Distinctly developed crystals are, however, of rare occurrence; they are usually acicular with acute pyramid-planes and are repeatedly twinned on the prism.
Crystals of arsenic belong to the rhombohedral system, and have a perfect cleavage parallel to the basal plane; natural crystals are, however, of rare occurrence, and are usually acicular in habit.
Sometimes the same plant produces both kinds of leaves on different branches, or the young plants produce acicular leaves, while those of the older plants are squamiform.
It crystallizes in white or pale fawn-coloured acicular prisms or silky needles, and is soluble in alcohol and ether, and in loo parts of cold and 3 of boiling water; it is without odour and has an astringent and an acid taste and reaction.
Quinine of commerce is the neutral sulphate,C20H24N202 H2S04.8H20, which occurs in commerce in the form of very light slender white acicular crystals.