What is the difference between granite, marble, and limestone?
Granite is an igneous rock (etymology from Latin ignis, fire), primarily of volcanic origin, which is formed over millions of years under conditions of extreme heat and pressure from the crystallization of cooled magma. Granite is felsic in composition, meaning that it is predominately quartz, rich in silica, and contains feldspar and/or feldspathoids. The "Feldspar Crema" shown below is a classic example of a feldspar granite. Today, several types of igneous rock (volcanic in origin) are sold as "granite", such as basalt, syenite, and labradorite. The mineral composition of granite makes it an ideal kitchen work-surface because these minerals are immune to many chemicals found in foods and household cleaners. Granite is however a porous stone and should be sealed before use with a silicone based impregnator to prevent staining.
	Marble is a metamorphic, crystalline rock resulting from metamorphism of sedimentary carbonate rocks, either limestone or dolostone, into a new stone. It is extreme heat and pressure which causes the original calcite limestone to undergo this metamorphic process and causes a complete recrystallization of the original rock into an interlocking mosaic of calcite, aragonite and/or dolomite crystals. This violent transformation gives marble it's much appreciated texture and character, with it's large sweeping veins and dramatic variation in color. Pure white marble is the result of metamorphism of very pure limestone, while the swirls and veins of many colored marble varieties are usually due to mineral impurities such as clay, silt, and iron oxides, which were present as grains or layers in the original limestone. Marble can be polished to a high shine, but scratches and chips easily because it is soft in nature. Without proper sealing, marble stains easily. It must be sealed immediately after installation with a silicone based impregnator to protect it from staining and acid etching caused by contact with acids found in common foods and cleaners. Though marble is not as hard and stain resistant as granite, it's unique vein structure and array of colors is undeniable. Below is an example of a beautiful African marble called, "Ebony Gold". Marble is widely used today for both kitchen & bathroom surfaces. The customer who chooses to own marble countertops should be educated on limitations.
Limestone is a sedimentary rock, consisting primarily of calcite from marine organisms. It is formed through the cementing together of naturally accumulated rock fragments and organic sediments via a chemical process which occurs in shallow prehistoric marine environments. Crystals of quartz, calcite, domolite, or barite may line small cavities in the rock. Limestone is partially soluble in acid, and therefore needs to be properly sealed with a silicone based impregnator before use as a countertop work surface. Limestone can be crystalline in nature, depending on how it was formed. The densest varieties can be polished to a high shine. Limestone is quite durable and it's neutral colors make it an ideal flooring surface, even in high-traffic areas. Deposits of limestone are quarried on every continent (accept Antarctica), and throughout the millennia it has been used as a reliable building material. Displayed below is a picture of "Antique Golden" limestone from Egypt.
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