The birthstone for December is a combination of five different gemstones: ZIRCON (6 letters), TOPAZ (5 letters), OPAL (4 letters), GARNET (6 letters) and RUBY (4 letters). ZIRCON is a mineral composed of zirconium silicate, and is usually found in shades of yellow, green, red, brown and blue. TOPAZ is a silicate mineral that comes in a variety of colors, including yellow, orange, pink, red, blue and brown. OPAL is a hydrated amorphous form of silica, and is known for its unique play of color. GARNET is a group of minerals that come in a variety of colors, including red, orange, yellow, green, purple and brown. Finally, RUBY is a pink to blood-red colored gemstone, and is a variety of the mineral corundum.