_Sapphire._--A variety of native corundum or aluminium sesquioxide. As the name of a gem the term is restricted to the transparent varieties of blue, pink, yellow, and other colors. The best specimens of the blue variety are nearly as valuable as the diamond. The sapphire is next to the diamond in hardness.
_Sard._--A variety of carnelian, of a reddish-yellow or brownish color.
_Sardonyx._--A variety of onyx consisting of sard and white chalcedony in alternate layers. (See onyx.)
_Spinel._--A mineral occurring in octahedrons of great hardness and various colors, as red, green, blue, brown, and black, the red variety being the gem spinel ruby. It consists essentially of aluminum magnesium, but commonly contains iron and sometimes also chromium. The fine specimens of spinel ruby are worth rather more than half as much as the diamond.
_Topaz._--A mineral occurring in rhombic prisms, generally yellowish and pellucid, also colorless, and of greenish, bluish, or brownish shades. It sometimes occurs massive and opaque.
_Tourmaline._--A mineral occurring in three-sided prisms. Black tourmaline is the most common variety, but there are also other varieties, as the blue (indicolite), red (rubellite); also green, brown, and white. The red and green varieties, when transparent, are valued as jewels. The finest ones come from Maine, and are worth four or five times as much as garnets.
_Turquoise._--A hydrous phosphate of alumina containing a little copper. It has a blue, or bluish-green color, and usually occurs in kidney-shaped masses with a nodular surface like that of a bunch of grapes. The finest specimens are worth nearly half as much as diamonds.
_Verd antique._--A mottled-green, serpentine marble, also a green porphyry, which is called oriental verd antique.
_Zircon._--A mineral usually of a brown or gray color. It consists of silicon and zirconium, and is harder than the garnet. The transparent varieties are used as gems. The red variety is called Hyacinth; a colorless, pale yellow, or smoky-brown variety from Ceylon is called jargon.
=Gold=, a metal valued on account of its scarcity, color, luster, and power of resisting oxidation. It is found in nearly all parts of the world. South Africa and the United States are the leading producers. Australia, South America and parts of Europe possess important gold fields.