Miyashiro was known for his contributions to metamorphic and igneous petrology.
He also made contributions to the study of tectonics and meteorites.
[1] In 1973 Miyashiro challenged the common conceptions of ophiolites and proposed an island arc origin for the famous Troodos Ophiolite in Cyprus.
This was done arguing that numerous lavas and dykes in the ophiolite had calc-alkaline chemistries.
On the evening of 22 July 2008, Miyashiro visited John Boyd Thacher State Park, Albany, NY and remained there to take sunset pictures while his wife waited by the parking area.