Generally agate's hardness is a 6.5-7 on Moh's scale, with a waxy luster. Although some agates have the appearance of glass, it is much harder: glass is typically only as hard as a 5.5. Agate is quite abundant and most varieties are very inexpensive, yet some still use glass to imitate it. A simple scratch test will prove whether your gem is agate or glass. Many glass marbles are made to imitate agate, and there are also many beads on the market sold as imitation agate.
Agate typically appears in gray, blue, yellow, or brown shades, and sometimes red. Green and blue are the most rare of agate colors. Agate takes dye and color treatments well, which I will discuss along with geodes - bright and neon colors such as bright blue, bright purple or bright pink are indicative of dye.
Idar-Oberstein, or at the time Oberstein, Germany, was the biggest name in cutting and processing agates, dating back to 1497. This included cutting European imports of South American agate, and dyeing. Low-cost energy provided by the Nahe River ran the cutting and polishing machines, and labor was inexpensive. Oberstein prospered until local gemstone quarries dwindled; many laborers left for Brazil and other South American gem excavation sites, creating a new gem economy. While Oberstein has recovered in the years since WWII, it has steep competition from Thailand and India.