Chanthaburi, town (1990 pop. 40,049), capital of Chanthaburi prov., SE Thailand, near the Gulf of Thailand. It is an agricultural trade center in an area growing rice, pepper, and coffee. Prec...

Ratnapura [Sinhalese,=city of gems], town (1995 est. pop. 46,000), SW Sri Lanka. Located in a rubber- and rice-producing area, Ratnapura is Sri Lanka's major precious-stone center, with ruby a...

Corundum, mineral, aluminum oxide, Al2O3. The clear varieties are used as gems and the opaque as abrasive materials. Corundum occurs in crystals of the hexagonal system and in masses. It is tr...

Amethyst [Gr.,=non-drunkenness], variety of quartz, violet to purple in color, used as a gem. It is the most highly valued of the semiprecious quartzes. It is associated with a number of super...

Lapis lazuli, gem, deep blue, violet, or greenish blue in color and usually flecked with yellow iron pyrites. It is composed of lazurite, a complex sodium aluminum silicate, mixed with other m...

Tanzanite, beautiful gemstone discovered in 1967 in the Umba Valley near the Usambara Mts. in Tanzania, a precious variety of the mineral zoisite, a calcium aluminum silicate. Zoisite is a com...

Month, in chronology, the conventional period of a lunation, i.e., passage of the moon through all its phases. It is usually computed at approximately 29 or 30 days. For the computation of the...

Tourmaline, complex borosilicate mineral with varying amounts of aluminum, iron, magnesium, sodium, lithium, potassium, and sometimes other elements, used as a gem. It occurs in prismatic crys...

Titanium [from Titan], metallic chemical element; symbol Ti; at. no. 22; at. wt. 47.88; m.p. 1,675°C; b.p. 3,260°C; sp. gr. 4.54 at 20°C; valence +2, +3, or +4. Titanium is a lustrous silver-w...

Watch, small, portable timepiece usually designed to be worn on the person. Other kinds of timepieces are generally referred to as clocks. At one time it was generally believed that the first ...