Complex sentence: Analyses of cyanite often show the presence of a small amount (usually less than I%) of ferric oxide and sometimes traces of copper, and to these constituents the blue or green color of the mineral is doubtless due.
Split into simpler sentences: Analyses of cyanite often show the presence of a small amount (usually less than 1%) of ferric oxide and sometimes traces of copper. It is to these constituents that the blue or green color of the mineral is doubtless due.