The Post could have better explained cracks in the Wall

Saturday, October 16, 2010

I was disappointed by the oversimplified science conveyed to readers by last week's article about cracks in the Vietnam Veterans Memorial ["New dimension to Wall's little flaws," Metro, Oct. 8].

The article stated that "the stone is no more prone to cracking than any other type of granite."

First, the stone is gabbro, although it is often incorrectly called black granite. Granite is lighter in color and vastly different in terms of mineralogy and heat absorbance. With the exception of gabbro and granite both being coarsely crystalline, they are "apples and oranges" in terms of composition, and it is composition that largely determines the degree to which materials expand and crack upon heating.

How designer Maya Lin chose to position the wall is also significant. For aesthetic reasons, she placed the wall facing south toward the sun and within a background hillside of dramatically cooler soil. This combination will certainly stress the stone over time and may be as influential to cracking as the particular mineral composition and color of the rock itself.

Kenneth Rasmussen,

Chesapeake Beach

The writer is a geology and oceanography professor.

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