Reading Mosiah 27, to my surprise I saw a chiastic structure here as well. I have never seen it pointed out before, but it certainly includes a lot of the elements and criteria for a chiasmus that I know of.
A: 11
And as I said unto you, as they were going about rebelling against God, behold,
the angel of the Lord appeared unto them; and he descended as it were in a
cloud; and he spake as it were with a voice of thunder, which caused
the earth to shake upon which they stood
B: 12
And so great was their astonishment, that
C: they fell to the earth,
D: and understood not the words
which he spake unto them.
E: 13 Nevertheless he cried again,
saying: Alma, arise and stand forth, for why persecutest thou the
church of God? For the Lord hath said: This is my church, and I will
establish it; and nothing shall overthrow it, save it is the transgression of
my people.
F: 14 And again, the angel said:
Behold, the Lord hath heard the prayers of his people, and also the prayers of
his servant, Alma, who is thy father; for he has prayed with much
faith concerning thee that thou mightest be brought to the knowledge of the
truth;
G: therefore, for this purpose have I
come to convince thee of the power and authority of God, that the
prayers of his servants might be answered according to their faith.
G': 15 And now behold, can ye
dispute the power of God? For behold, doth not my voice shake the
earth? And can ye not also behold me before you? And I am sent from God.
F': 16 Now I say unto thee: Go, and
remember the captivity of thy fathers in the land of Helam,
and in the land of Nephi; and remember how great things he has done for them;
for they were in bondage, and he has delivered them.
E': And now I say unto thee, Alma,
go thy way, and seek to destroy the church no more, that their prayers may
be answered, and this even if thou wilt of thyself be cast off.
D’: 17 And now it came to pass that these
were the last words which the angel spake unto Alma, and he departed.
C': 18 And now Alma and those that were
with him fell again to the earth,
B': for great was their
astonishment; for with their own eyes they had beheld an angel of the Lord;
A': and his voice was as thunder, which
shook the earth; and they knew that there was nothing save the power of God
that could shake the earth and cause it to tremble as though it would part
asunder.
Could it be that Mormon knew about the chiastic structure of Alma's words to Helaman on the plates of Nephi and decided to create a chiasmus himself when abridging the record of Alma's conversion in the Book of Mosiah?