagome, or triangular arrangements of magnetic ions. As a
result, names like azurite, jarosite, volborthite, and others, which were
barely known beyond the mineralogical community a few decades ago, found their
way into cutting-edge research in solid-state physics. In some cases, the
structures of natural minerals are too complex to be synthesized artificially
in a chemistry lab, especially in single-crystalline form, and there is a
growing number of examples demonstrating the potential of natural specimens for
experimental investigations in the field of quantum magnetism. On many other
occasions, minerals may guide chemists in the synthesis of novel compounds with
unusual magnetic properties. The present review attempts to embrace this
quickly emerging interdisciplinary field that bridges mineralogy with
low-temperature condensed-matter physics and quantum chemistry.
