Sandstone is the French grès of mineralogists, and its name clearly indicates the principal constituents. In fact it is formed more or less of minute fragments of different rocks united together by a cement. Sandstone appears in different gradations of colour and hardness. Some of them, on account of the vividness of their colouring and the polish they take, are ranked among the decorative stones, others are used for sharpening tools, and they are then called grindstones (pietre da arruotini).[p137]
553. (137.1) Pietra rota degli Appennini. Dark grey ground with broken dull reddish bands. (Common).
554. (137.2) Arenaria di Brianzo in the Milanese area. Light grey ground with many, small white spots. (Not common).
555. (137.3) Arenaria di Siena. Vivid red ground with some lighter spots verging on whitish. (Rare).
556. (137.4) Arenaria di Vigiù in the Milanese area. Dark green ground with yellowish waves. (Rare).
557. (137.5) Arenaria antica, so called because it is found in excavations. Ground of yellow that shades into grey with darker waves. Very beautiful, and (rare).
558. (137.6) Arenaria di Corsica. Ground of translucent apple green, and flowered with a yellowish green. (Common).
559. (137.7) Arenaria antica. Mixture of small particles of white, yellow, grey, and dark colours. Very beautiful, and (very rare).
961. (Suppl.21.1) Arenaria antica. Mixture of grey, white, yellow and black sands. (Very rare).