Background

Granite is a very common intrusive igneous rock. It is coarse-grained and is composed of the minerals feldspar, quartz and biotite and muscovite mica. It has high silica content and occurs only in continental crust. Granites are light-colored, usually in grays and pinks, their color being determined by the color of the feldspar in the granite. Darker granites and even green granite are known.

Granite is very hard and dense. It can be readily cut into very large blocks and it takes an extremely high polish. Weathered granite, by comparison, crumbles easily. When granite is weathered and eroded, the feldspar and mica break down into clay minerals, leaving the very resistant quartz grains behind. Most beach sand is composed of quartz grains derived from granite.

Granite can contain a number of accessory minerals including apatite, magnetite and zircon. When superheated, element-rich waters alter granite, a variety of rare minerals are deposited in spaces in the granite, such as tourmaline and topaz. The feldspar in granite contains radioactive elements. The breakdown of these elements releases radiation, which turns colorless quartz crystals in the granite into black smoky quartz crystals.
The name granite is derived from the Latin word granum, which means grain, an obvious reference to the granular texture of granite.

Sources

As indicated above, granite is typical of and widespread in continental crust. Much of the North American continent is underlain by granite. The Canadian Shield is an extensive region of central and eastern Canada of massive granite (mixed with some metamorphic rocks) that covers approximately 1.7 million square miles. It extends into northern and northeastern United States. It is also called the Precambrian Shield because it first formed in the Precambrian Era over 545 million years ago. Some of the Shield is as old as 2 billion years. By contrast, granite also occurs in small, local intrusions called stocks.

Sources of commercial granite are found throughout the United States. New Hampshire and Vermont produce significant quantities of crushed granite and even more as dimension stone. The official nickname of New Hampshire is "The Granite State." Massive blocks of granite are quarried and shipped all over the United States for buildings, monuments, memorials (including carvings, headstones, mausoleums, etc.) and sculptures. Barre, Vermont is known for its granite quarries and calls itself "The granite capital of the world." Elberton, Georgia, another producer of fine granite, also considers itself "the granite capital of the world." The Elberton granite deposit is 35 miles long, 6 miles wide and about 3 miles deep.

Granite has different colors depending on the color of its feldspar. Different regions of the United States produce different colors of granite. For example, light and dark gray granite is quarried in Vermont, North Carolina and Georgia. Oklahoma and South Dakota produce red and pink granite. White and pink granite is produced in New Hampshire. Other states producing granite products are Arkansas, Colorado, California, and Maine. To summarize, granite is quarried from New England to the Southwestern United States and in many states in between.

Granite is also quarried in Canada, India and Brazil, Finland, Norway, Portugal, Spain, Namibia, Zimbabwe, and South Africa, to name but a few countries.

Uses

There is an enormous abundance of granite throughout the United States, so it is not a surprise that a significant amount of granite is used in crushed stone applications. Crushed granite represents 16% of the total crushed stone produced in the U.S., and it is the second-most utilized crushed stone in the U.S. Crushed limestone is by far the most commonly used crushed rock in the U.S., representing 70% of total crushed rock consumption. The 16% represented by crushed granite (265,000 tons per year) is used in road construction and railroad beds. Larger pieces of granite are used to stabilize the land around roadways to minimize and even eliminate soil erosion.

Granite is used extensively as dimension stone. It is used in the construction of buildings, both as building blocks and as veneers on frame structures. Because it can be smoothed to a very high polish, granite has found extensive use in memorials, headstones, monuments, carved decorations on buildings, statues and the like. Approximately 1.5 million tons of dimension stone is produced annually in the United States. Of this, granite accounts for over 400,000 tons (27%), second only to limestone.

Substitutes and Alternative Sources

Granite is enormously abundant and easily accessible in many parts of the world. In regards to crushed stone, there are plenty of options, limestone being the most commonly used, for crushed stone applications such as road construction, railroad beds, concrete, etc.

The limitations on the availability of granite for construction purposes (that is, as dimension stone) are related to particular colors, grain size and even patterns in the local stone. A review of the distributors of granite products shows that each granite quarry produces a stone with its own particular color and overall appearance. It is conceivable that granite with a particular look will eventually be quarried out at a particular quarry. However, granite as a commodity will continue to be abundant, easily accessible and economically profitable for countless generations to come.

By Darryl Powell

Darryl Powell is a 1984 graduate of the University of Rochester, Rochester, New York with a B.S. in Geological Sciences. For six years Mr. Powell was an Adjunct Professor at Finger Lakes Community College in Canandaigua, New York, where he taught "Introduction to Physical and Historical Geology." He creates Earth Science educational kits for NeoSCI, Inc., a science education resource company based in Rochester, New York. He also writes Earth Science materials for NewPath Learning, Inc. based in Victor, New York. Mr. Powell is the founder of Diamond Dan Publications, a small company focused on creative activity books and activity-based learning games about rocks and minerals, based in Manchester, New York.