Note 3077 — BOOK XXXVII. THE NATURAL HISTORY OF PRECIOUS STONES.
John Bostock translation
There is some truth in this, as some few kinds both of the Garnet and Ruby are infusible. Of the ruby, the red varieties change to brown, black, and opaque even, as the temperature increases, and on cooling become first green, and then nearly colourless, but at last resume their red colour.