GCBXT3V Empire State Building (Earthcache) in New York, United States created by Chet13

GCBXT3V ▼

A cache by Chet13 Message this owner

Hidden : 9/11/2026

Difficulty:

Terrain:

Size: Size: other (other)

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Geocache Description:

Welcome to the Empire State Building

In the heart of Manhattan, the Empire State Building rises above New York City as one of the world's most recognizable skyscrapers. Beyond its architecture and history, the building also contains a piece of an ancient geological environment. Much of its exterior is constructed with Indiana limestone, a light-colored sedimentary rock quarried in southern Indiana. This limestone formed approximately 330 million years ago during the Mississippian Period, when much of the region was covered by a warm, shallow sea. Today, the limestone is exposed to rainwater, atmospheric pollution, temperature changes, and other environmental conditions that have gradually altered its surface. This EarthCache invites you to examine the Indiana limestone, learn how it formed, and observe how acidic water has affected the stone over nearly a century.

The Story of Indiana Limestone

The limestone used on the Empire State Building comes from the extensive Indiana limestone deposits of southern Indiana. These deposits formed during the Mississippian Period, approximately 330 million years ago, when a warm, shallow inland sea covered the region. The sea supported abundant marine life while calcium carbonate accumulated on the seafloor. Over time, layers of carbonate sediment were buried and compacted, eventually becoming limestone. The limestone used on the Empire State Building is part of the Salem Limestone, specifically a fine-grained oolitic limestone, a formation known for its relatively uniform texture and extensive use as a building stone. Quarries around Bedford and Bloomington became particularly important sources of this material, including Empire Quarry, where the stone for the Empire State Building was quarried. Approximately 200,000 cubic feet of Indiana limestone was used on the building's exterior. The stone was eventually transported from Indiana to New York, where it became part of the exterior of the Empire State Building during its construction in 1930 and 1931.

Indiana limestone is primarily composed of calcite, a mineral made of calcium carbonate (CaCO₃). One of its most distinctive geological characteristics is its abundance of tiny rounded grains called ooids. These grains formed in the ancient shallow sea when calcium carbonate accumulated in thin layers around small particles that were repeatedly moved by waves and currents. Fossil fragments and other carbonate material can also occur within the limestone, preserving evidence of the marine environment in which it formed. The spaces between individual grains, known as pores, are another important characteristic of the rock. Although Indiana limestone is relatively dense compared with many other sedimentary rocks, its pores allow small amounts of water to enter the stone. This becomes significant after the rock is placed in a building, because its mineral composition and pore structure influence how it responds to moisture and chemical weathering. The fine-grained, oolitic texture of the Salem Limestone therefore reflects both the conditions of the ancient sea in which it formed and the properties that later made it useful as a building stone.

Indiana limestone became a popular architectural material because it combines several properties that are useful for construction. It is durable enough to survive decades of exposure while remaining relatively easy to cut, saw, and shape into precise architectural pieces. Its light color also creates the distinctive appearance associated with the Empire State Building's exterior. The limestone does not form the structural framework of the skyscraper. Instead, it serves as part of the building's exterior cladding, while the steel skeleton carries the structural loads. The limestone was cut into thousands of individual pieces to fit its complex Art Deco design, including areas surrounding windows, entrances, corners, and other architectural details. The limestone therefore represents both an ancient geological environment and a deliberate architectural choice, connecting a 330-million-year-old seafloor to one of the most famous buildings of the twentieth century.

Formation of limestone.

Empire Quarry.

Soiling & Air Pollution

Once the Indiana limestone was placed on the Empire State Building, its surface became exposed to the heavily urban environment of Manhattan. The dark or black material visible on some portions of the limestone is generally not the limestone itself changing color, but rather soiling and deposits from the surrounding environment. Vehicle exhaust, industrial emissions, airborne dust, soot, and other particulate matter can settle onto the stone's surface. Rain and wind can transport additional dirt and grime across the facade, while carbon-rich particles can adhere particularly strongly to rough surfaces, recessed areas, and architectural details. These deposits can make otherwise light-colored Indiana limestone appear gray, brown, or nearly black. The distribution of this material is therefore influenced not only by the amount of pollution in the surrounding air, but also by the shape and orientation of the stone.

In some areas, these pollution deposits can develop into black gypsum crusts, particularly on sheltered portions of the limestone. Sulfur dioxide released by the burning of fossil fuels can dissolve in moisture on the stone's surface and react with the calcite in the limestone. This chemical reaction produces gypsum, which crystallizes on the surface and can form a thin crust. The gypsum itself is white, but as it develops, it traps soot, dust, and other dark particles from the surrounding air, causing the crust to appear gray or black. These crusts are especially common in recessed and sheltered areas because direct rainfall can wash away both pollution particles and newly formed gypsum from exposed surfaces. Over time, repeated cycles of pollution, moisture, gypsum formation, and particle accumulation can produce a noticeably darker crust on protected sections of the limestone. The presence and distribution of these crusts therefore provide visible evidence of the interaction between the building's limestone, atmospheric pollution, and moisture.

Black crusting on the limestone exterior.

Tasks for This EarthCache

To log this EarthCache, visit the site and complete the following tasks. Send me your answers via Geocaching or email.

Include “Empire State Building - GCBXT3V” on the first line of your message.
Examine an accessible section of the Indiana limestone and describe its (a) color, (b) grain size, and (c) overall texture. Does the stone appear relatively uniform, or can you distinguish individual grains? How do these features reflect the environment in which the limestone formed?
Identify black crusts on the limestone and describe their (a) color and (b) distribution. Why did these crusts accumulate? Would they have formed to the same extent without as much air pollution from human activity?
Based on your observations and the information provided, do you think Indiana limestone was a suitable choice for the the Empire State Building's exterior? Justify your conclusion with specific evidence from the site.
In your log, attach a photo of yourself or a personal item at the posted coordinates with the Empire State Building. (Note: photos predating the publication of this EarthCache are not accepted.)