I am constantly fascinated with the way we humans utilize the natural resources around us. One of the more interesting ways is the use of stone to decorate the exteriors of our homes and businesses.

Do we decorate these structures in elaborate ways as a tribute to nature's creations? Is it some primal need to encapsulate our living quarters with parts of Mother Earth? Is it a form of self expression or ego that we want our buildings to look "different," or is it the opposite -- we want to look like the neighbor's house?

Or, perhaps we simply learned after trial and error that these materials tested the weathering of time and give us the best shelter from the elements. Maybe it's a bit of all of the above, but nonetheless we've come a long way from the days of living in caves.

While homes today are mostly plywood with a veneer of bricks (or, ugh, aluminum siding), you can still find commercial buildings which utilize building stone for their facades. For example, some of the stone that lies on the Empire State Plaza is Anorthosite, the same igneous rock that makes up much of the highlands on the Moon!

Many of the 19th century buildings in Troy have beautiful facades of carved stone that are a bit more down to Earth.

Beside the use of bricks, wood, iron and steel, there are a number of rock types that were popular for building purposes especially during the 19th century: Granite, marble, slate, limestone, sandstone, brownstone, and bluestone.

Limestones are sedimentary rocks deposited in ancient oceans and often contains numerous fossils. New York was covered with several oceans over the last millions of years.

There are extensive limestone deposits in New York State that are as old as the Cambrian period, some 500 million years ago (mya). Besides building stone, limestone is used for making concrete and natural cement (was used to build the Erie Canal).

Marble is a metamorphosed limestone or dolostone and is found in the St. Lawrence, Westchester and Dutchess Counties. Nearby Vermont marble was popular in Troy, especially for gravestones, but that is another story.

Granite is actually a variety of light colored igneous and metamorphic rocks and in New York mainly come from the Adirondack region or in Westchester County. New York's granites are really mainly gneisses, a layered metamorphic rock with the composition of granite.

You see granite in 19th century paving stones as well as building facades because of its durability.

Sandstone was formed from the minerals and fragments deposited in ancient seas and was used for building and curbing. In New York, the Triassic/Jurassic period (206 mya) rift basins in the Ramapo area south of us have extensive sandstone deposits. Yes, that is the period when dinosaurs were roaming the Earth. The only dinosaur found in New York State came from this area (Nyack, Rockland County) and was in the form of footprints of the 3 meter long carnivorous Coelophysis.

A commercial type of sandstone known as bluestone only comes from New York and Pennsylvania and is middle to late devonian age (380 million years old).

Brownstone is a dark brown or reddish coarse-grained arkosic (rich in feldspar) sandstone and was popular during the middle and late 19th century for facades, similar to our craze for aluminum siding in the 60's.

There are several varieties of sandstone that were used in building. Medina Sandstone of the Silurian period (400+ million years ago). Potsdam sandstone for veneers is Late Cambrian age (490 mya). Rensselaer Graywacke of Cambrian age (500 mya) was once used for building also.

Slate is a metamorphosed shale and comes in a variety of colors such as red, green, gray, green, purple, black and a variegated purple and green. Slate was mostly used as a roofing material. The New York/Vermont slate belt is the only one is America that produces red, green, purple and variegated colored slates.

Slate is mostly mined in Washington County in New York. Red Slate is on the New York side and is one of the most popular colors for buildings.

Not all of the buildings in Troy used material from local New York quarries. In fact, some were exported from great distances as the builders wanted a particular color or grain or look on their building. Some varieties of these stones held up better to the elements.

Take a walk around downtown and see how many buildings you can find that have facades composed of the rock types mentioned above. Here are a couple to get you started.

The Hart Mansion (Rensselaer County Historical Society) at 51 Second Street has a facade of Westchester marble, commonly called Sing Sing Marble, because inmates were later used to quarry it.

The Veil House on First and Congress has window lintels made from marble from the Stockbridge-Lee area of Massachusetts.

Check out the Brownstone front on the old Young Women's Association building (now Allegro's) at 33-35 Second Street.

One of the more interesting facades is the one on the building of the Northeastern Science Foundation at 15 Third Street. When Dr. Gerald Friedman purchased the building in the 80's, he had Salem Limestone from the Bloomington/Bedford area in Indiana imported. It is a very fine grained limestone with uniform particle size and many fossil fragments.

You see limestone is known as a 'carbonate' in geology circles. Dr. Friedman, a geologist, specializes in carbonates and evaporites (halite or salt, for example), and even published a scientific journal called the Carbonates and Evaporites Journal. Dr. Friedman wanted this Mississippian aged rock (350mya) to symbolically adorn the building.

Come to think of it, maybe we have not evolved from the caves as much as we think. Afterall, as in prehistoric times, we continue to live and work in structures surrounded by natural rock.