Large crystals of common scapolite (wernerite) are found in the apatite deposits in the neighborhood of Bamble near Brevik in Norway, and have resulted from the alteration of the plagioclase of a gabbro.

As silicates rich in calcium, it is to be expected that these minerals will be found where impure limestones have been crystallized by contact with an igneous magma.

Even marialite (the variety richest in soda) occurs in this association, being principally obtained in small crystals lining cavities in ejected blocks of crystalline limestone at Vesuvius and the craters of the Eifel in Germany.

The scapolites are colorless, flesh-colored, grey or greenish; occasionally they are nearly black from the presence of very small enclosures of graphitic material.

They are not in very perfect crystals, though sometimes incomplete octagonal sections are visible; the tetragonal cleavage, strong double refraction and uniaxial interference figure distinguish them readily from other minerals.

In some of these rocks large crystals of one of the scapolite minerals (an inch or two in length) occur, usually as octagonal prisms with imperfect terminations.

From these districts also a black variety is well known, filled with minute graphitic enclosures, often exceedingly small and rendering the mineral nearly opaque.

Extensive recrystallization often goes on, and the ultimate product is a spotted rock with white rounded patches of scapolite surrounded by granular aggregates of clear green hornblende: in fact the original structure disappears.

It has been suggested that the conversion of their original feldspar (for there can be no doubt that they were once gabbros, consisting of plagioclase and pyroxene) into scapolite is due to the percolation of chloride solutions along lines of weakness, or planes of solubility, filling cavities etched in the substance of the mineral.

This suggests that a pneumatolytic process has been at work, similar to that by which, around intrusions of granite, veins rich in tourmaline have been formed, and the surrounding rocks at the same time permeated by that mineral.

In the composition of the active gases a striking difference is shown, for those that emanate from the granites are mainly fluorine and boron, while those from the gabbro are principally chlorine and phosphorus.

The analogy is a very close one, and this theory receives much support from the fact that in Canada (at various places in Ottawa and Ontario) there are numerous valuable apatite vein deposits.

One series is essentially igneous (orthogneisses); usually they contain pale green pyroxene, a variable amount of feldspar, sphene, and iron oxides.