The US National Park Service "officialy" verifies your claim:
"The Monument?s aluminum metal apex, representing a small pyramid,
5.6? on each base side and 8.9? high was set December 6, 1884, on top
of the 3,300-pound capstone. The apex was engraved with the names of
the engineers and notables who completed the monument, and on one side
contained the words: Laus Deo, Praise God."
"This article was taken from the Internet web-site of the National
Park Service, District of Columbia. It is the abbreviated version of a
longer, fully detailed and illustrated article by Bro. Scott on the
Masonic stones of the Washington National Monument."
Gary T. Scott, 32, K.C.C.H. is not only a Mason but is official Region
Historian, National Capital Area for the National Park Service. I
guess that makes it pretty solid.
The above information is from the website of "The Scottish Rite
Journal" - "Masonic Stones of the Washington Monument"
Here is a photo of a replica of the aluminum capstone showing how the
- From the website of the "Journal of the Minerals, Metals, and
terms - pyramidium washington monument, aluminum pyramidium washington
monument, engraving aluminum pryamidium washington monument, aluminum
capstone washington monument
If I may clarify anything, please ask.