Salisbury describes the plates as "very heavy."
Herbert S. Salisbury, “The Prophet’s Sister Testifies She Lifted the B. of M Plates,” The Messenger (Berkeley, Calif.), Oct. 1954; Church History Library, MS 4134; cited in Larry E. Morris, A Documentary History of the Book of Mormon (New York, NY: Oxford University Press, 2019), 526.
Catherine Smith Salisbury then told me that while dusting up the room where the Prophet had his study she saw a package on the table containing the gold plates on which was engraved the story of the Book of Mormon. She said she hefted those plates and found them very heavy like gold and also rippled her fingers up the edge of the plates and felt that they were separate metal plates and heard the tinkle of sound that they made.