Aventurine

Aventurine, also known as a love stone,  was usually discovered in large deposits&mdash;blocks up to 20 lb (9.1 kg) were not unusual.

Description
This semi-precious stone was a variety of quartz that glittered when viewed from certain angles due to mica inclusions. It could be found in shades of green from medium to light, blues from dark to pale, or a warm gold. Faceting only detracted from the flash below the surface of this translucent stone, so it was tumbled smooth, cut cabochon, or used as an inlay or in carvings. A typical stone had a base value of 50 gp.

Powers
Crushed to a powder and sprinkled, thrown or blown, adventurine could dispel on contact most illusions and transformations, such as those used for disguise.