Characteristics of Natural stones

Even at the outset, one should know that all stones, used for decorative and finishing purposes, are not alike – though some of them may look similar, they are not identical. The natural stones can be broadly classified as belonging to three predominant groups - Igneous, Sedimentary and Metamorphic. Experts suggest that these differences are due to mineral components and the stone formation process.
Granite is a classic example of igneous rock that has cooled and crystallized beneath the earth’s outer surface. Sandstone, Coral stones, Limestone are some of the sedimentary type of natural stones.  Metamorphic denotes a change in form. This changing of one rock type into another type takes place due to an increase in temperature or pressure or a combination of both factors.
Colors of the natural stones depend on which part of the world they come from and on the nature of minerals in the earth through mining. As people may be aware blocks are removed from the quarry mines and then cut into slabs.
Each stone is obviously made up of different characteristics. Pitting is nothing to be abhorred as it does not make a stone inferior in appearance or quality. As a matter of fact, pitting is considered a natural characteristic of stone based on industry standards.
It may be purposeful to know some characteristics of various natural stones before buying natural stone products:
Granite is arguably the hardest natural material available for countertops.   Granite should be preferred not only for its beauty, but for its durability and easy maintenance. Granite can offer a wide range of color choices.
Marble is indeed a widely favored stone and many feel marble is irresistibly fascinating. Marble is also a hard material, though less hard than granite. But like granite, marble is available in multiple colors. Marble is ubiquitously used in hearths, pub counters, and bathrooms and to a lesser extent as kitchen countertops.
Limestone, it must be said, is a very porous material which offers a more rugged look – though many still prefer it.  Limestone is not an ideal choice for countertops because it is susceptible to staining and scratching and leaving indelible marks. Limestone may instead used for flooring, and fireplace adjoining areas. Limestone is also available in different colors.   
Soapstone is less favored by many for countertops as the appearance steadily darkens with age due to oxidation process. Soap may be appealing to a select few who desire an aged or weathered look for their countertops
Onyx is widely recognized as a gemstone. It is a semiprecious variety of quartz that is used often in jewelry-making. Onyx is a very aesthetic stone with variegated spots and layers - though somewhat fragile. Onyx is mostly used for furniture, fireplace surrounds and bar tops but may not be suited for kitchen countertops..

The important characteristics to be considered by the buyer of natural stones are Durability, hardness, strength, range of colors and overall appearance. One cannot expect all these qualifications in one particular natural stone.
Some natural stones that have atmospheric Influences are ill-suited as kitchen or bathroom countertops. A very porous stone will absorb water, which may freeze and cause crystals near the surface to flake off. A persistent exposure of fresh surfaces to such atmospheric elements may sooner or later cause disintegration
However, a natural stone whose strength and durability are high, will have sufficiently good looks – and more so, if the appropriate color is chosen..