The Texas State Gemstone: Blue Topaz. Topaz is the Texas state gemstone as well as the birthstone for the month of November. It occurs naturally in many colors including blue, orange, brown, green, pink, beige and red. Colorless topaz, a common variation, can be treated by irradiation to produce a wide range of shades of blue. Thus treated, blue topaz is one of the most popular and widely used of all gemstones.