Halotrichous

Halotrichous is a term used in mineralogy and geology to describe a fibrous or hair-like crystalline habit. Minerals exhibiting halotrichous growth are characterized by the formation of delicate, thread-like crystals that often appear matted or felted. This habit is a result of specific crystallization conditions, where growth is favored along one crystallographic axis, leading to elongated, needle-like structures.

The term originates from the Greek words "hals" meaning salt and "thrix" meaning hair, reflecting the appearance of some halotrichous minerals, particularly those found in evaporite deposits. While not a mineral species itself, halotrichous is a descriptive term for the morphology of crystals of various mineral species. Examples of minerals that can display halotrichous habit include gypsum, epsomite, and various sulfates and chlorides.

The formation of halotrichous crystals typically occurs in environments with supersaturated solutions, such as saline lakes, arid regions, or hydrothermal veins. The precise conditions, including temperature, pressure, and the presence of impurities, influence the development of this fibrous texture. In some cases, halotrichous aggregates can form delicate, branching structures resembling moss or tiny hairs. The fragility of these crystals often means they are found in protected environments or as pseudomorphs after more robust structures.