The most abundant mineral of the veins is natrolite, which occurs chiefly in granular aggregates. Indications of crystal form are largely limited to the drusy cavities, and even there the natrolite generally forms in peculiar groups, projecting in small roof- shaped ridges or coxcomb-like forms, and only very rarely developing the prismatic forms usually characteristic of natrolite. Some of the druses are filled with very small needles of green or blue-green amphibole, and lying in the midst of the cavity supported by these needles the natrolite often occurs as equant[4] polyhedral aggregates of from 1 to 3 millimeters in diameter, not at all suggestive of the mineral natrolite. Most conspicuous and beautiful in this white ground of the natrolite gangue are the scattered idiomorphic Crystals of the blue equant or somewhat tabular benitoite and the brilliant black neptunite prisms, showing here and there a touch of deep red. These minerals are the characteristic and more abundant minerals of the benitoite-bearing veins.

In plate 30 it is apparent that surrounding the drusy cavity is a layer of white (natrolite) and that it is followed by a layer of darker color. This outer layer is of variable thickness - from a fraction of an inch up to several inches - and is usually pesent between the white vein material and the more definitely recognisable wall-rock. It has a bluish or greenish tint, and looked at closely is seen to show a granular structure with luster and cleavage much like the vein-stuff. It is indeed natrolite which is loaded with numerous microscopic

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