Recently there was an entry on Houdini's grave site in Machpelah Cemetery. I found a story in the November, 1927 issue of The Sphinx magazine that goes into some detail of the materials used to construct the Houdini monument and exedra.
The story describes how the original Houdini bust was cut from Carrara, Statuary Marble. The famous Michelangelo statue of David is carved out of white statuary marble. This type of marble is 98% calcium carbonate and often has little veining, making it ideal for sculptures and statues.
The Sphinx reporter wrote that Houdini's bust was carved by A. Merli. My research has uncovered the sculptor's full name was Amadeo Merli (shown below). Merli, along with Alex Nicolai, conducted business from a studio at 23 Macdougal Alley in New York. One of the studio's better known commissions was carving the six figures for the pediment of the New York Public Library on 5th Avenue.
The SAM emblem was a Mosaic imported from Venice, Italy, by C. Francini. Unfortunately, I couldn't find out more information on this element of the exedra.
The large monument itself is made of Barre Granite. Barre is a fine granite, composed of quartz, fedspar, and mica. This work was done by The Adler Monument and Granite Works, Inc. at 148 East 57th St. The records I found showed the firm operated until 1986.
I have never been to Machpelah Cemetery, but maybe someday I will have the experience of visiting the final resting place of the great Houdini.