Are Granite Counter Tops Really Granite? A Petrographic Analysis of Decorative Stones (2009)

Undergraduates: Miquela Ingalls, Spring 2009 Igneous and Metamorphic Petrology Class

Faculty Advisor: Allen Glazner
Department: Geology

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The United States is the world’s largest consumer of dimension stone (an industrial term for any naturally-occurring rock material that is quarried and shaped for a specific application or use). In 2008, domestic dimension stone production/consumption was valued at $288 million for 1.45 million tons of finished product. An additional $2.5 billion worth of dimension stone was imported primarily from Italy, Brazil, Turkey, and China in the same year.

One of the most common forms of dimension stone is as countertops in businesses and homes. However, listings of available countertop styles have almost every variety labeled as granite. How accurate is such a description? Are the vast majority of countertops truly granitic, and, if not, what are they composed of and where did they come from?

In this research study our class investigated the compositions, characteristics, and origins of the rocks making up several different countertop slabs. Textural, elemental, and mineralogical data was obtained by hand sample analyses and with use of a scanning electron microscope (SEM). The original source (country, quarry, etc.) of the rock in each slab was determined and employed in conjunction with the appropriate chemical and petrographic information to properly identify the rock type and to construct its history of formation. Finally, the compositional and historical summaries for all samples were compiled for access by the general public.