Many people, even educators, believe that the only places to see fossils are in museums, rock shops, books on paleontology, or perhaps in natural rock outcrops. They may not notice a treasure trove of fossils nearby in facades and lobbies of buildings, storefronts in malls, in rest room partitions, and even tabletops in furniture stores. In the last two decades, there has been an enormous increase in the use of natural rock in construction projects. Rocks used for building purposes are traditionally called building stones or dimension stones when they are cut to shape.

Responding to the marketplace and because the extraction of blocks of rocks is relatively easy once suitable materials are discovered, there has been a worldwide increase in the number of quarries, especially from third-world countries that may even lack the facilities for cutting and shaping the extracted block. Where no mills exist, the material is shipped to facilities sometimes a half a world away for shaping and finishing the stone for a particular project.

As a result of this large worldwide increase in quarry activity, a great variety of rocks from almost every division of the geologic column arrives in the marketplace.

For the teacher who wants to use this available resource for lessons, the first challenge is locating appropriate stones in a building or other structure. Excursions for lower grades may only require the teacher to name the rocks and point out obvious features such as fossils and bedding (for illustrations of fossils, see Arduini 1987 and Horenstein 1988). There are also numerous web sites about fossils. For a start, try http://www.ucmp.berkeley.edu/exhibits/index.php and http://www.fossils-facts-and-finds.com. At higher levels, geology teachers would want to include the rocks’ geologic occurrence. To eliminate confusion, stones in this paper are defined as rocks used by people—such as building stone, stone walls, stone pavements, and so on, while rocks are the materials found in their natural setting that have not been so used. Rock specimens used by students should still be called rocks.

If a teacher does not live in a community for which a guidebook or a list of stone installations has been written or compiled (see appendix), the next step is to find a stone dealer that is willing to help and who knows where the particular stones are installed (finding a local dealer or supplier on www.google.com, www.msn.com, and www.yahoo.com is easy: just list the state, or in many cases the city, and the resulting display in varying forms—mostly ads—will direct you to the business). Keep in mind that a guidebook for a distant city is not entirely useless, especially for stones that have a national or international distribution, especially if the guide contains images. Of course, some stones have only a limited local distribution, which the geology instructor would usually know about. Many guidebooks contain good examples for conducting excursions.

If you have the opportunity to look at available stone samples at a stone dealer’s store, do not be disappointed if the proprietor may only know the commercial name and perhaps where it comes from—Italy, for example. If you feel comfortable, you may also ask for samples of stones that are no longer available for sale but have been used in local buildings in the past. The labels will usually only have the commercial names on the stone as well as the dealer name. Surprisingly, some building managers may actually know the name of the stone used in their structure and perhaps where the material comes from. While there is considerable diversity in the exterior facades of buildings, including the interior lobby will often give the teacher a wider range of stone types. Many building stones are not suitable for exterior use but are for interior use. While in the past there usually was no difficulty in bringing a class into a lobby, today’s heightened security demands make it more difficult. Any field trip plans should include prior permission to visit.

Finding the information about a particular stone, especially older, no longer quarried types, may take a considerable amount of detective work, but that is the fun of it. After obtaining information about where a stone is quarried either from a stone dealer, guide, or organization such as the Marble Institute of America http://www.marble-institute.com or Building Stone Institute http://buildingstoneinstitute.org, searching the literature for geological information is made relatively easier by such index databases as Geoscience World http://geoscienceworld.org. Winkler (1997) provides an up-to-date text on the properties and durability of stone, and Hannibal and Park (1992) provides an extensive list of selected sources of information on building stones.

Particular stones may be popular for a while, then go out of production for a variety of reasons—such as changes in color tastes, weathering issues, or the quarry is no longer in, operation. The stones may no longer be wanted or quarried but to remain open the business may sometimes import blocks of stone from other quarries for sale. In that case, a stone can be said to be from a particular quarry when in fact it came from elsewhere. Building stones have great appeal because of their color, general appearance, and the geologic stories they tell, but you should be forewarned that if your main goal is to locate fossiliferous material, you will find the other groups of rocks equally compelling to your students who will want to know about them too.

