Pt.8) Conclusion: Building Stone of the Lincoln Memorial, by Elaine S. McGee

An investigation of differences in the durability of the Colorado Yule marble, a widely used building stone. By Elaine S. McGee.

U.S. GEOLOGICAL SURVEY BULLETIN 2162

Building Stone of the Lincoln Memorial

Abridged and Presented for your enjoyment by Martin Cooney

PART 8) CONCLUSION

U.S. Department of the Interior / U.S. Geological Survey

Colorado Yule Marble — Building Stone of the Lincoln Memorial. Prepared in cooperation with the National Park Service Colorado Yule Marble — Building Stone of the Lincoln Memorial By Elaine S. McGee. U.S. DEPARTMENT OF THE INTERIOR: BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY: CHARLES G. GROAT, Director UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1999. Published in the Eastern Region, Reston, Va. For sale by U.S. Geological Survey Information Services Box 25286, Federal Center Denver, CO 80225 Library of Congress Cataloging in Publication Data. Manuscript approved for publication August 13, 1998.

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CONCLUSION

Praised for its quality and appearance,

early confidence in the quality of the marble appears well founded

Ever since its discovery, the Colorado Yule marble has been praised for its quality and appearance. It was selected for the Lincoln Memorial specifically because of its aesthetic attributes and the quality that it would bring to the memorial.

Although there have been concerns about variations in the marble and about the long-term durability of the marble, overall, the early praise for the quality of the marble was well founded.

Physical tests of the Yule marble do not show any significant weakness

The marble is nearly pure calcite. The irregularly shaped calcite grains are equidimensional to slightly elongate, and while they range in size, most have diameters of between 100 and 600 micrometers.

Physical tests of the Yule marble do not show any significant weaknesses; the results for the Yule marble are similar to typical results for other marbles.

Yule marble’s inclusions largely consist of Quartz, Mica and Feldspar

As a natural material, the marble is heterogeneous ( varied, mixed, assorted, diverse ). It contains inclusions of quartz, mica, and feldspar, but the inclusions are present only in minor amounts and they are unevenly distributed.

The predominant inclusion is mica, which occurs as thin traces and does not weather significantly differently from the rest of the marble.

Cheeseman Memorial, Denver

Defects were avoided once they were recognized in the early buildings that used Yule marble

In a few older buildings where the Yule marble is used on the exterior, large inclusions of quartz or feldspar have weathered to form noticeable, slightly gray, more resistant features that stand out compared to the surrounding marble.

However, specific defects such as quartz inclusions and surficial cracks in the marble are not present in more recent buildings; apparently the defects were avoided once they were recognized in early buildings that used the Yule marble.

Many blocks of marble in the quarry dump, the finishing mill and along the Crystal River appear nearly pristine

With time and exposure, the Yule marble remains remarkably white and solid.

Buildings of Yule marble and many blocks of marble in three Colorado areas—in the quarry dump, along the Crystal River, and at the site of the abandoned finishing plant at Marble, Colo.—appear nearly pristine.

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Marble deteriorates in a heterogeneous manner

However, when closely examined, one characteristic feature of this marble is the heterogeneous ( varied, mixed, assorted, diverse ) manner in which some of it has deteriorated.

In buildings in Washington, D.C., and in Denver, some surfaces of the marble retain a crisp, nearly new appearance while adjacent surfaces soften and disaggregate with severe sugaring of the calcite grains.

The composition of the nearly pure calcite grains

does not significantly in the various grades of marble

The varied durability of the marble does not appear to be related to the composition of the calcite or the inclusions.  The composition of the nearly pure calcite grains does not vary significantly in various grades and samples of the marble.

The badly deteriorated stones do not contain more distinct inclusions than their more resistant neighbors, and because the contrasts in durability occur in adjacent stones, the differences are not due to exposure of the stones to specific, local weathering.

Yule marble was formed by Contact Metamorphism

Variation in texture and grain size is a characteristic of the Yule marble deposit.

The deposit was formed by contact metamorphism, and so some portions of the marble body were closer to the intruding heat source that caused the original limestone body to recrystallize.

Thus, some portions of the marble could have been more extensively recrystallized than other portions, and the heterogeneous durability of the marble may reflect subtle differences in the resulting texture of the marble.

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Colorado Yule Marble Quarry Location

 

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Water penetrates along the grain boundaries in the marble

The pronounced surficial sugaring that distinguishes the less resistant blocks suggests that the problem may arise because of some characteristic weakness along the grain boundaries in the marble.

Weaknesses along grain boundaries would be likely if the original grain boundary widths were wide enough for water to penetrate easily or if the original calcite grains were rounded.

Metamorphism means to change form leads to changes in the mineralogy, texture, and sometimes the chemical composition of rocks.

Water is less able to penetrate blocks with grain aligned with the face

Alternatively, in resistant blocks, calcite grains may be aligned with the face of the block, so that water is less able to penetrate along weak grain boundaries.

If samples of resistant and disaggregating stones at the Lincoln Memorial were collected so that the texture and grain boundary characteristics could be examined, it might be possible to clarify the role of grain boundary characteristics in relation to the variations in durability that we see at the memorial.

Stones with pronounced weathering do not impair the structural integrity of the building

Although the stones with pronounced weathering are very distinctive on close examination, they constitute a relatively minor proportion of stones in an entire building.

Thus, although they do not present the ideal appearance, the badly deteriorated surfaces do not impair the overall structural integrity of the building.  However, the rate of deterioration may be a concern in the long term.

Knowledge of marble characteristics along with an understanding of the deterioration process, will combine to develop an effective preservation approach for the Lincoln Memorial

Where the stone of poor durability is decoratively carved or where it may be further weakened because it is exposed to direct and continual impact of weathering agents, such as along a roof parapet, its future integrity may be a concern.

If steps are taken to synthesize knowledge of the marble characteristics with an understanding of deterioration processes, specifically those that have been identified at the Lincoln Memorial, the National Park Service will be well prepared to develop an effective and timely preservation approach for the Lincoln Memorial.

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An investigation of differences in the durability of the Colorado Yule marble, a widely used building stone. By Elaine S. McGee.

U.S. GEOLOGICAL SURVEY BULLETIN 2162

Building Stone of the Lincoln Memorial

Abridged and Presented for your enjoyment by Martin Cooney

PART 8) CONCLUSION

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T H E   E N D

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The Story of Colorado Yule Marble

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