Ruby spinels, garnets, hyacinths, red quartz, burnt Brazilian or rose topaz, and red tourmaline are sometimes passed off for the ruby.
The true ruby will scratch all of these stones readily, the spinel is lighter in specific gravity, and has generally a slight tinge of yellow, even in the most pronounced red specimens.
The ruby will turn green under the flames of a blow-pipe, but when cooled off, resumes its original color.
The garnet and topaz are easily scratched by the ruby, the hyacinth is heavier, and quartz and tourmaline lighter than the ruby. Some so-called reconstructed rubies, recently offered for sale, are of a very fine color, and closely resemble the Oriental gems.
The hardness and specific gravity are the same, but they differ in one very important point, namely: they lack the brilliancy of the true ruby. In addition to this lack of fire, a microscopical test discloses formations which will distinguish the manufactured from the natural stone.
Sapphire.
The blue corundum, ranging in color from the lightest blue to deep blue and black, is the same stone as the ruby, the only difference being in the color.
The choicest color is the soft velvety blue, approaching the corn-flower in shade and exhibiting that color vividly by artificial as well as by natural light.
The deeper-colored stones are known as male, and the light-colored ones as female sapphires.
Although choice sapphires are rare, a much greater quantity of good and large stones are to be had than of rubies, and therefore the price of a large sapphire does not advance in the same proportion as the price of a large ruby.