This is an original Sunstone from the Nauvoo Temple. Here is a brief explanation of the temple from the Church History Museum in Salt Lake City, Utah.
The walls of the temple featured 30 pilasters, each with a moonstone at the base and a sunstone at the top. A sunstone served as the capital, or head, of each pilaster. A star stone was placed above each sunstone. The order of the stones recalled the woman described in Revelation 12, “clothed with the sun, and the moon under her feet, and upon her head a crown of twelve stars” (Rev. 12:1). When the original temple was under construction, the New York Spectator published the following review of the temple sunstones in an article about Nauvoo: “On the top, not far from fifty feet high, is an ideal representation of the rising sun, which is a monstrous prominent stone face, the features of which are colossal and singularly expressive. . . . These all stand out on the stone boldly. Their finish is admirable and as complete as any of the best specimens of chiseling on the Girard College at Philadelphia.”Continuing:
The first sunstone was installed on September 23, 1844.7 The original sunstones were actually two pieces of stone. The lower, face portion was carved from one piece of limestone, and the trumpets from another. The sunstones were six feet high and six feet six inches wide at the top.This is one of the amazing artifacts in the National Museum of American History in Washington, D.C.