Mineral spring

Salts, sulfur compounds, and gases are among the substances that can be dissolved in the spring water during its passage underground.

[1][2] Sulfur springs smell of rotten eggs due to hydrogen sulfide (H2S), which is hazardous and sometimes deadly.

[3] The quantities ingested in drinking water are much lower and are not considered likely to cause harm, but few studies on long-term, low-level exposure have been done, as of 2003[update].

Historical mineral springs were often outfitted with elaborate stone-works — including artificial pools, retaining walls, colonnades, and roofs — sometimes in the form of fanciful "Greek temples", gazebos, or pagodas.

Spectacular formations, including terraces, stalactites, stalagmites and 'frozen waterfalls' can result (see, for example, Mammoth Hot Springs).