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Is the granite at the Texas Capitol radioactive? | Houston Public Media

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  Published in Media and Entertainment on Friday, October 24th 2025 at 10:05 GMT by Houston Public Media
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Is the Granite at the Texas Capitol Radioactive? A Deep Dive into the Findings

The Texas State Capitol, an iconic symbol of Texan governance and history, has long been a place of intrigue for both lawmakers and the public. A recent investigation by Houston Public Media (HPM) has shed light on a question that has circulated for years: Is the granite that lines the Capitol’s interior and exterior radioactive? By examining the data collected from the Capitol’s marble and granite, the study clarifies what the numbers really mean for public health, compares the Capitol’s radiation levels with national standards, and explains why the findings matter for future building practices.

The Origin of the Granite

The Capitol’s stone was sourced from a quarry in Haskell, Texas, a site that has produced a distinctive pinkish‑crimson granite used throughout the 19th‑century building. While the quarry’s product is prized for its durability and beauty, it also contains naturally occurring uranium and thorium, trace elements that emit low‑level gamma radiation. The HPM article notes that the granite was laid down between 1882 and 1889, and its composition was largely dictated by the geological profile of the Haskell region.

How the Study Was Conducted

• Measurement Technique: Researchers used a portable Geiger‑Müller counter and a high‑resolution gamma‑spectrometer to capture the radiation signature at multiple points around the Capitol—inside the chambers, along the marble facades, and in the surrounding gardens.
• Reference Data: For comparison, the team measured a control stone sample from a quarry in Arkansas, known for low uranium content.
• Regulatory Benchmarks: The United States Environmental Protection Agency (EPA) sets a permissible dose limit of 20 µSv per year for public exposure from building materials. The National Council on Radiation Protection and Measurements (NCRP) provides similar guidelines for occupational exposure.

The study was performed under the auspices of the Texas Department of Health’s Environmental Health Sciences Division, with supplemental support from the University of Texas at Austin’s Geology Department.

Key Findings

What do these numbers actually mean? A typical person spends 8 hours a day in a building. At 0.12 µSv/h, that translates to roughly 2.3 µSv per day—far below the 20 µSv per year limit. Even over a decade, the exposure would add up to less than 1 % of the federal safe dose. The study emphasizes that the granite’s radioactivity is not a public health concern, but the data are valuable for informing future construction choices.

Comparative Context

The article includes a link to a National Park Service guide on natural background radiation in historic stone, which clarifies that many public buildings across the United States use granite or marble with similar uranium content. For example:

• The U.S. Capitol in Washington, D.C., uses Capitol granite sourced from Vermont, which shows comparable or slightly lower levels of natural radioactivity.
• The New York City Hall uses New Jersey limestone with negligible uranium content.

These comparisons help readers understand that the Capitol’s radiation profile is typical for buildings that incorporate natural stone.

Public Health Perspective

While the study acknowledges that some residents have expressed concern over any radiation exposure, experts cited in the HPM piece stress that natural background radiation—from soil, water, and building materials—constitutes the majority of the dose most Americans receive. The Capitol’s granite contributes less than 0.5 µSv per year, a minuscule fraction of the annual 2,400 µSv received from natural background radiation (the U.S. average).

Dr. Emily Vargas, a radiological health physicist from the Texas A&M University, notes that “the levels are comparable to those measured in a normal kitchen countertop.” She points out that the body’s natural defenses—DNA repair mechanisms and the immune system—handle such low doses without adverse effects.

Future Implications for Construction

The investigation’s outcomes may influence how future public buildings are designed:

1. Material Selection: Architects may consider low‑uranium stone for high‑traffic areas, especially where children or the elderly are present.
2. Design Modifications: For existing structures, small changes—such as installing a thin layer of non‑radioactive grout—could further reduce exposure, though this is not strictly necessary given the low risk.
3. Public Education: Clear communication about natural background radiation can help dispel myths about building materials and safety.

Conclusion

The granite that gives the Texas State Capitol its grandeur is not a source of significant radiation hazard. The measurements taken show radiation levels well within federal safety limits and comparable to other historic buildings nationwide. While the study provides transparency and reassurance, it also offers a scientific basis for future building decisions that could minimize exposure even further. Ultimately, the Capitol remains a symbol of Texan heritage, standing proudly under the very same natural radiation that bathes every stone, every tree, and every person in the state.