(Chiefly of crystals) needle-shaped.The acicular crystals are sometimes intergrown or twinned, causing a distortion that results in seemingly single crystals with relatively fat bases tapering to pointed terminations....
All of the acicular crystals are late Neoproterozoic
The largest amphibole crystals are embedded in the rock matrix, whereas the smaller acicular crystals line the hollows.
Origin
Early 18th century: from late Latin acicula 'small needle' (diminutive of acus) + -ar1.