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PART V. SERPENTINOITS ROCKS. CHAPTER I. SERPENTINE. Sp. gr. 2.5-2.7. Contains silica 38.49-44.22 per cent. Of all the stones used for decorative purposes in architecture, none surpass in general estimation some of the varieties of serpentine. This is due both to the richness and variety of its colouring, and its capability of receiving a fine polish. It is not, however, adapted to outdoor use, especially in the smoky or gaseous atmosphere of cities; for, being acted on by hydro chloric and sulphuric acids, it is liable either to decay, or to become tarnished on the surface. Rut, for indoor decorations, and the construction of slender shafts, pilasters, pedestals, vases, inlaid slabs for walls, and ornaments of various kinds, serpentine is often em ployed with successful results. Mineralogists have separated this rock into the following varieties:—1. Precious, or noble serpentine, comprising the purer translucent and massive varieties, with a rich oil-green colour. 2. Common