Some of the "porphyroids" which have grains of quartz and felspar in a finely schistose micaceous matrix are intermediate between porphyries and micaschists of this group. Still more numerous are orthoschists of hornblendic character (hornblende-schists) consisting of green hornblende with often felspar, quartz and sphene (also rutile, garnet, epidote or zoisite, biotite and iron oxides).
Independently of him Klaproth in 1793 discovered a new metal in rutile, and called it titanium; he subsequently found that it was identical with Gregor's element.
The commonest titanium mineral is rutile or titanium dioxide, T102; anatase and brookite are crystalline allotropes.
Titanium dioxide, T102, occurs in nature as the three distinct mineral species rutile, brookite and anatase.
At a red heat rutile is produced, at the boiling point of zinc brookite, and of cadmium anatase.
