Several minerals give off a distinctive odor in certain conditions. A sulfur specimen, in normal room conditions, gives off a mild odor resembling the smell of a lighting match. However if heated or struck, it gives off a powerful odor like rotten eggs. Many sulfides, such as pyrite, also give off a rotten-egg odor if heated or struck.
An arsenic specimen gives off a very mild garlic smell in normal room conditions. However, if heated or struck, it gives off a powerful garlic odor. Some minerals containing arsenic, such as arsenopyrite, also give off a garlic odor if struck or heated. One should never heat a mineral that possibly contains arsenic; its fumes are toxic.
If wet or in moist conditions, minerals of the clay group, such as kaolinite, give off an odor resembling fresh clay.

Although only few minerals have a characteristic odor, odor is very useful identification key.

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