Therefore, this article makes reference to all types of building stones. For the teacher uninitiated in geology, it does not take long to learn the three basic groups of rock classified on the basis of origin. Igneous rocks were once molten rock that forms deep in the earth’s crust and cools and crystallizes there (example: granite) or erupts onto the surface in the form of lava (example: basalt). Sedimentary rocks form on the land or in the sea and are layered and may contain fossils (sandstone, limestone). Shale is one of several sedimentary rocks that are not suitable as a building stone. Metamorphic rocks are rocks that have been changed by heat and or pressure, a process that also takes place deep below the surface. For example, a sedimentary rock containing fossils will lose all traces of life if the degree of metamorphism is great (Horenstein 1994) See also http://pubs.usgs.gov/gip/fossils.

Teachers with a basic knowledge of rocks may find such commercial descriptions as “black granite” somewhat confusing (Horenstein 1990). It turns out that in the building stones industry, for the most part, the term granite includes any hard rock that can be polished, which lumps almost all of the igneous (from granite to gabbro) as well as many of the metamorphic rocks (from various gneisses to quartzite) into this category. Most soft rocks that can be polished that are not “granite” are grouped together as marble and include true marble, many limestones, and serpentinites. Therefore, do not overlook stones with the commercial name “marble” or reject them as nonfossiliferous just because the name implies a metamorphic rock and where any fossils that may have existed in the original parent material were destroyed by metamorphism. The commercial designation limestone includes carbonate rocks that cannot be polished, while the metamorphic rock slate is in a category by itself.

The “Appendix” contains a selected list of guide books of particular cities as well as a list of building stone resources by state. It does not make reference to studies that are entirely devoted to granite, but an excellent web resource is http://quarriesandbeyond.org/index.html.

The scientific and semipopular literature for imported materials is enormous and much of it non-English, although many commercial listings on the web are also in English. In addition, publications directly related to the building and dimension stone industry have not been included here. Teachers who want to expand their knowledge of this multidisciplinary subject should consult, for a start, the magazine Stoneworld (http://Stoneworld.com). One excellent source for images of stones is http://stone.network.com and A Web Gallery of Stone Buildings and their Building Stones (http://gly.uga.edu/railsback/BS-Main.html), as well as the web pages of building stone suppliers, especially useful if a community is lacking in stone buildings.

Once you have the name of a fossiliferous (or any other) stone and its company or country of origin, find geologic information by starting with some research at http://www.geoscienceworld.com. Commercial names often do not give you much information. For example, “Crab Orchard Sandstone” is sandstone from Crab Orchard, TN, USA but the St. Genevieve Golden Marble is not a marble that was quarried in Ozara, St. Genevieve County, MO, USA but a Devonian age limestone containing colonial and rugose corals. Radio Black Marble on the other hand, used in Radio City Music Hall in New York, NY, USA is a black Ordovician limestone from Vermont containing large examples of the snail Maclurites sp., algae, crinoids, and early corals, but it is also called Champlain Black Marble. Many stones have multiple names for a variety of reasons related to the commercial aspect of stone sales, including competition with other dealers. As stated earlier, you will find fossils in buildings throughout the Phanerozoic (Paleozoic, Mesozoic, Cenozoic eras), but they are generally most abundant in rocks formed during the Ordovician, Devonian, Jurassic, and Cretaceous times when the continents were covered with large epicontinental seas.

It is an unhappy surprise when a favorite building stone disappears because its building is demolished or new owners remodel the lobby or facade. Normally, the material is not recycled into another building but is destroyed and ends up in a land fill. One hopes to find out about the renovation early so that some samples can be saved for class use. Awareness of alterations is important when using a guidebook, especially when the description of a stone just does not add up. One way to avoid this problem is only to visit historic landmarks. On the other hand, it is of interest to know why the alteration took place.

Most of my experience studying building stones has been in metropolitan New York. Unlike many other localities, New York City is endowed with numerous rock outcrops, often conveniently located in New York City parks. Although easily accessible, their diversity is limited to a small variety of metamorphic rocks and even smaller sampling of sedimentary rocks. But New York City harbors a treasure trove of rocks in the building facades, lobbies, rest rooms, storefronts, sidewalks, and curb stones, among other sites. Thanks to the rich architectural history of the city and the wide use of building stones, a great variety of rock types is readily on view not only to students of all grades but also to the general public. Many people find the fossils entombed in stone the most compelling. Some of the participants on public tours continue their search later as they travel around the city and elsewhere, looking for additional fossiliferous building stones. They are delighted when a discovery is made and on occasion call me for more detailed information about their new locality. Figures 1, 2, 3, 4, and 5 are examples of fossiliferous building stones found in New York City, while Fig. 6 was taken in a Barre, Vermont granite quarry.

