Colorado Yule Marble; building stone of the Lincoln Memorial

The Colorado Yule marble, quarried in Marble, Colo.,
is a very pure white marble, and it has been widely
acclaimed for its quality and purity. This marble has been
used for many prominent buildings; one of the most notable
is the Lincoln Memorial in Washington, D.C., built nearly
80 years ago. Although most of the marble in the memorial
appears to be in very good condition, some of the stones
have developed pronounced surficial roughness and show a
significant loss of carved details and rounded edges
compared with adjacent stones. Because adjacent blocks of
marble receive nearly identical exposure to weathering
agents that cause deterioration of the marble, it seems very
likely that this pronounced difference in durability of
adjacent stones arises from some inherent characteristic of
the marble.
The Colorado Yule marble is a nearly pure calcite marble
with minor inclusions of mica, quartz, and feldspar.
Compositions of the calcite and the inclusion phases in the
marble are typical for those phases. The calcite grains that
compose the marble are irregularly shaped and range from
100 to 600 micrometers in diameter. The texture of the marble
is even, with a slight preferred directional elongation
that is visible when the marble is cut in certain directions.
Physical tests of the marble show that its strength is comparable
to that of other marbles typically used in buildings.
Variations in the durability of the marble, like those
seen at the Lincoln Memorial, are not related to variations in
calcite composition or to the presence of inclusions in the
marble. Most likely, the variations arise from differences in
the calcite grain boundaries and the degree to which the
grains interlock with one another. Weak grain boundaries
that permit water or solutions to penetrate into the marble
and dissolve the calcite grains at their edges cause the marble
to disaggregate or ?sugar.? Subtle differences in texture
that occur in the marble from various parts of the quarry
probably cause some stones to be more susceptible to this
form of deterioration. These differences may not be readily
visible when the stone is freshly quarried.