Acicular (crystal habit)

Natrolite showing acicular crystal habit

Acicular, in mineralogy, refers to a crystal habit composed of a radiating mass of slender, needle-like crystals. Minerals with this habit tend to be fragile and complete, undamaged specimens can be uncommon.

Examples

Some minerals with an acicular habit include mesolite, natrolite, malachite, gypsum, rutile, and brochantite.^[1]

Differences From Other Habits

Some minerals like creedite form prismatic crystals that appear to be acicular, but are instead prismatic in a bladelike form; these can be told apart by the fact that all prismatic crystals are less sharp, sometimes are tipped with a pyramidal shape, and keep a standard cross-section shape with straight edges. Acicular crystals differ from fibrous crystals in their thickness; crystals with a fibrous habit are much thinner, sometimes to the point of being flexible like har, while acicular crystals are thicker and rigid.