Fig. 1
figure 1

Barre, Vermont granite quarry (Image by Sidney Horenstein)

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Fig. 2
figure 2

Rudistid, Trieste, Italy, Cretaceous (Image by Sidney Horenstein)

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Fig. 3
figure 3

Coral—stromatoporoid reef, Devon England, Devonian (Image by Sidney Horenstein)

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Fig. 4
figure 4

Crinoids and bryozoans, Indiana Limestone, Mississippian (Image by Sidney Horenstein)

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Fig. 5
figure 5

Clams—Texas, Cretaceous (Image by Sidney Horenstein)

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Fig. 6
figure 6

Goniatite—France, Devonian (Image by Sidney Horenstein)

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My interest in the use of building stones for teaching purposes began in the mid-1960s when I found samples of building stones in the rock collection of the Geology and Geography Department of Hunter College—City University of New York. At the time, I was teaching an evening course in introductory geology that included several units in mineral and rock identification. Although a field trip was conducted to nearby parks (including Central Park), it did not expose the students to the variety of rock formations that they would have seen on a formal bus trip to localities outside the city. Such field trips were not organized then because most of the students had daytime jobs. See Kemp (1992) and Wetzel (2002) for examples of student tours and projects related to buildings tours and class projects.

To rectify this deficiency somewhat, I asked students to examine a city street near their job or home to identify the rocks in facades. Their assignment came after the units on mineral and rocks identification were completed. Here was a practical application of what they learned in class to a real-world situation. Not only did identification of rocks become important but, students also became aware of which stones held up well in building facades and which ones exhibited signs of weathering. They were asked to evaluate the conditions that caused the excessive weathering.

I was confident that each student could identify at least ten varieties of rocks (at least one had to contain fossils), and not only did that turn out to be true but some of them also added notes about the building history, and a few added the commercial names of the dimension stones. Obviously, they did some additional homework. One of the educational rewards was that some of the students not only became interested in a practical aspect of geology but also in architecture, as well as the historical aspects of the building and its site. Thus, the study of building stones can be truly multidisciplinary, including history of mining and quarrying, tools for stone work, and for example, the labor movement in the stone industry and international financing of building projects.

For advanced geology classes, assignments can include creating an illustrated guidebook with descriptions of the buildings or structures, detailed descriptions of the mineralogy and fabric of the rock, other features such as fossils and stylolites, as well as how well the stone has performed in terms of weathering and an appropriate substitute for the poorly performing stone.

The choice of a particular stone for a project is based on many factors, including the architect’s design, availability of material, appearance of the stone, where the stone is used in the project, appropriate physical properties such as compression and water absorption, suitable mineral composition for the particular climate, and very often, cost. Because they often need less stringent requirements, stones used for interior settings contain a much broader range of rock types than those used for exterior facades, monuments, and curbing. In addition, lobbies tend to be somewhat more exuberant in color than exterior facades. Choice of material takes into account amount of rainfall, climate, and occurrence of temperatures below freezing. Another important issue is the susceptibility of a stone to disruption by crystallization of salt used to melt ice during the winter. All of these factors result in the great variety of stone available for examination during building stones field trips.

After a few semesters of teaching geology in the New York City, I began to accumulate a list of “interesting” stones in the buildings around Manhattan. Later, I led field trips for an amateur fossil club, the New York Paleontological Society, stressing the paleontological aspects of the building stones and for the general public through the auspices of the American Museum of Natural History. The free public tours organized by the fossil club were an attempt to make the group known to the public and bring in new members, while the museum field trips were part of the educational outreach of the organization.

These trips caught the attention of the press and a number of articles were written about them over the years (see, for example, Steinmann 1978; Stoler 1980; Panek 1991; McFall and Wollin 1982; Mindlin 2006). Even my children were asked to write an article (Horenstein and Horenstein 1981).