Harder than marble and softer than quartzite, granite’s blue/gray hues are formed by intrusive rock cooling processes that produce a durable igneous rock. Most granites contain potassium, sodium, and feldspar, which can give it a flecked grainy appearance. Water resistance and heavy durability make it a popular choice for high-use areas. Its high heat resistance also makes it a good choice for fireplaces and exteriors open to harsh sunlight or environments. Granite stains quickly when exposed to green wood, oils, mud, and a combination of alkali salts and organic matter. Sometimes, given time and depending on the outer treatment, these stains will work themselves out of the rock.