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 Interest and Enjoyment by Martin Cooney

PART 6) VARIATIONS IN THE YULE MARBLE

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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VARIATIONS IN THE YULE MARBLE

By Elaine S. McGee 

The calcite grains in a marble interlock to form a network of crystals

Grain size and shape have been identified as key factors in stone durability. The calcite grains in a marble interlock to form a network of crystals; therefore, the grain boundaries in marble are likely to be weak points where dissolution can occur.

Dale (1912) suggested that although fine-textured marbles present more surface area for rain water to react with the calcite, a coarse-grained, loose-textured marble may allow water to move more rapidly along the grain boundaries and speed deterioration of the marble.

Water penetration key to rate of deterioration

The width of the grain boundaries also influences the rate of deterioration. If the openings are very small, water cannot easily penetrate, but slightly wider openings allow water to penetrate and dissolve the marble along the grain edges. However, once the grain width boundary expands, dissolution of the boundaries may be less effective in widening the openings, and the weathering rate may decrease.

So as time passes, the effect of water penetration in marble along grain boundaries will change. Bain also observed that the width of grain openings is not the only factor that influences marble durability. Thin sections of marble examined with the optical microscope show that smooth-grained marbles have distinct grain boundaries compared to irregularly grained marbles.

Cut of the block can influence the resistance to weathering

Bain stated that deeply crenulated grain boundaries may account for the weathering resistance of some marbles because the spaces between grains must be widened enough to free adjoining crystals. By measuring the grains per square centimeter and the length of con tact of the grains (centimeter per square centimeter), Bain devised a coefficient of irregularity for marbles.  He defined the coefficient as the length of contact between grains on a surface divided by the square root of the number of grains exposed on that surface.  He used the coefficient to indicate which marbles might be more resistant to weathering.

According to Bain, the coefficient of irregularity for marbles is typically 1.8, but it may range from highly irregular (deeply crenulated) to nearly smooth boundaries.

Another factor that can influence the resistance of the calcite grains to dissolution is orientation of the crystals. Marble blocks cut so the exposed faces parallel the basal face of the calcite crystals may be more weather resistant because the basal faces of the calcite crystals are less soluble than the prism edges.

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Grain samples appear tightly locked and fairly angular

Most features of the texture and crystal grains of the Yule marble seem to indicate that it should be resistant to weathering.  The grains in samples examined in thin sections appear to be tightly interlocked, they are fairly angular, and there is a mixture of grain sizes in many areas of the samples.

Bain gave the coefficient of irregularity for four Yule marble samples as 2.06, 2.00, 1.95, and 1.91. All the values are above the typical value of 1.8, indicating that the marble samples would be likely to be resistant to weathering.

Preferential orientation may account for weather resistance of block

In some samples of the Yule marble, the calcite grains appear to be slightly elongated. One of the special characteristics of the Yule marble is the preferred orientation of the marble grains observed if the stone is cut in certain directions.  This preferential orientation may also account for some of the weather resistance of some of the blocks of marble in the Lincoln Memorial. Unfortunately, it is difficult to determine what the width and amount of crenulation of the calcite grain edges were on the stones that have weathered poorly at the Lincoln Memorial.

Yule quarry marble characteristics vary with the origin of the block within the quarry

Bain and Vanderwilt both pointed out that marble from the Yule quarry varies depending on the part of the quarry that it is from.  Bain identified three areas—the east side, the bench, and the west side— that show distinct differences in integrity of the stone.

Vanderwilt described the east-side marble as a relatively coarser grained, soft stone, with a high ratio of absorption (has a tendency to absorb moisture).  He stated that the marble from the east side is not suitable for exterior work because it crumbles readily, and the polished surfaces lose their smoothness after a few years of exposure.

East section marble softer than other areas of the quarry

After the Yule quarry was reopened in 1990, the company found that marble from the east section of the quarry was softer than marble from other areas of the quarry.  In contrast, the marble from other portions of the quarry appears sound.

Bain described the west-side marble as very well preserved; the bench marble is intermediate in quality. Because of the nature of this marble deposit, it seems entirely possible that there might be variations in the characteristics of this marble, depending on its location in the quarry.

Yule marble was formed from Contact Metamorphism

The deposit was formed from contact metamorphism, meaning that a local rather than a regional heat source caused the original limestone to recrystallize to form marble. Thus, the amount and degree of metamorphism within the marble body might have varied across the deposit depending on its proximity to the granite intrusion (the heat source) that caused the stone to recrystallize.

Grain size, degree of recrystallization of the calcite, and types of inclusions other than the calcite that are present in the marble are features that vary with the amount of heat and pressure that the marble experienced during metamorphism.

Variation in deterioration may be due to stones being taken from different parts of the quarry

Vanderwilt and Bain both reported that there are grain size variations in the marble body and that the marble that is in direct contact with the granite is very coarse grained.  Both reports also describe inclusions, such as bodies of “lime,” some garnet, and dolomite, that are present in some areas of the marble body but absent from others.

It seems quite likely that some of the variation in deterioration of the stones at the Lincoln Memorial may be because the stones were taken from different parts of the quarry.  Merrill and Vanderwilt both reported that, at the Yule quarry, impurities and variations in quality were encountered along joints in the stone.

Butler’s correspondence from the quarry indicates that several fairly thick layers of flint and lime were removed in order to obtain pieces for the Lincoln Memorial.

Stones from several different areas of the quarry were used

To supply large blocks that met the sample standards and to replace stones that failed in cutting or were rejected at final inspection, several different areas of the quarry were used.  Unfortunately, we do not know where specific stones came from in the quarry.  However, some of the distinctive features of the marble are present only in some areas of the memorial, suggesting that certain characteristics were typical of the areas used for that particular stone size.

For example, a number of the column drums have broad flat areas that appear as chalky white inclusions.  This particular feature is not seen on any of the other areas of the building, such as walls, steps, and cheneau.

Cracks in the stones are rare

Because the stones were all inspected prior to acceptance, one would anticipate that there should be little variation in the quality and characteristics of the marble in the Lincoln Memorial.  However, the primary focus of the inspections was to find stones that fell within the established standards for veining and to reject stones with cracks or seams that might become cracks.

The stones that now show significant differences in deterioration at the Lincoln Memorial most likely would have met the inspection criteria, because most do not contain significant inclusions; cracks in these stones are rare.

Features that indicate future deterioration too subtle to detect?

The primary characteristic of the more deteriorated stones is extreme sugaring of the surface and pronounced rounding of edges and carved features.  It is possible that even though the stones were carefully inspected, features that might have indicated that some stones would tend to sugar more than others may have been overlooked because that was not of primary concern in the inspections.

Alternatively, it may have been difficult to identify these stones when the memorial was being built because the features that would indicate future extreme sugaring may have been too subtle to see before significant stone exposure occurred.

Variable stone integrity recognized at the Lincoln Memorial

If variations in the integrity of the Yule marble are a typical feature of the marble, then it is likely that they would have appeared in other buildings.  However, once the variable stone integrity was recognized at the Lincoln Memorial, and if a characteristic that caused the variable integrity was identified and could be avoided, then younger buildings should show more uniform deterioration than the Lincoln Memorial.

By examining buildings with exterior Yule marble, it may be possible to determine whether variable durability is a common feature.  It may also help to determine whether the problem was restricted to stone quarried at a specific time or from a specific part of the quarry.

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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 Interest and Enjoyment by Martin Cooney

PART 6) VARIATIONS IN THE YULE MARBLE

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Next

PART 7) CONDITION OF THE YULE MARBLE IN OTHER BUILDINGS … Click Here

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The Story of Colorado Yule Marble

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