Deposits of limestone are typically derived from the shells of creatures such as clams and certain microorganisms. Limestone, onyx, and travertine are all in the family of organic rock. In the stone industry, rock can be classified by geologic classes or groups. Granites are typically harder, denser, and more durable than calcareous stones, which are more vulnerable to common domestic acids, such as orange juice, milk and vinegar. Many homebuyers considering the use of natural stone ask whether marble, limestone, travertine, and onyx are porous, vulnerable to staining, water absorption, and scratching.
All stones are subject to scratching.
Fine stone is extracted from quarries on 6 different continents and from some islands as well. Blocks are cut out of the mountainside walls using drills or wires with abrasives embedded in them. Most blocks are about the size of a mini-van and weigh about 50,000 lbs. They are graded according to color, movement, structure and overall appearance, with some reserved for slab or tile production. The graded blocks are then sold to stone-processing factories around the world.