Probably the biggest fear people have of natural stone is its maintenance. Truthfully, natural stone requires about the same level of care and maintenance as any countertop or floor, and certainly no more than natural wood products like tables and chairs.
The best care you can give your natural stone is preventative care. Preventing stains or scratching before they happen is far easier than getting rid of them after the fact.
Granite countertops are surprisingly resilient to stains, and practically impossible to scratch. But, as a preventative measure, wipe up any spills on the countertops within a reasonable amount of time. Don't let liquid sit on countertops overnight. Granite is most prone to staining by oil and acid, so blot these spills up soon after they happen, and then clean the stone with mild soap and water.
Marble countertops and tabletops are easily stained by acidic foods like fruit, tomato sauce, coffee, and wine. Blot, do not wipe, any spills up immediately, and then clean with mild soap and hot water. Do not set hot pans directly onto marble. And place a mat or pad between marble and anything which might scratch it, like a pan or utensils. Use coasters between marble and any glasses, especially ones containing acidic compounds like fruit juices, wine, or coffee.
On floors, the best preventative measure is regular cleaning. The movement of dirt and grit as it is ground into marble or granite tiles can wear away the finish. So the regular use of a dust mop can help keep dirt off the floor and preserve the finish. Use mats at all entry points to further ensure the long life of your floor's beautiful finish. Wet mop regularly with very hot water, and change the rinse water frequently. If the floor is particularly dirty, the use of a neutral stone cleaner or a mild dish detergent (one that is not oil-based) is perfectly acceptable.
In bathrooms, marble and granite tend to attract soap scum, just like manmade tile. Keep a squeegee handy for shower walls, and rinse vanities and natural stone sinks with hot, clean water regularly. Then towel them dry.
The use of sealers is also a powerful preventative measure. For countertops, ask your dealer if a sealant was applied before installation. If not, get his recommendation for a high-quality, food-grade sealer and apply it according to the manufacturer's directions. You will need to reapply this sealer periodically. The frequency of applications will depend on the sealer, and on the type of stone you have. Penetrating sealers are also available for flooring and bath areas. Likewise, the application of additional coats of sealer will depend on the type of stone, the frequency of use, and the manufacturer's recommendations.
If stains and scratches do occur, there are many things you can do on your own to remove them. On granite countertops, remove oil-based stains with acetone, mineral spirits, or bleach or ammonia diluted in water. (NEVER mix ammonia and bleach!) Food stains like coffee, tea, or fruit juices can usually be removed with hydrogen peroxide, combined with a few drops of ammonia. On marble countertops, avoid harsh cleaners and acidic cleaners, including vinegar.
For stubborn soap scum in the bath, ammonia can be used sparingly. Ammonia will, over time, dull the finish on marble, so use it with caution, and only when the soap scum cannot be removed with a mild, neutral detergent and hot water.
Water spots and rings occur because of minerals in water, and can be removed by buffing the spots gently with 00 steel wool. Likewise, small nicks and scratches can often be removed the same way. Larger scratches, nicks, and pesky stains may require professional help, which can be located by calling your local stone dealer.
And above all, DON'T let the fear of maintenance for natural stone scare you into avoiding it. There is no substitute for natural stone when it comes to beauty, practicality, and value. Keeping your natural stone beautiful is something you will enjoy, and no one ever regretted having chosen natural stone over its alternatives.