Types of Stone

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Granite is an igneous rock made up of primarily quartz, feldspar, micas, amphiboles, and a mixture of additional trace minerals. These minerals and their variation in abundance and alteration give granite the numerous colors and textures we see in granite countertops. Formally, granite is a plutonic rock that is composed of between 10 to 50% quartz (typically semi-transparent white) and 65 to 90% total feldspar (typically a pinkish or white hue).

Granite is an intrusive igneous rock, which means it was formed in place during the cooling of molten rock. Generally, the slower the molten rock cooled, the larger it's mineral crystals with K-Feldspar megacrysts forming in special circumstances greater than 5cm. During formation of granite it is buried below kilometers of rock and sediment necessary to produce enough heat to melt rock.

Of course, the granite we see today is near surface, and thus at some point was uplifted, causing overlying sediment to be shed via erosion. This transition from high pressure and temperature to atmospheric temperature and pressure can cause the granite to slightly expand and crack. This, in addition to seasonal variations in temperature can leave you with a weakened and less desirable granite to use for countertops.

Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite. Marble may be foliated. In geology the term "marble" refers to metamorphosed limestone, but its use in stonemasonry more broadly encompasses unmetamorphosed limestone. Marble is commonly used for sculpture and as a building material.

Granite is a type of rock that is partially composed of quartz, a mineral. Therefore, what exactly is a quartz countertop? You may initially think that a quartz countertop would be composed of a quartz arenite, a rock made up of at least 90% quartz.

This may remind you of a white sandy beach with a few brown and pink specs. The natural sorting of quartz on beaches is driven by mineral strength (I'll get to that below) and their differential weathering rates. As weaker minerals weather and erode relatively quicker than quartz, you are left with quartz as a predominant mineral in well weathered sediment systems (i.e. beaches) far from sediment source (i.e. mountains).

However, you will find that quartz countertops are actually man made and although they consist of 90% quartz, the rest of the countertop is composed of resins, polymers, and various types of pigments. This creates a very durable artificial rock without pores or cracks. The pigment is used to provide coloration that is naturally found in quartz arenite.

Quartzite is a nonfoliated metamorphic rock composed almost entirely of quartz. It forms when a quartz-rich sandstone is altered by the heat, pressure, and chemical activity of metamorphism. These conditions recrystallize the sand grains and the silica cement that binds them together. The result is a network of interlocking quartz grains of incredible strength.

The interlocking crystalline structure of quartzite makes it a hard, tough, durable rock. It is so tough that it breaks through the quartz grains rather than breaking along the boundaries between them. This is a characteristic that separates true quartzite from sandstone.

Onyx is a translucent, generally layered, cryptocrystalline calcite. It is a highly decorative material that has been used as a gemstone and as a decorative surfacing material. Many varieties of onyx include semi-translucent veining that may be backlit, creating a dramatic effect. Onyx was frequently used by the ancient Egyptians to create bowls and other decorative elements.

All onyx will acid etch when exposed to acidic foods such as lemons or tomatoes. Most onyx has a moderate absorption rating and will stain when exposed to oil and highly-pigmented liquids. All onyx has a very low abrasion resistance rating; it will scratch, stun and crack. All onyx has naturally occurring cracks and fissures.