SAND-Stone, a compound stone, of which there are numerous varieties, arising not only from a difference of external appearance, but also in the nature and proportions of the constituent parts. See GEOLOGY Index.

There is a singular variety of sand-stone, which consists of small grains of hard quartz which strike fire with steel united with some micaceous particles. This variety is flexible and elastic, the flexibility depending on the micaceous part and softness of the gluten with which the particles are cemented. This clastic stone is brought from Brazil. There are also two tables of white marble, kept in the palace of Borghefe at Rome, which have the same property. But the sparry particles of their substance, though transparent, are rather soft, and may be easily separated by the nail. They effervesce with acids, and there is a small mixture of minute particles of talk or mica.

Sand-stones are of great use in buildings which are required to resist air, water, and fire. Some of them are soft in the quarry, but become hard when exposed to the air. The looser ones are most useful, but the solid and hard ones crack in the fire, and take a polish when used as grindstones. Stones of this kind ought therefore to be nicely examined before they are employed for valuable purposes.