Acicular (crystal habit)

[1] Strictly speaking, the word refers to a growth habit that is slender and tapering to a point.

Prismatic crystals are not acicular; however, colloquial usage has altered the commonly understood meaning of the word.

When writing for mineralogical publications, authors should restrict their usage of "acicular" to crystals with the tapering growth habit.

Minerals with an acicular habit include mesolite, natrolite,[2] malachite, gypsum, rutile, brochantite and bultfonteinite.

Crystals of dimethyltryptamine have an acicular habit,[3] but this substance is not regarded as a mineral by the International Mineralogical Association.