The best of these gems of Mercury are a brilliant green, smooth and transparent and without dots or spots. Emeralds attract wealth and give the wearer intelligence and good health. They drive out evil spirits and cure defects of the eyes, regulate blood pressure and nerve ailments. These gemstones improve faculties related to the brain, such as memory, communication, intuition, the intellect, and the ability to learn. However newly married couples should not wear them as they impair desire. Emerald was once worn to guard against plague and the bites of venomous reptiles. Tradition had it that the emerald breaks when he or she who wears it is unchaste; even today the belief is that the stone will darken if the spouse if faithless. Apparently a snake will be blinded if it gazes upon emerald. The emerald is best worn when Mercury is in Virgo, or on a Wednesday, on the ring finger of the right hand and weigh at least 3 carats. EMERALDCHEMICAL COMPOSITIONBe3 Al2Si6O18COLOURGreenREFRACTIVE INDEX1.57-1.58RELATIVE DENSITY2.67-2.78HARDNESS7-8CRYSTAL GROUPPrismaticCLEAVAGEBasal, PoorFRACTUREConchoidal to UnevenTENACITYBrittleLUSTREVitreousTRANSPARENCYTransparent to TranslucentDISPERSIONLow, .014BIREFRINGENCELow , .005-.009PLEOCHROISMWeakLOCATION: Afghanistan, Australia, Austria, Brazil, Colombia, India, Madagascar, Mozambique, Pakistan, Russia, South Africa, United States.