• (n.) Minute acicular or dendritic crystalline forms sometimes observed in glassy volcanic rocks.
(from the article `crystallite`) ...faster-growing faces of a crystallite become smaller, so that the slower-growing faces are the longer ones. Rodlike crystallites composed of a ...
Bel'o·nite noun [ Greek ... a needle.] (Min.) Minute acicular or dendritic crystalline forms sometimes observed in glassy volcanic rocks. 
Belonites are minute acicular or dendritic crystalline forms sometimes observed in glassy volcanic rocks.