Most mineraloids form at the low temperatures and low pressures found at Earth’s surface and in shallow subsurface environments. Materials such as opal, psilomelane, chrysocolla, limonite, and a wide variety of supergene materials crystallize from gels or colloids in the shallow subsurface. Many of these materials will eventually transform into minerals with time, heat, or pressure. These low-temperature mineraloids often have a mammillary (smoothly rounded or hemispherical), botryoidal (grape-like clusters), pisolitic (pea-like clusters), or stalactitic (icicle-like) habit.