As we have said before, some other minerals exhibit this phenomenon at times. We find it in rare specimens of quartz and in some of the mica group. In some rare fragments of quartz from Siberia the stellate appearance is seen in extraordinary perfection. The six-rayed star is not only seen by refracted light, but is even visible by transmitted light. Sometimes these stones also exhibit reflections of red and blue as the direction of the stone is changed, thus combining the girasole and asteria in the same gem. Lancon relates that M. Desmaret possessed a little plate of this variety of quartz, of so great beauty and perfection as to refuse 25,000 francs for it. There is in the Museum of the Jardin des Plantes a remarkable diamond asteria; and there are also in this collection and in the cabinet of the École des Mines some superb blue and red sapphire asterias. The pure white sapphires are not often found. When well cut they exhibit a vivid eclat, and are sometimes mistaken for diamonds; but they are easily detected by the expert, since they do not possess even three fourths of the degree of brilliancy of the diamond, nor the prismatic play of color. Some of the faint-colored stones lose their tints when subjected to a high degree of heat, and improve in brilliancy and lustre. It is said that the Orientals practise this trick extensively, and sell the altered gems for diamonds. We are not aware of the refractive index of these fire-tested stones having been measured with the view of ascertaining the degree of change; but it is certain that their lustre is increased in a marked degree. Heat, however, does not affect all colored sapphires. Some of the red are often changed to deeper hues, and others are not affected. Brogniart found that the French sapphires from Expailly were actually rendered more intense in color by the action of fire. After numerous experiments with the faint-colored sapphires from Montana, we also have come to the conclusion that the stones from this locality are not perceptibly affected by long-continued heat.