Question: Why is the reference to the “brass plates” in the Book of Mormon always stated, “plates of brass?”
Answer: According to Daniel Ludlow, “In many of the Semitic languages, it is not customary to have the adjective precede the noun. Thus the Book of Mormon mentions the ‘plates of brass’ of Laban but never refers to the ‘brass plates of Laban.’”
We read that King Benjamin taught his sons, “concerning the records which were engraven on the plates of brass, saying: My sons, I would that ye should remember that were it not for these plates, which contain these records and these commandments, we must have suffered in ignorance, even at this present time, not knowing the mysteries of God.
“For it were not possible that our father, Lehi, could have remembered all these things, to have taught them to his children, except it were for the help of these plates; for he having been taught in the language of the Egyptians therefore he could read these engravings, and teach them to his children...” (Mosiah 1:3-4)
The “plates of brass” were written in Egyptian. The plates set a pattern for the use of Egyptian script (reformed Egyptian) for scribes of the small and large plates and the writings of Mormon and Moroni.
Other Semitic phrases are also found throughout the Book of Mormon, such as “altars of stone” instead of “stone altars.”
Source: 400 Questions and Answers About the Book of Mormon by Susan Easton Black, p. 62; Book of Mormon